Methods of Food Preservation

Methods of Food Preservation

Pasteurization
This method was discovered by famous biologist, Louis Pasteur. By this method milk is prevented from turning sour. In this process, milk is heated to 71 C for a few seconds and then cooled rapidly. This kills most of the bacteria. The bacteria which survive this treatment may become retarded in growth. In this way, the milk is preserved for a few days.
Refrigeration
In this methods, food is kept at very low temperature usually below freezing point. It retards the action of enzymes and the growth of bacteria. In deep freezers food can be preserved for many years. Quick freezing helps to maintain the taste and texture of meat, fruit and vegetables.
Dehydration
In this method food is dried. Such food can be kept safe for a long period at normal temperature. Bacteria do not grow without water, therefore when water content is removed from meat and vegetables, they can be preserved for long durations. Pickling of food is another common indigenous technology in which taste and texture of pickled food is maintained for long.
Canning
In this method the food is first heated at a high temperature. This kills bacteria and destroys enzymes. Then, the food is sealed in a metallic container. In this way; food becomes safe from contamination. Metallic cans are usually lacquered to prevent food from chemically reacting with metals and producing toxic substances.

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Health Problems Related to Nutrition

Health Problems Related to Nutrition

Under Nutrition
During under nutrition a person’s diet is deficient in the required calories. children are mostly affected due to availability of less than normally required diet and they suffer from a disease called marasmus. In this disease, children are reduced to a skeleton as the body becomes completely depleted. Some of the countries like Ethiopia are famine stricken. Although international community does try its best to rescue the famine inflicted areas yet it is not possible for them to meet their complete nutritional requirements on such a large scale. The world population is continuously and rapidly increasing each year. It has been estimated that by 2025, the world population will rise to ten billion, whereas water and soil resources are being continuously depleted by increasing use by the continuously growing population. The experts therefore envisage that increasing human population if not checked will soon eat up all the food resources of the world which may lead to destruction of human race.
Malnutrition
If malnutrition (a diet missing in one or more essential nutrients) continues for a prolonged period, particularly under special circumstances, such as during pregnancy or immediately after childbirth, it is found to be very harmful.
If malnutrition occurs during lactation period, it causes irrepairable damage to the infant. During the last quarter of pregnancy when foetus is rapidly developing its cerebral tissues, the protein deficient diet of the mother results in mental retardness and nervous abnormalities in foetus, which may prove fatal or lead to permanent disorders. These abnormalities may also occur in infants if the lactating mother is taking a protein deficient diet during the first year of breast-feeding.
If a human diet lacks essential elements or nutrients, the body will fail to prepare vital compounds, and thus the person will suffer from various diseases. Deficiency of a few amino acids, vitamins, fatty acids (about thirty compounds) and 21 mineral elements, called as essential nutrients in diet are responsible for various diseases.
In the poor countries like ours packaged or junk food(sugar coated cumin seeds, betal nuts, chewing gums and drinks) are not prepared under proper care. The food colours scents and flavours are added to make them commercially attractive. But these are substandard and harmful for human health. The use of food additives may be the cause of dangerous diseases like cancer and ulcer etc. These items should, therefore, be avoided.
Over Nutrition
It is the problem of the developed countries where people eat too much. Obesity is the most common disorder due to over nutrition. Obesity is the cause of a large number of diseases too.

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Balanced Diet

Balanced Diet

A diet containing essential dietary components in the correct proportion, which helps to maintain health and fulfills the body requirements of organisms, is known as balanced diet. The degree to which any particular meal is adequate in providing energy from food depends on the nature of the job of a person.
A common man’s diet is said to be suitable if it provides 50% calories from carbohydrates, 40% from fats, and 10% from proteins. Carbohydrates are abundantly used foods because they are readily available and cheaper as compared to fats and proteins. We can live without carbohydrates it our diet has all the components of food and is capable to provide total calories required by the body. Fats are taken in our diet to obtain energy. Our daily food requirement varies with sex, age and occupation e.g. children need more food because they are growing. Youth need more food than elderly people due to physical exertion. Men need more food than women. Pregnant women, lactating mother’s convalescents need more food as compared to others.

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Teeth

Teeth

Teeth
God has blessed animals and human beings with teeth. They help in breaking and chewing of the food. They are present in oral cavity.Teeth are attached to the upper and lower jaws.
Kinds of Teeth
Humans have two sets of teeth during their lives.
Milk Teeth
The first set of teeth begins to come through the gums when the baby is about six months old. these are called the milk teeth and all twenty teeth are formed over a period of two years.
Permanent Teeth
The milk teeth begin to drop out at the age of six years and are gradually replaced by the second set of teeth called the permanent teeth. In man the milk teeth do not fall off simultaneously, they fall off one by one and similarly permanent grow one by one as well. Healthy teeth are strong and give a beautiful and lustrous look. You must brush your teeth at least twice a day.
Structure of a Tooth
A tooth has two permanent parts, the Crown and the Root. The crown is that part of tooth which projects out of the gum and jaws. The root the the tooth is embedded into the gums and is therefore, hidden.
Enamel
This is the outer most part of tooth which is very hard and lustrous. It is deposited on the outside of the crown of the tooth by cells in the gum. The enamel is a non-living substance. It is made up of calcium salts. It imparts beauty to the tooth and protects the tooth. If the enamel gets removed then the teeth start decaying.
Dentine
It is the part of teeth present under the enamel which is hard. But it wears off if the enamel gets removed. Running through the dentine are strands of cytoplasm arising from the cells in the pulp. These cells keep on adding more dentine to the inside of the tooth.
Pulp
The innermost part of the tooth is hollow and is made up of soft connective tissue which is called the pulp. The strands of cytoplasm in the dentine derive their food and oxygen from the pulp which enables the tooth to live and grow. The pulp contains sensory nerves and blood capillaries. These nerve endings are sensitive to heat and cold and can produce the sense of pain e.g. toothache.
Cement
Cement is a thin layer of very hard material which covers the dentine at the root of the tooth. the fibers holding the tooth in the jaw are embedded in the cement at one end and in the jaw at the other. In this way teeth remain firmly embedded in the jaws.
Protection and Cleanliness of Teeth
Teeth are a gift of nature. For a good health, presence of clean, good healthy teeth is necessary if we wish our teeth to remain healthy; we should wash and clean them after every meal. Our tongue helps in cleansing the upper portion of teeth to some extent. If food particles are firmly trapped up between the teeth, or between gums and teeth, then it becomes difficult to remove them with the tongue. The main cause of tooth decay is a sugar coating left by sugary food on the teeth, which is converted into acid by bacteria. The acid damages the enamel and allows the bacteria to infect the soft dentine and reach the pulp cavity. The dentine begins to decay and causes toothache. Sugary foods such as sweets, toffees and chocolates, the bacteria which cause decay, form a thin layer of scum over the surface of the teeth. This layer becomes very hard with the passage of time and becomes difficult to remove. This scum is called plaque.
The teeth should be cleansed properly and regularly with a miswaak or a tooth brush. So that there is no formation of plaque. We should eat less sugar or sweet and sticky foods and also cleanse the teeth afterwards. Balanced diet should be taken, especially by young people who have growing teeth.

