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Air as a Mixture |
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As we know that we cannot live without air even for a single minute. We live in a vast ocean of air, which extends upwards for over 1000