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Digestion of Food

Digestion of Food

Digestion of Food
First of all food comes in the oral cavity where the teeth crush and break the food and convert it into small particles. The tongue rolls the morsel of food and pushes it under teeth again and again so that the food is evenly divided into fine particles and the saliva secreted from the salivary glands gets mixed with the food. The saliva lubricates the food and makes the particles adhere to one another, forming a ball of food called bolus. Now the chemical digestion of food begins. Saliva contains an enzyme to digest starch in the food. The combined action of teeth, tongue and saliva pushes the bolus through the throat into the oesophagus, and then it reaches the stomach.
Definition of Digestion
Digestion is the process in which the insoluble and non-diffusible components of food are broken down and by the action of enzymes are converted into soluble and diffusible substance to be absorbed into the blood stream.
Types of Digestion
1. Mechanical digestion
2. Chemical Digestion
1. Mechanical Digestion
In mechanical digestion, the food consisting of large sized particle is broken into fine pieces by cutting, grinding, chewing and churning up, so that enzymes can act upon it efficiently and effectively. Mechanical digestion of food takes place in the mouth and stomach.
2. Chemical Digestion
In chemical digestion, the digestive enzymes mix with the food and act upon it to break it down further into simple and diffusible chemical forms. The enzymes act on carbohydrates, proteins and fats separately. Chemical digestion takes place in all the major parts of the digestive system. The digestive glands such as liver and pancreas also play very important role in this digestion.
Digestive System
All living things require food to live and carry on their life functions. Animals are unable to synthesize their food.
Digestion is the process in which the non-diffusible molecules of food are changed to diffusible ones by the action of enzymes. All the organs which take part in this process make a system which is called the digestive system.
Human Digestive System
The process of digestion takes place in the alimentary canal. It starts from the mouth and ends at the anus. The tube assumes different shapes according to their role in the process of digestion. It consists of the mouth, oesophagus, stomach, small intestine, and large intestine. Besides these organs liver and pancreas, also play important roles in digestion.
Peristalsis
The muscles of alimentary canal produce rhythmic waves of contraction which is called peristalsis. Due to this process, food is carried through various parts of the alimentary canal.
Ingestion
The food of animals and human is in the solid form and may be bulky. Taking in of the food in the oral cavity and swallowing is called ingestion.
Digestion of Food in the Mouth
During mastication, the food is mixed thorougly with the saliva while the food is in the oral cavity (buccal cavity). The saliva is secreted by three pairs of salivary glands located in the buccal cavity. The saliva is continuously secreted by the salivary glands in response to the presence of food in the buccal cavity.
Saliva is alkaline and contains an enzyme ptyalin. This enzyme converts starch into sugar (maltose). The morsel of food after being chewed and thoroughly mixed with the saliva is called a bolus. It is rolled down by the swallowing action into the oesophagus which conveys it to the stomach by the wave of peristalsis. The end of stomach lined with oesophagus is called cardiac end.
Digestion of Food in the Stomach
Stomach is a thick sac like structure, in which food is stored for some time. Its wall is strong and muscular. Its inner surface has numerous glands called gastric glands. These glands secrete a juice called gastric juice. Human stomach secretes about one to two liters of this juice daily; Gastric juice contains Hydrochloric acid and two enzymes, renin and pepsin. Hydrochlroic acid changes the medium of food to acidic. This medium kills the bacteria that may be found in the food. the pepsin acts on proteins and breaks them down into peptones. Renin helps to curdle milk in infants. There is no chemical action on carbohydrates and fats present in food. the regular movements of the stomach churn up the food. the food is changed into a thick fluid called chyme. When digestion in the stomach is complete, the distal end of the stomach called the pyloric end relaxes, and allows a small amount of chyme to pass into the first part of the small intestine. Food stays in stomach for about 2-3 or 3-4 hours.
Digestion of Food in the Small Intestine
Food from stomach enters the duodenum which is the first part of the small intestine. An alkaline pancreatic juice from the pancreas and bile juice from the liver and poured into the duodenum by a common duct. Both the juices contain bicarbonates which neutralize the acidic chyme and make. It rather alkaline besides these juices other intestinal juices from the walls of the small intestine are also poured. These entire juices act on food and help in digestion of food.
Liver
It is largest gland, in the body. Its colour is reddish brown. It lies just below the diaphragm on the right side of the body under the ribs. It has five lobes, three on the right side and two on the left. The cells of the liver secrete a greenish yellow alkaline fluid which is called the bile juice. It contains bile salts and bile pigments which give greenish yellow colour to the juice. Bile contains no digestive enzymes, but it does contain bile salts which break down the large molecules of fats to small fat droplets. This process is called emulsification. This process helps in the digestion of fats. Bile juice also contains bile pigments that are by products of red blood cells, these pigments are eliminated from the body along with the faeces, and the colour of faeces is due to these pigments. Besides this, bile juice also kill the germs in the food.
Functions of Liver
1. Liver stores glycogen and regulates the level of glucose in the blood.
2. It breaks down excess amino acids. this process is called deamination.
3. It is involved in detoxification.
4. It produces and secretes bile juice which is stored in the gall bladder.
5. It metabolizes carbohydrates, fats, proteins and other compounds.
6. As a result of chemical changes a lot of heat is produced, therefore liver helps to keep the body warm.
7. It makes fibrinogen and other blood proteins.
8. It decomposes the damaged red blood cells.
Pancreas
It is a leaf like organ. It lies below the stomach and between the two arms of duodenum. The pancreas produces a juice which is called the pancreatic juice. This juice flows down the pancreatic duct into the duodenum. It contains three enzymes.
1. Pancreatic amylase which acts on undigested starches of the food and converts them into maltose.
2. Enzyme trypsin which breaks down proteins into peptides.
3. Lipase which splits fats into fatty acids and glycerol.
If any of the constituents of food still remain undigested, enzymes secreted by the glands in the small intestine act upon them and complete the digestion by converting peptides to amino acids, maltose and other sugars to glucose and fats to fatty acids and glycerol.
The enzymes secreted by the intestinal walls are amino-peptidases and disaccharidase,(which form glucose from maltose, lactose and sucrose). In this way food is completely digested at intestine.

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Enzymes

Enzymes

Definition of Enzymes
Enzymes are chemical compounds. They are protein in nature. They are formed in living cells. They are not consumed in a reaction but act as a catalyst as they only speed up the chemical reactions.
Types of Enzymes
There are two types of enzymes:
1. Intracellular Enzymes
2. Extracellular Enzymes
1. Intracellular Enzymes
They work within a cell, in which they are produced.
2. Extracellular Enzymes
Some enzymes are secreted out of the cells where they work. They are called extracellular enzyme. Bacteria and fungi secrete such extra cellular enzymes into the medium in which they are growing. The higher organisms secrete extracellular enzymes into the lumen of alimentary canal to act on the food.
The enzymes acting on the starch are known as Amylases; those acting on proteins are known as Proteinases, while those acting on fats are known as Lipases.
Characteristics of Enzymes
The characteristics of enzymes are as follows:
1. All enzymes are protein in nature; they can be destroyed by heating.
2. They act best within a narrow, temperature range.
3. They work efficiently in narrow range of acidity or alkalinity.
4. A particular enzyme forms the same end-product, because it acts on a particular/specific substrate.

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Light and Dark Reactions

Light and Dark Reactions

Light Reactions
When light falls on the leaves, it is absorbed by chlorophyll. The solar energy is used to split water into oxygen and hydrogen and this is called photolysis (photo means light and lysis means to break). The oxygen is released into the atmosphere as by-product of photosynthesis. As this process takes place only in the presence of light, it is called light reaction.
During light reaction, two compounds are formed when the solar energy is converted into chemical energy these are:
1. NADPH (Nicotinamide Adenine Dinucleotide Phosphate)
2. ATP (Adenosine Triphosphate)
NADP, already exists in the cells of the leaf. The hydrogen released on the splitting of water molecule is accepted by this compound and it is reduced to NADPH.
ADP (Adenosine Diphosphate) is already present in the cell; it combines with the phosphate group using light energy to form a compound called ATP.
These compounds are energy rich compounds which are needed for the dark reactions of the process. Light reaction is called high dependent reaction.
(Diagram)
Dark Reactions
Using the energy of ATP and the NADPH, water combines with carbon dioxide to form carbohydrate. Thus the solar energy is now converted into chemical energy to form glucose. Other organic compounds are also synthesized from this glucose.
This stage is completed in a series of chemical reactions with the help of enzymes. Neither light energy nor chlorophyll is needed for dark reactions. Therefore dark reaction is also called light independent reaction.
Various steps of the dark reactions were studied by a scientist called Melvin Calvin so the dark reaction is also called the Calvin’s Cycle.

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Respiration

Respiration

CHAPTER – 10
Respiration
The oxidation of the absorbed food material in order to obtain energy is called respiration.

There are two types of Respiration in the organisms:
1. Aerobic Respiration
2. Anaerobic Respiration
1. Aerobic Respiration
In most of the higher and larger organism, the glucose etc is oxidized by using molecular oxygen. This type of respiration is known as Aerobic Respiration. In aerobic respiration a mole of glucose is oxidized completely into carbon dioxide and water releasing enormous amount of energy. One glucose molecule in this resnpiration produces 686,000 calories of energy. Aerobic respiration thus produces 20 times more energy than the anaerobic respiration.
In aerobic respiration food is oxidized in presence of molecular oxygen.
Stages of Aerobic Respiration
There are two stages of Aerobic Respiration:
(a) External Respiration
In this stage, the organisms take the air (containing oxygen) into their bodies. This is called external respiration. this stage includes the transport of oxygen obtained from the inhaled oxygen to each cell of the body.
(b) Internal Respiration
The second stage is called internal respiration. It consists of the oxidation of glucose, amino acid and fatty acids etc, with molecular oxygen. In this stage all these reactions are included which extract the chemical energy of glucose and other compounds and store it in the form of ATP molecule, this respiration is also called cellular respiration as it occurs within cells.
In the internal or cellular respiration glucose and other compounds are passed through such enzymatic reactions which release the chemical energy gradually in small amounts with the help of which ATP molecules are synthesized.
2. Anaerobic Respiration
Some organisms oxidize their food without using any molecular oxygen. This is known as Anaerobic Respiration. In this type of respiration considerably less amount of energy is released as compared with the other type of respiration.
In anaerobic respiration a glucose molecule is broken down into two molecules of lactic acid with a release of only 47,000 calories of energy.
Glucose ——–> 2 Lactic Acid + Energy (47,000 calories)
Importance of Anaerobic Respiration
1. When earth came into being its environment was totally devoid of oxygen. The aerobic organisms cannot lie in anaerobic environment. The early organisms started respiration in the absence of oxygen to produce energy for survival of organisms.
2. Some existing organisms like bacteria and parasites which live in oxygen environment have anaerobic respiration.
3. Many useful bacteria and yeasts are anaerobic.
4. Even in the aerobic respiration of the first phase is anaerobic. The glycolysis which is the first phase of carbohydrate metabolism involves reaction which does not require the expenditure of molecular oxygen. This proves the idea that aerobic organisms have evolved from anaerobic organisms.
5. In our skeletal muscles, although aerobic metabolism takes place but in sustained activity when the oxygen supply cannot keep pace with energy demand, anaerobic respiration supplies the energy continuously by the breakdown of glucose to lactic acid.
ATP (Adenosine Triphosphate)
It is a chemical compound. ATP is an abbreviation of adenosine triphosphate. Its name indicates that it contains adenosine and three phosphate groups. Adenosine is formed of a nitrogenous base called adenine and a sugar called ribose. In ATP three phosphate groups are attached to the adenosine in a series one after the other.
Significance of ATP
ATP is a big source of energy. The two terminal bonds between the phosphate groups contain large amount of the chemical energy. When these bonds are broken in enzymatic reaction, large amount of energy is released by which energy requiring activities are accomplished, like synthesis of various compounds of carbohydrates, fats, proteins and hormones etc or for carrying out any physical work like muscle contraction, heat production or transport of substances etc.
When the terminal bond is broken the ATP is changed into ADP and phosphate 7300 calories of energy are released.
Gaseous Exchange in Plants
Plants get their energy from respiration. Plants have no special organ or system fro exchange of gases. The gaseous exchange in plants occurs in cells, of every part of the plant i.e. roots, stems and leaves etc according to their energy demand. The conducting system (xylem and phloem) of plants transports water and nutrients but plays no role in the transport of gases. The air spaces present between the cells of parenchyma of leaves, stem and roots are involved in the gaseous exchange.
Gaseous Exchange in Leaves and Young Stems
In the leaves and young stems, gaseous exchange occurs through stomata. Some gaseous exchange also occurs through cuticle.
Gaseous Exchange in Woody Stems and Roots
In woody stem and roots, there are present dead cells beneath the epidermis which form cork tissue. Later on, this tissue becomes porous. The pores are called lenticels. These are involved in gaseous exchange.
Gaseous Exchange in Leaves
The aquatic parts obtain oxygen for their respiration by diffusion from the dissolved oxygen in water. Whereas the land plants get their oxygen from air directly through their stomata which are more abundant on the lower surface than the upper surface of leaves.
Gaseous Exchange in Roots
The roots get their oxygen for gaseous exchange through diffusion from the air existing in the space between soil particles.
Process of Respiration in Plants
The respiration in plants continues day and night. In this process, the oxygen from the airspaces in the leaves and stems is diffused into tissues and cells after getting dissolved in the film of water which is present over the cells. In the cells this oxygen oxidizes the carbohydrates and other organic compounds into carbon dioxide and water to produce energy. Some of the water (vapours) comes in the airspaces from where they diffuse out to the atmosphere through lenticels and stomata. The elimination of carbon dioxide is more evident from the parts without chlorophyll like growing seeds and buds. The water produced in this process becomes a part of the already present water in the body of plants. The various chemical reactions of respiration are controlled by the specific enzymes. This process occurs at a faster rate in the parts of the plant having rapid growth like growing seeds, buds, apical meristem of roots and shoots, because these parts require more energy to accomplish the growth process.
Relationship between Respiration and Photosynthesis
The gaseous exchange in plant is not very evident during the day time as the products of respiration i.e. carbon dioxide and water are used in the process of photosynthesis. In the bright sunshine, because of high rate of photosynthesis the carbon dioxide produced in respiration falls short and therefore, some carbon dioxide has to be taken into the plant from outside for photosynthesis.
In the day time the plants therefore, take in carbon dioxide and expel out oxygen. The process of photosynthesis occurs in chloroplasts whereas the process of respiration takes place in cytoplasm and mitochondria.
Gaseous Exchange in Animals
The gaseous exchange in different animals takes place by different methods and organs. In unicellular aquatic animals like amoeba, the dissolved oxygen in water diffuses directly through their cell surface into the interior of the animal and the carbon dioxide similarly diffuses out from their bodies into the external water. This is the simplest way of gaseous exchange and it can occur only in small animals with a diameter of less than one millimeter. These animals have greater surface area of volume ratio and have low rate of metabolism.
During evolution, as the animals became complex and complex and grew in their size, their skin or external body surface become impervious to water. Thus the gaseous exchange became impossible through diffusion. In large animals certain organs were developed for exchange of gases w.g. the moist vascular skin, gills, lungs and tracheoles. These large animals have developed blood vascular system which transports oxygen from the respiratory surface to the deep cells and tissues in all parts of the body. The blood in all animals has some respiratory pigments like haemoglobin which carry large amount of oxygen efficiently from respiratory surface to the interior cells.
Properties of a Respiratory Surface
1. Respiratory surface should have large surface area.
2. Respiratory surface should be moist.
3. Respiratory surface should be thin walled.
4. Respiratory surface should have blood supply.
Gaseous Exchange Through Skin
For the exchange of gases through the skin the skin must be moist and richly supplied with blood. The oxygen is diffused from the external water to the blood and the carbon dioxide is diffused from the blood to exterior water. In amphibia and fishes the gaseous exchange occurs through the skin besides through the gills or lungs. The frogs and tortoises breath through the skin during their hibernation period.
Gaseous Exchange by Gills
The gills are very effective for gaseous exchange in aquatic animals. Gills are of two types:
(a) External Gills
(b) Internal Gills
(a) External Gills
Some animals have external gills which project out of body of animals. These gills have very thin and highly vascularized surfaces e.g. the dermal papillae of star fish and arthropods.
(b) Internal Gills
These are present inside the body inner to skin e.g. in fishes and arthropods. Have you ever examined a fish closely? How ill you know that the fish is fresh or not? If the colour of gills is red then it is fresh but if the colour of gills is changed, it is definitely not fresh. The red colour of the fish gills shows the presence of oxygenated blood.
Gills of Fish
In fishes the gills are present in the branchial cavity present on lateral sides of the body behind the head. This branchial cavity is covered over by an operculum. There is a counter current flow of water and blood in gills which ensures maximum exchange of oxygen and carbon dioxide between the blood and the bathing water. Water enters through the mouth, flows over the gills and goes out of the body from the opercular aperture.
Human Respiratory System
In humans, there is very efficient respiratory system. It consists of certain organs which are called respiratory organs these include nose, pharynx, larynx, trachea, bronchi and bronchioles.
Nose
The air enters through the external nostrils into the nasal cavity. This is lined with mucous secreting epithelium and ciliated epithelium. The nostrils are lined with hairs. The nasal cavities, located above the oral cavity and behind the nose are covered with epithelial tissue.
The beating of cilia creates a current in the mucus that carries the trapped particles towards the back of the nasal cavity. From here the mucus drips into the throat and is swallowed. Mucus keeps the nasal cavities moist. Bones of the nose warm up the air. Mucus moistens the air. Hair filter the air and stop the dust particles bacteria and any other foreign substance from going to next part of respiratory system. In this way air is purified and is then pushed into the pharynx.
A number of cavities called sinuses open into the nasal cavity. The sinuses are lined with mucus secreting epithelium. The opening of sinuses into the nasal cavity is very narrow. If these openings are closed due to cold or inflammation, the sinuses get filled up with mucus this results in headache and changed voice.
Pharynx
The nasal cavity opens into the pharynx (throat) through two small apertures which are called internal nares or internal nostrils. The pharynx is muscular passage which extend from behind the nasal cavities to the opening of oesophagus and larynx. The air goes from the pharynx into the larynx.
Larynx
The upper most part of the wind pipe (trachea) is called the larynx. The larynx is a cartilaginous box. Two fibrous bands called vocal cords are located in this box. These vibrate to produce sound. Larynx is, also called sound box or voice box. The air enters the larynx through a small aperture called glottis which is guarded by a muscular flap called epiglotis which fits into this opening while the food is being swallowed into the oesophagus. It prevents the food from entering into the trachea and choking it. During breathing epiglottis keeps the glottis open so that air goes to trachea.
Trachea
The air tube (wind pipe) is known as trachea. It is about 12 cm long and lies in front of the oesophagus. It has incomplete C shaped cartilagenous rings which are regularly placed in its wall and all along its length. These rings prevent the collapsing of the tube nd thus keep the air passage wide open all the time. Trachea is also lined with ciliated mucous epithelium. Any foreign particles present in the inhaling air get trapped in the mucous that is moved out of the trachea by breathing of the cilia in the upward direction. In trachea air is further cleansed and filtered and then moved towards the lungs.
Bronchi
The trachea while passing the chest cavity divides into two smaller tubes which are called bronchi (single bronchus). Bronchi are similar in structure to the trachea but are smaller in diameter and they have in their walls small irregular catilageuous plates. Each bronchus enters into the lungs of its own side. The right bronchus divides into three secondary bronchi and the left bronchus divides into two secondary bronchi which serve the 3 right and 2 left lobes of the lungs respectively.
Bronchioles
the secondary bronchi further divide into very fine branches until they end in thousands of passage ways called respiratory bronchioles. The bronchioles have not cartilaginous plates in their walls. They have smooth muscle and elastic fibers.
Alveoli
The walls of the respiratory bronchioles have clusters of tiny branches(like bunches of grapes) that along with the respiratory bronchioles re the sites of gaseous exchange, these pouches or air sacs are called alveoli (singular: alveolus). The alveoli are enormous in number. Each lung has about three hundred million alveoli.
Pulmonary artery brings deoxygenated blood from the heart into the lung. Here, it divides and re-divides until it forms a network of fine capillaries over the wall of each alveolus. The walls of alveoli are very thin (1/1000 mm thick) and moist. Thus, alveoli are efficient site for gaseous exchange.
The Lungs
There is a pair of lungs present in the chest in man. Actually, the masses of alveoli constitute lungs and their lobes. The lungs re protected by the chest box from sides and by a doem shaped muscular diaphragm from below. Chest box or ribcage is made up of ribs. Between the ribs, there are present inter-costal muscles. The diaphragm is a muscular sheet which partitions the chest and abdomen.
The two lungs re covered by a double layered membrane called pleural membrane. There is a thin film of fluid in between the two layers. This watery fluid makes the movements of the lungs (expansion and contraction) easy. It also protects the lungs from external injuries.
(Diagram)
Mechanism of Breathing
Breathing occurs in two phases:
1. Inspiration
2. Expiration
1. Inspiration
1. During inspiration, the dome-shaped diaphragm contracts and becomes flat some what and thereby lowering the floor of the thoracic cavity.
2. The external inter-costal muscles contract raising the ribcage. A combined action of these two events expands the thoracic cavity, which in turn expands the lungs.
3. The air pressure within the lungs decreases.
4. Thus air from the environment outside the body is pulled into the lungs to equalize the pressure of both sides.
2. Expiration
1. The diaphragm relaxes and assumes dome like shape. During expiration, the external inter-costal muscles relax and the internal inter-costal muscles contract as a result of which ribcage drops.
2. The combined action of these two event decreases the volume of the thoracic cavity which in turn decreases volume of lungs.
3. The air pressure with in the lungs increases.
4. The air is thus forced out of the lungs.
Bad Effects of Smoking on Heath
Smoking is injurious to human health. The smoke contains many chemical and gases. Dried tobacco leaves are used in cigarettes. The tobacco on burning produces a number of dangerous and toxic compounds.
Chemicals Present in Cigarette Smoke and Their Harmful Effects
(a) Nicotine
1. Man is addicted to cigarette damages brain tissues.
2. Causes blood to clot more easily.
3. Harden walls of arteries.
(b) Tar
1. Kills cells in air passages and in lungs.
2. Increases production of mucous and phlegm in lungs.
3. Causes lung cancer.
(c) Carbon Monoxide
Prevents red blood cells from combining with and transporting oxygen around the body.
(d) Carcinogens
promote the growth of cancerous cells in the body.
(e) Irritants
1. Irritate air passages and air sacs in the lungs.
2. Kill cells at the surface of air passages.
3. Causes smoker’s cough and lung cancer.
Combustion
A chemical reaction in which a substance combines with oxygen and produce heat, light and flame is called Combustion.
Respiration
A process that liberates chemical energy from organic molecules when oxidized is called Respiration. It occurs in all living cells. In fact respiration is a series of complex oxidation and reduction reactions in which energy is released bit by bit.
Photosynthesis
The process in green plants by which green plants manufacture their own food by using carbon dioxide and water with the help of energy absorbed by chlorophyll from sunlight is called photosynthesis.
Relation of Combustion, Respiration and Photosynthesis
Combustion is the process of burning in which wood, coal, methane, gas etc are burnt in the presence of oxygen, producing carbon dioxide and water accompanied with the release of energy. It is an exothermic chemical reaction.
Cellular respiration can be compared to burning of fuel in which organic food (carbohydrates, fats and proteins) rich in carbon burn in the presence of oxygen producing carbon dioxide, water and energy.
Respiration like combustion is a catabolic exothermic chemical process. However, the difference between the combustion and respiration is that the combustion takes place in one go, releasing the entire energy as the heat, which may be utilized or is lost into the environment. the respiration completes in several small steps. Each step is under the control of a specific enzyme, releasing energy in small amounts which can be stored in the form of ATPs. Photosynthesis, another metabolic process, is just opposite to combustion. Combustion is a catabolic process; the photosynthesis is an anabolic process. In photosynthesis organic substance is synthesized from carbon dioxide and water in the presence of sunlight energy and chlorophyll. The molecular oxygen is evolved as the by-product combustion is exothermic and releases energy, photosynthesis is endothermic and absorbed energy.
Photosynthesis and respiration are the two metabolic reactions opposite to each other. Photosynthesis takes place only in the gree parts of the plant body having chlorophyll, whereas respiration takes place in all the living cells of plants and animals. Mitochondria are the cellular organelles where respiration takes place while the organelles for photosynthesis re chloroplasts. Photosynthesis takes place during the day time only, whereas respiration takes place day and night. In photosynthesis body weight is increased but in respiration weight is decreased. Respiration is an oxidation reaction whereas photosynthesis is a reduction reaction and can be well understood by comparing their chemical reactions.
(Diagram)
Chemical Equation in Respiration
Glucose + Oxygen ——-> Carbon dioxide + Water + Energy (In presence of mitochondria and enzymes)
Chemical Equation In Photosynthesis
Carbon dioxide + Water ——–> Glucose + Oxygen (In presence of chloroplast and solar energy)
Respiratory Organs of Insects
The respiratory system of insects is called the Tracheal system. It is a network of interconnecting air filled tubes called trachea delivering air directly to the body tissue cells. Trachea open outside through pores called spiracles.
Each trachea has chitinous cuticle lining which prevents it from collapsing.
A pair of spiracles is usually located on the sides of each segment of the thorax and abdomen. Spiracles have valves to open or close them regulated by special muscles. This controls water loss from internal body tissue.
(Diagram)
Trachea break up into numerous smaller tubes called tracheoles which ramify among the body tissues ending blindly. Tracheoles lack a chitinous lining. At rest the tracheoles are filled with watery fluid through which gaseous exchange tkes place in dissolved state.
Ventilation is brought about by contraction and relaxation of abdominal muscles which result in a rhythmic pumping of air into and out of the trachea.
Gas exchange takes place in tracheoles which are permeable to gases and are filled with a fluid in contact with the body tissue. Since oxygen diffuses directly into the tissue cells, blood of insects does not have hemoglobin so it is white. However, removal of carbon dioxide is dependent on blood plasma which takes it up for removal via spiracles.

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Introduction to Chemistry

Introduction to Chemistry

June 14, 2010 No Comment

CHAPTER – 1
Chemistry
The branch of science which deals with the composition and properties of matter, changes in matter and the laws or principles which govern these changes is called Chemistry.
Branches of Chemistry
Physical Chemistry
The branch of chemistry which deals with the physical properties and physical behavior of material things is called physical chemistry.
Inorganic Chemistry
The study of all elements and their compounds except carbon is called inorganic chemistry.
Organic Chemistry
The branch of chemistry in which we study the compounds of carbon is called organic chemistry.
Analytical Chemistry
The branch of chemistry which discusses the analytical methods for getting information about chemical compounds and chemical processes is called analytical chemistry.
Biochemistry
The study of chemical compounds present in living things is called biochemistry.
Industrial Chemistry
The application of chemical knowledge in technology and industry and the preparation of industrial products are called industrial chemistry.
Steps Involved in Getting Information in the Scientific Method
Science is not only an integrated knowledge of physical and biological phenomena but also the methodology through which this knowledge is gathered. The process of scientific discoveries is a cyclic process.
In science the facts are gathered through observations and experiments and then theories or law are deduced. The scientific method include following four steps:
1. Observation
2. Inference
3. Prediction
4. Experiment
1. Observation
The observations are made by the five senses of man. Men made equipments are also used for making observations. For example microscope is used for observing minute objects. Thermometer is used to measure temperature. Sensitive balance is used to determine the mass of a very light object. The capacity of man made instruments is also limited. But it can be improved by improving technology. Thus better and more reliable information are given to the scientists who produce better result. Information acquired through careful observations are called facts. These facts are foundation of scientific knowledge.
2. Inference
The facts gathered through observations are carefully arranged and properly classified. Correlating the knowledge thus acquired with previous knowledge, we try to think of a tentative solution to explain the observed phenomenon. The tentative solution is called hypothesis. The validity of this hypothesis is tested through the results obtained from experiments. The results are discussed by the scientists and the hypothesis is accepted or rejected. The accepted hypothesis then takes the form of theory. A theory when repeatedly gives the same results after experimentation and gives correct explanation of the scientific facts becomes a law or principle.
A theory remains valid until contrary informations are given on the basis of experimentation. Thus a hypothesis requires experimental support. But Avogadro’s hypothesis has been accepted as law without any experimental support.
3. Prediction
Facts, theories and laws which are deduced from observation can help in deducing more facts and phenomenon. This process is called prediction.
4. Experiment
An experiment is an integrated activity, which is performed under suitable conditions with specially designed instruments to get the required information. Such information is used to test the validity of the hypothesis. If a hypothesis is proved correct. It increases the reliability of known facts. If it is proved wrong, it stil can give information which can be used to deduce other results.
Chemistry and Society
Chemistry has played important role for well being of mankind in the form of food, clothing, shelter, medical treatment and chemical fertilizers, crops protected by insecticides, refined food and production of artificial fiber. Production of cement, iron bricks, glass, paint etc are all due to chemistry.
The hazards of chemistry are so vast that no aspect of human life has remained unaffected. The smoke coming from chimneys of chemial industries and from vehicles pollute the air. It is very dangerous to breath in that air. Similarly waste water from industry, pollute canals, rivers and has bad effect on land. Excessive chemical spray on plants also has bad effect.

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Chemical Combinations and Chemical Equations

Chemical Combinations and Chemical Equations

June 14, 2010 No Comment

CHAPTER – 2
Laws of Chemical Combinations
There are four laws of chemical combinations these laws explained the general feature of chemical change. These laws are:
1. Law of Conservation of Mass
2. Law of Definite Proportions
3. Law of Multiple Proportions
4. Law Reciprocal Proportions
Antoine Lavoiser has rejected the worn out ideas about the changes that take place during a chemical reaction. He made careful quantitative measurements in chemical reactions and established that mass is neither created nor nor destroyed in a chemical change.
1. Law of Conservation of Mass
Statement
It is presented by Lavoiser. It is defined as:
“Mass is neither created nor destroyed during a chemical reaction but it only changes from one form to another form.”

In a chemical reaction, reactants are converted to products. But the total mass of the reactants and products remains the same. The following experiment easily proves law of conservation of mass.
Practical Verification (Landolt Experiment)
German chemist H. Landolt, studied about fifteen different chemical reactions with a great skill, to test the validity of the law of conservation of mass. For this, he took H.shaped tube and filled the two limbs A and B, with silver nitrate (AgNO3) in limb A and Hydrochloric Acid (HCl) in limb B. The tube was sealed so that material could not escape outside. The tube was weighed initially in a vertical position so that the solution should not intermix with each other. The reactant were mixed by inverting and shaking the tube. The tube was weighed after mixing (on the formation of white precipitate of AgCl). He observed that weight remains same.
HCl + AgNO3 ———-> AgCl + NaNO3
2. Law of Definite Proportions
Statement
It is presented by Proust. It is defined as:
“When different elements combine to give a pure compound, the ratio between the masses of these elements will always remain the same.”

Proust proved experimentally that compound obtained from difference source will always contain same elements combined together in fixed proportions.
Example
Water can be obtained from different sources such as river, ocean, well, canal, tube well, rain or by the chemical combination of hydrogen and oxygen. If different samples of water are analyzed, it will have two elements, hydrogen and oxygen and the ratio between their mass is 1:8.
3. Law of Multiple Proportions
Statement
This law is defined as:
“When two elements combine to give more than one compounds, the different masses of one element, which will combine with the fixed mass of other element, will be in simple whole number ratio.”

Two different elements can combine to form more than one compound. They can do so by combining in different ratios to give different compounds.
Example
Hydrogen and oxygen combine with one another to form water (H2O) and hydrogen peroxide (H2O2). In water and hydrogen oxide 2 g of hydrogen combine with 16g and 32g of oxygen respectively. According to law of multiple proportions, the different masses of oxygen (16g and 32g) which have reacted with fixed mass (2g) of hydrogen will have a simple ratio between each other i.e. 16:32 or 1:2. It means that hydrogen peroxide contains double the number of oxygen atoms than water. This law proves this point of Dalton’s Atomic Theory that atoms do not break in a chemical reaction.
4. Law of Reciprocal Proportions
Statement
This law is defined as:
“When two element A, B combine separately, with the mixed mass of the third element E, the ratio in which these elements combine with E is either the same or simple multiple of the ratio in which A and B combine with each other.”

Example
Hydrogen and Nitrogen separately combine to form ammonia (NH3) and dinitrogen oxide (N2O), in these compounds, fixed mass of nitrogen is 14g and combines with 8 g of oxygen and 3 g of hydrogen. The ratio between the mass of oxygen and hydrogen is 8:3. Hydrogen and oxygen also combine with one another to form water (H2O). The ratio between hydrogen and oxygen in water is 16:2. These ratios are not same. Let us observe whether these ratios are simple multiple to each other or not following mathematical operation is carried out.
8:3 ::16:2
8/3 : 16/2
or
8/3 x 2/16
or
1/3 => 1:3
Definitions
Atomic Mass
The mass of an atom of the element relative to the mass of some reference or standard element is called atomic mass. Atoms are very small particles. They have very small mass. If the masses of atoms were to be expressed in gram. It is a very big unit for this very tiny object. Then it was decided by the chemists that masses of the atoms were to be found after comparing with mass to some standard form.
Hydrogen being the lightest element is taken as standard. The mass of the hydrogen atom taken as one.
The atomic mass could be defined as

“Atomic mass of an element is the mass of an atom of that element as compared to the mass of an atom of hydrogen taken as one.”

Example
The atomic mass of sodium is 23. It means that an atom of sodium is 23 times heavier than hydrogen atom. Similarly atomic mass of oxygen is 16. It means that an atom of oxygen is 16 times heaviest than that of hydrogen.
Atom
The smallest particle of an element which cannot exist independently and take part in a chemical reaction is known as Atom.

Examples
Hexogen(H), Carbon (C), Sodium (Na), Gold (Au) etc.
Molecule
The particle of a substance (Element or Compound) which can exist independently and show all the properties of that substance is called molecule.

Atoms of the same or different elements react with each other and form molecule.
Atoms of some elements can exist independently, since they have property of molecule so they are called mono atomic molecule.
Examples
Examples of Molecules of the elements are Hydrogen (H2). Nitrogen (N2), Sulphur (S8) etc.
Molecules of different elements are called compounds. For example HCl, H2O, CH4 etc.
Valency
The combining capacity of all elements with other elements is called valency.

Example
H = 1
C = 4
Al = 3
Mg = 2
Na = 1
Chemical Formula
“A brief name used for full chemical name at a compound is called Chemical Formula.”

A chemical formula is used to represent an element or a compound in terms of symbols. It also represents the number and type of atoms of elements present in the smallest unit of that substance.
Example
The chemical formula of hydrogen sulphide is H2S. It shows two types of elements (H and S) and number of atoms of element (2H and 1S). Similarly the formula of NaCl show number and type of different atoms present in its smallest unit.
Empirical Formula
“The formula which shows the minimum (simple) ratio between atoms present in a compound is known as Empirical Formula.”

Example
For example the empirical formula of hydrogen peroxide is HO that of water is H2O and benzene is CH.
Molecular Formula
The formula of an element or a compound which represents the actual number of atoms present in the molecule of these substances is called molecular formula.

Example
Water, Hydrogen Peroxide, Ethylene Benzene and Sulphur have molecular formula H2O, H2O2, C2H4, C6H6 and S8 respectively.
Molecular Mass
Molecular mass of an element or a compound is defined as the mass of its molecule relative to 1/12th of the mass of C-12. It is the sum of the atomic masses of all the atoms presents in its molecular formula.
Example
Molecular mass of water (H2O) = 2 + 16 = 18 a.m.u
Mass of hydrogen sulphide (H2S) = 2 + 32 = 34 a.m.u
Formula Mass
Formula mass of a compound is the mass of its formula unit relative to 1/12th of the mass of C-12.

Example
Formula mass of Sodium Chloride NaCl = 23 + 35.5 = 58.5 a.m.u
Formula mass of Calcium Chloride CaCl2 = 40 + 35.5×2 = 111a.m.u
Molar Mass
The mass of one mole of a substance is called molar mass.
Example
1 mole of Hydrogen atom (H) = 1.008g
1 mole of Hydrogen molecule (H2) = 2.016g
Thus mass of substance is related to the particles by mole.
Chemical Reaction
A chemical change in which reactants are converted to products is called chemical reaction.
Zn + 2HCl ——–> ZnCl2 + H2
The fact that a chemical reaction is taking place can be inferred from the following observation.
1. Evolution of a gas
2. Change in colour
3. Change in temperature.
4. Emission of light.
Types of Chemical Reaction
The chemical reaction is classified into following types:
1. Displacement Reaction
The reaction in which an atom or group of atoms is displaced by another atom or group of atoms in a compound is called displacement reaction.
Fe + CuO ———> Cu + FeO
2. Double Displacement Reactions
The reactions in which reacting substances exchange their radicals or ions are double displacement reaction. Insoluble salts are formed by mixing soluble salts.
3. Addition Reactions
When two different compounds or elements react together to give only one confound, the reaction will be called addition reaction.
2Mg + O2 ——–> 2MgO
4. Decomposition Reaction
The reaction in which some compounds may decompose into elements or simpler compounds on heating is called decomposition reaction.
CaCO3 ———> CaO + CO2 (Heat)
Chemical Equation
Symbolic representation of chemical change in terms of symbols and formulae is called Chemical Equation.

Method of Equation Writing
A chemical equation can be written as follows:
1. Write the formulae and symbols of the reactants on the left hand side.
2. Write the formulae and sympols of the products on the right hand side.
3. Separate the reactants and products by an arrow which is directed towards the products.
Characteristics of Chemical Equation
1. Chemical equation must be representative of a chemical reaction.
2. It should represent molar quantities.
3. It should be balanced in terms of atoms/molecules of reactants and products.
Reactants
Those substances, which react together in a chemical reaction, are called reactants.
Zn + 2HCl ——> ZnCl2 + H2
In the above reaction Zn and HCl are the reactants.
Products
Those substances, which are formed in a chemical reaction, are called products.
Zn + 2HCl ——> ZnCl2 + H2
In the above reaction, ZnCl2 and H2 are products.
Information obtained from a Chemical Equation
1. A balanced equation indicates that which reactant undergo chemical change. It indicates that which products are formed.
2. It indicates that how many moles of reactants under go chemical change. It indicates that how many moles of products are formed.
Why are Chemical Equations Balanced
A chemical equation must be balanced in order to satisfy the law of conservation of matter, which states that matter can neither be created nor be destroyed during a chemical reaction.

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Atomic Structure

Atomic Structure

June 14, 2010 No Comment

CHAPTER – 3
Dalton’s Atomic Theory
The important postulates of Dalton’s atomic theory are:
1. All elements are composed of atoms. Atom is too small so that it could not be divided into further simpler components.
2. Atom cannot be destroyed or produced.
3. Atoms of an element are similar in all respects. They have same mass and properties.
4. Atoms of different elements combine in a definite simple ratio to produce compounds.
Discovery of Electron
A discharge tube is a glass tube. It has two electrode, a source of electric current and a vacuum pump.
(Diagram)
Sir William Crooks (1895 performed experiments by passing electric current through gas in the discharge tube at very low pressure. He observed that at 10-4 (-4 is power to 10) atmosphere pressure, shining rays are emitted from cathode. These rays were named cathode rays. Cathode rays are material particles as they have mass and momentum.
Properties of Cathode Rays
The properties of these particles are given below:
1. These particles are emitted from cathode surface and move in straight line.
2. The temperature of the object rises on which they fall.
3. They produce shadow of opaque object placed in their path.
4. These particles are deflected in electric and magnetic fields.
5. These particles are deflected towards positive plate of electric field.
Discovery of Proton
Gold Stein (1886) observed that in addition to the cathode rays, another type of rays were present in the discharge tube. These rays travel in a direction opposite to cathode rays. These rays were named positive rays. By using perforated cathode in the discharge tube the properties of these rays can be studied. Positive rays are also composed of metered particles. The positive rays are not emitted from anode. They are produced by the ionization of residual gas molecules in the discharge tube. When cathode rays strike with gas molecule, electrons are removed and positive particles are produced.
Properties of Positive Rays
1. They are deflected towards negative plate of electric field. Therefore these rays carry positive charge.
2. The mass of positive rays is equal to the mass of the gas enclosed in the discharge tube.
3. The minimum mass of positive particles is equal to the mass of hydrogen ion (H+). These positive ions are called Protons.
4. The charge on proton is equal to +1.602×10-19 Coulomb. (-19 is power of 10)
Natural Radioactivity
The phenomenon in which certain elements emit radiation which can cause fogging of photographic plate is called natural radioactivity. The elements which omit these rays are called radioactive elements like Uranium, Thorium, Radium etc. There are about 40 radioactive elements. Henri Bequrel (1896) discovered radioactivity.Madam Curei also has valuable contribution in this field.
In natural radioactivity nuclei of elements are broken and element converted to other elements. Natural radioactivity is nuclear property of the elements.
Alpha Rays
1. They are helium nuclei. They are doubly positively charged, He2+.
2. They move with speed equal to the 1/10th of the velocity of the light.
3. They cannot pass through thick-metal foil.
4. They are very good ionizer of a gas.
5. They affect the photographic plate.
Beta Rays
1. They are negatively charged.
2. They move with the speed equal to the velocity of light.
3. They can pass through a few millimeter thick metal sheets.
4. They are good ionizer of a gas.
5. They can affect the photographic plate.
Gamma Rays
1. They are electromagnetic radiations.
2. They travel with speed equal to velocity of light.
3. They carry no charge.
4. They have high penetration power than alpha and beta rays.
5. They are weak ionizer of gas.
Rutherford Experiment and Discovery of Nucleus
Lord Rutherford (1911) and his coworkers performed an experiment. They bombarded a very thin, gold fail with Alpha particles from a radioactive source. They observed that most of the particles passed straight through the foil undeflected. But a few particles were deflected at different angles. One out of 4000 Alpha particles was deflected at an angle greater than 150.
(Diagram)
Conclusion
Following conclusions were drawn from the Rutherford’s Alpha Particles scattering experiment.
1. The fact that majority of the particles went through the foil undeflected shows that most of the space occupied by an atom is empty.
2. The deflection of a few particles over a wide angle of 150 degrees shows that these particles strike with heavy body having positive charge.
3. The heavy positively charged central part of the atom is called nucleus.
4. Nearly all of the mass of atom is concentrated in the nucleus.
5. The size of the nucleus is very small as compared with the size of atom.
Defects of Rutherford Model
Rutherford model of an atom resembles our solar system. It has following defects:
1. According to classical electromagnetic theory, electron being charged body will emit energy continuously. Thus the orbit of the revolving electron becomes smaller and smaller until it would fall into the nucleus and atomic structure would collapse.
2. If revolving electron emits energy continuously then there should be a continuous spectrum but a line spectrum is obtained.
(Diagram)
Bohr’s Atomic Model
Neil Bohr (1913) presented a model of atom which has removed the defects of Rutherford Model. This model was developed for hydrogen atom which has only proton in the nucleus and one electron is revolving around it.
Postulates of Bohr’s Atomic Model
The main postulates of Bohr’s Model are given below:
1. Electrons revolve around the nucleus in a fixed orbit.
2. As long as electron revolves in a fixed orbit it does not emit and absorb energy. Hence energy of electron remains constant.
3. The orbit nearest to the nucleus is the first orbit and has lowest energy. When an electron absorbs energy it jumps from lower energy orbit to higher energy orbit. Energy is emitted in the form of radiations, when an electron jumps from higher energy orbit to lower energy orbit. The unit of energy emitted in the form of radiations is called quantum. It explains the formation of atomic spectrum.
4. The change in energy is related with the quantum of radiation by the equation :
E2 – E1 = hv
where
E1 = Energy of first orbit
E2 = Energy of the second orbit
h = Planck’s constant
v = Frequency of radiation
Atomic Number
The number of protons present in the nucleus of an atom is called atomic number or proton number. It is denoted by z. The proton in the nucleus of an atom is equal to number of electrons revolving around its nucleus.
Mass Number
The total number of the protons and neutrons present in the nucleus of an atom is called mass number. The protons and neutrons together are called nucleon. Hence it is also known as nucleon number. It is denoted by A. the number of neutrons present in the nucleus of an atom is rperesented by N.
Mass Number = No of Protons + No of neutrons
A = Z + N
Isotopes
The atoms of same elements which have same atomic number but different mas number are called Isotopes. The number of protons present in the nucleus of an atom remains the same but number of neutrons may differ.
Isotopes of Different Elements
Isotopes of Hydrogen
Hydrogen has three isotopes:
1. Ordinary Hydrogen or Protium, H.
2. Heavy Hydrogen or Deutrium, D.
3. Radioactive Hydrogen or Tritium, T.
Protium
Ordinary naturally occurring hydrogen contains the largest percentage of protium. It is denoted by symbol H. It has one proton in its nucleus and one electron revolve around the nucleus.
Number of Protons = 1
Number of Electrons = 1
Number of Neutrons = 0
Atomic Number = 1
Mass Number = 1
Deutrium
Deutrium is called heavy hydrogen. The percentage of deutrium in naturally occuring hydrogen is about 0.0015%. It has one proton and one neutron in its nucleus. It has one electron revolving around its nucleus. It is denoted by symbol D.
Number of Proton = 1
Number of Electron = 1
Number of Neutrons = 1
Atomic Number = 1
Mass Number = 2
Tritium
Radioactive hydrogen is called tritium. It is denoted by symbol T. The number of tritium isotope is one in ten millions. It has one proton and 2 neutrons in its nucleus. It has one electron revolving around its nucleus.
Number of Proton = 1
Number of Electron = 1
Number of Neutron = 2
Atomic Number = 1
Mass Number = 3

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Periodicity of Elements and Periodic Table

Periodicity of Elements and Periodic Table

June 14, 2010 No Comment

CHAPTER – 4
Definitions
Periodic Table
A table of elements obtained by arranging them in order of their increasing atomic number in which elements having similar properties are placed in the same group is called Periodic Table.

Group
The vertical column of elements in the periodic table are called Groups.
Period
The horizontal rows of elements in the periodic table are called Periods.
Periodicity
The repetition of physical and chemical properties of elements periodically is called Periodicity of Properties.

Periodic Law
Physical and chemical properties of elements are periodic function of their atomic masses.

Metal
Elements which are good conductors of heat and electricity are malleable and ductile and have a metallic luster are called Metals like Sodium, Potassium, Gold, Copper etc.

Non-Metals
Elements which are non or bad conductor of heat and electricity are neither malleable or ductile and have no metallic luster are called Non-Metals like Carbon, Nitrogen, Chlorine etc.

Metalloids
Metalloids are semi metals have the properties which are intermediate between a metal and non-metal like Boron, Silicon, Germanium, Arsenic, Antimony etc.
Law of Triads
A German Chemist, Dobereiner (1829), arranged chemically similar elements in groups of three on the basis of their atomic masses called Triads and it was found that atomic mass of the middle element was approximately equal to the average of atomic masses of other two elements. This is known as Law of Triads.

Drawback or Defect
As very few elements could be arranged in such groups, this classification did not get wide acceptance.
Law of Octaves
An English Chemist Newland (1864) stated that if the elements were arranged in the ascending order of their atomic masses, every eight element will have similar properties to the first. This is knows as Law of Octaves.

Drawback or Defects
1. Noble gases were not discovered at that time and no place was reserved for the undiscovered noble gases.
2. In the same way no blank spaces for the undiscovered elements were present in his table.
Mendeleyv’s Period Table and Periodic Law
Russian Chemist, Mendeleyv’s (186) who wa working separately from Lother Mayer published a table of elements.
According to Mendeleyv’s when the element were arranged in order of their increasing atomic mases, the elements with similar properties were repeated after regular interval and were placed one above the other.A table obtained in this manner is called Periodic Table. Mendeleyv’s stated this periodicity in the form of Periodic Law.
Important Features of Mendeleyv’s Periodic Table
The important features of Mendeleyv’s Periodic table are:
Periods and Groups
The horizontal rows which run from left to right in Periodic Table are called Periods and they are twelve in number.
The vertical rows which run from top to bottom in periodic table are called groups and they are eight in number.
Vacant Spaces
Mendeleyv’s left many vacant spaces for the still unknown elements. For example, next to Calcium (40) should be Titanium (48) but it resembled silicon (28) instead of Aluminium (27). He left vacant space for element with atomic mass 44.
Discovery of New Element
Mendeleyv’s discovered new elements and also guessed their atomic mass and properties.
Atomic Mass Correction
Mendeleyv’s corrected the atomic masses of certain elements on basis of their properties and provided proper place to them in the periodic table.
Defects in Mendeleyv’s Periodic Table
The Mendeleyv’s Period Table has following defects:
Irregular Position of Some Elements
According to Mendeleyv’s Periodic Law Potassium (39) should be placed before Argon (40) but he placed Argon (40) before Potassium (39) which goes against his law.
Position of Isotopes
Mendeleyv’s periodic table gives no indication about the position of isotopes.
Structure of Atom
Mendeleyv’s Periodic table gives no idea about structure of atoms.
Position of Lanthanides and Actinides
Lanthanides and Actinides have not been given proper place in Periodic Table.
Coinage and Alkali Metals
Alkali metals and coinage metals with different properties are placed in the same group. This defect has been replaced by placing them into two sub groups.
Modern Periodic Law and Modern Periodic Table
Modern Periodic Law
Physical and chemical properties of the elements are periodic function of their atomic number. Mosely (1913) says that atomic mas is not fundamental property. Due to some defects present in Mendeleyv’s periodic law, Mosely introduced the concept of anomic number for the elements.
Example
When isotopes were discovered, it was thought advisable to arrange the elements on basis of their atomic number instead o increasing atomic mases. Isotopes were needed different position in the Mendeleyv’s periodic table. Hence Mendeleyv’s periodic law was modified.
Modern Periodic Table
When Mendeleyv’s periodic law was modified and new elements were discovered. This forcd the scientists to change Mendeleyv’s periodic law.
The electronic configuration of atoms also played an important role in he arrangement of the modern periodic law. This form of periodic table is called “Long form of Periodic Table” because it contains eighteen groups instead of eight but seven periods instead of twelve.
Group I – The Alkali Metals
The elements of group I are called “Alkali Metals”. The word alkali is derived from an Arabic word meaning Ashes.
Elements of Group I
Lithium
Sodium
Potassium
Rubidium
Cesium
Francium
Properties of Group I
1. They are mono atomic.
2. They exist in solid metallic state.
3. Outer most shell of these elements is incomplete having one electron.
4. Elements of this group are highly reactive.
5. Elements of this group have large tendency to form compounds.
6. Elements of this group are strongly electro-positive.
Group II – The Alkaline Earth Metals
The elements of group II are called Alkaline Earth Metals. These elements occur in nature as silicate mineral and their oxides and hydroxides are strongly basic. Therefore these elements are called Alkaline Earth Metals.
Elements of Group II
Beryllium
Magnesium
Calcium
Strontium
Barium
Radium
Properties of Group II
1. They are mono atomic.
2. They exist in solid state.
3. Outer most shell of these elements is incomplete having two electrons.
4. Elements of this group are moderately reactive.
5. Elements of this group have moderate tendency to form compounds.
Group III – The Boron or Aluminium Family
The elements of group III exist in solid state.
Elements of Group III
Boron Metalloid
Aluminium Metal
Gallium Metal
Indium Metal
Thallium Metal
Properties of Group III
1. They are mono atomic.
2. They exist in solid state.
3. Outer most shell of these elements is incomplete having three electrons.
4. Elements of this group are quite reactive.
5. Elements of this group have moderate tendency to form compounds.
Group IV – The Carbon and Silicon Family
Elements of Group IV
Carbon
Silicon
Germanium
Tin
Lead
Properties of Group IV
1. They are mono atomic.
2. They exist in solid state.
3. Outermost shell of these elements is incomplete.
4. Elements of this group are quite reactive.
5. Elements of this group have moderate tendency to form compounds.
Group V – The Nitrogen Family
Elements of Group V
Nitrogen
Phosphorus
Arsenic
Antimony
Bismuth
Properties of Group V
1. Some are mono atomic and some are di-atomic.
2. Some of them exist in gaseous and some are in solid state.
3. Outermost shell of these elements is incomplete having five electrons.
4. elements of this group are quite reactive.
5. Elements of this group have quite tendency to form compound.
Group VI – The Oxygen Family
Elements of Group VI
Oxygen
Sulphur
Selenium
Tellurium
Polonium
Properties of Group VI
1. Some are mono atomic and some are di-atomic.
2. Some of them exist in gaseous and some are in solid state.
3. Elements of this group have quite tendency to form compounds.
4. The tendency of forming covalent bond decreases from oxygen to polonium.
5. There is a gradual decrease in the ionization potential down the group.
Group VII – The Halogen Family
Elements of Group VII
Fluorine Gas
Chlorine Gas
Bromine Liquid
Iodine Solid
Astatine Radioactive
Properties of Group VII
1. They are diatomic except At.
2. Halogens are very active non-metals.
3. Outer most shell of these elements is incomplete having seven electrons.
4. Elements of this group are highly reactive.
5. There is a gradual decrease in the ionization potential down the group.
Transition Elements
Definition
Elements in Group IB, IIB, through VIIB are known as Transition Elements because they show their properties which are transitional between higly reactive and strong electro-positive elements of S-block which form ionic compounds and p-block elements which form largely covalent compounds.
Properties of Transition Elements
1. Transition Elements have incomplete inner electron shells.
2. They show variable valency.
3. They show similar behaviour.
4. They all are metals.
5. They have strong inner atomic bonds.
Group 0, The Noble Gases
The elements of Group VIII A are called “Noble Gases” or “Inert Gases” or “Zero Group Elements”.

Elements of Group 0
Helium
Neon
Argon
Krypton
Xenon
Radon
Properties of Group 0
1. They are mono atomic.
2. They exist in gaseous state.
3. Outer most shell of these elements is either complete or contains eight electrons.
4. These elements are mostly chemically non-reactive.
5. These elements have no tendency to form compounds (only a few of these compounds are known).
Atomic Radius
Definition
One half of the distance between the nucleus of two identical atoms when these are in close contact with each other is called Atomic Radius.

Unit
It is measured in angstrom unit A.
Trend in Period
The atomic radii decreases from left to right within a period in the periodic table. This is because nuclear charge increases with the increase of atomic number. But the number of shells remains same within a period.
Trend in Group
Atomic radius increases from top to bottom in a group. This is because, although nuclear charge increases from top to bottom but at the same time on new shell is also added for each successive element down the group.
Ionization Energy (I.E) or Ionization Potential (I.P)
Definition
The minimum energy needed to remove an electron from an isolated, gaseous atom in its ground state is called Ionization Energy.
Unit
It is expressed in electron volts or kilo-joules permole.
1 ev = 96.49kj
Factors Affecting Ionization Energy
The ionization energy of elements depends upon the following factors:
1. Effect of Nuclear Charge on I.E
The greater the nuclear charge the higher is the ionization energy.
2. Effect of Atomic Size
The larger the size of atom the lower is the ionization energy.
Trend of I.E in Period
Ionization energy increases from left to right in a period due to increase in nuclear change and decrease in atomic size.
Trend of I.E in Group
I.E decreases from top to bottom in a group due to increase in atomic size.
Electronegativity
Definition
The tendency of each atom in a covalent molecule to attract a shared pair of electrons towards itself is known as its electronegativity.
Factors Affecting Electronegativity
Electronegativity depends upon the following factors:
Atomic size
Atomic Number
Electron Affinity
Ionization Energy
Trend or Variation in the Period
Electronegativity increases from left to right within a period due to increase in nuclear charge and decrease in atomic size.
Trend or Variation in the Group
Electronegativity values decreases from top to bottom within a group due to increase in atomic size.
Electron Affinity
Definition
The energy change that occurs when an electron is gained by an atom in the gaseous state is known as Electron Affinity.
Electron Affinity for the addition of first electron is negative i.e. energy is released but for further addition of electrons it is positive because energy has to be added to over come repulsion between negative ion and electron.
Unit
It is measured in KJ/mol or in e.v per atom.
Factors Affecting Electron Affinity
Atomic Size
Nuclear Charge
Trend or Variation of Electron Affinity in Group
Down the group in the periodic table, electron affinity decreases because the addition of a new shell to each atom decreases its force of attraction.
Trend or Variation of Electron Affinity in Period
In a period, the electron affinity increases from left to right because the incoming successive atoms have higher nuclear charge and attract electron more towards itself.

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States of Matter

States of Matter

June 14, 2010 No Comment

CHAPTER – 6
States of Matter
Matter has three states:
1. Gas
2. Liquid
3. solid
These are physical states of matter. The three states of one matter may have different physical properties while their chemical properties are same. Water exists in three physical states solid (ice), liquid and gas(steam) has same chemical properties.
Kinetic Theory of Matter
The Kinetic theory was presented to explain the properties of gases and is called kinetic theory of gases. But this theory was also able to explain the composition of liquid and solid state of matter. So its is called Kinetic Theory of Matter.
According to Kinetic Theory of matter:
1. All matter is composed of atoms, molecules or ions.
2. These particles have kinetic energy due to which they are in the state of motion.
3. In gaseous state, these particles move in a straight line. They collide with one another and with the walls of container. In liquids the rate of their movement is very small but in solids, there is to and fro motion only.
4. Generally material particles can have three types of movements, i.e. translational, rotational and vibrational.
Solids
The state of matter which has definite shape and volume is called solid.
Properties of Solids
1. Definite Volume and Shape
The cohesive forces in solid substances are so strong that they keep their particles arranged in fixed positions. So due to restrict movements of particles, the solids have definite volume and shape.
2.Motion of Particles
The solid particles have vibrational motion only because these particles are held in fixed position by strong cohesive forces.
3. Effect of Heat
The physical state of solid substance can be changed by heating. On heating solid is converted to liquid and gaseous state. Heat increases the kinetic energy of the particles and they start vibrating at higher frequency. At a particular temperature the vibrational motions become fast that they overcome the cohesive forces and solid melts to liquid.
4. Melting Point
The temperature at which the solid is converted to liquid on heating is called melting point. At melting point, the particles of solid loose their means position and their arrangement. The solid collapses and turns to liquid.
5. Sublimation
The conversion of some solids directly into gaseous state on heating is called sublimation. Iodine, ammonium chloride and naphthalene change directly into vapour state upon heating.
Liquid
The state of matter having definite volume but indefinite shape is called liquid.
Properties of Liquid
1. Volume
Liquids have definite volume. In liquid particles are very close to one another and have cohesive forces among the particles. Due to the presence of cohesive forces, liquids have definite volume and keep their level as well.
2. Shape
Liquids do not have any specific shape. They adopt the shape of the container. The molecules of liquid are able to move. Due to this random motion the molecules of liquid do not have fixed position and as a result, a liquid does not have any specific shape.
3. Evaporation
Conversion of liquid into its vapours at any temperature is called evaporation. The molecules of liquid come to the surface of liquid and escape by overcoming cohesive forces. So liquid is converted to vapours at all temperature.
4. Boiling Point
The temperature of a liquid at which its vapour pressure becomes equal to the atmospheric pressure is called boiling point.
Gas
The state of matter which does not have definite shape and volume is called gaseous state.
Properties of Gaseous State
1. Indefinite Volume and Shape
In gaseous state, the molecules have insignificant cohesive forces among themselves. They move very fast in all possible directions. As a result, a gas neither has fixed shape nor a fixed volume.
2. Kinetic Energy of the Particle of a Gas
Gas particles have very high kinetic energy as compared to liquid and solid state.
3. Pressure
The molecules of a gas are in the state of random motion. The molecules of gas not only collide with one another but also with the walls of the container in which they are enclosed. Due to their collision, the velocity of the molecules changes every moment. The pressure exerted by gas is also due to the collision of its molecules with the walls of the container.
4. Elastic Collision
The collision of gas molecules is elastic in nature which means that the total energy of the colliding molecules remains the same before and after the collision.
5. Kinetic Energy
The kinetic energy of molecules of gas is very high as compared with solid and liquid.
Diffusion
The movement of molecules from a higher concentration to a lower concentration is known as Diffusion.
If the concentration of molecules at a particular place is higher, they start moving towards a place where their concentration is lower. When the concentration of molecules at both the places becomes equal the process of diffusion stops.
Diffusion in Gases
The molecules of one gas can diffuse easily into the molecules of other gas. For example if an open bottle of a perfume is kept in a room, its smell will spread uniformly throughout the room. The liquid perfume present in the bottle volatilized slowly and its vapours diffuse through out the room.
Graham’s Law of Diffusion
Scottish Chemist, Thomas Graham (1833) discovered that lighter gs can diffuse through porous pot faster than the heavier one. This is called Graham’s
Law of Diffusion.
Hydrogen being lighter gas will diffuse faster than oxygen or carbon dioxide.
Diffusion in Liquids
Liquid molecules can also diffuse because they have free movement. Since the molecules of liquid move comparatively slowly than gas molecule, their rate of diffusion are also lesser than gases.
Brownian Movement
Robert Brown (1927) discovered this phenomenon:
The free movement of the molecules of gases and liquid is called Brownian Movement.”

When a pollen grain is put in water. The movement of pollen grain in water is observed by microscope. It is observed that pollen grain is continuously moving in all directions. This free movement of pollen grain was due to the free movement of water molecules. The colliding water molecules will also force pollen grain to move as well. The students can observe Brownian movement with the help of simple experiment.
Experiment
Put a drop of milk on a microscope slide and cover it with cover slip. Put it under microscope and observe it. You will see small particle of fat moving randomly in milk. The movement of fat particles is actually due to the movement of water molecules in milk.

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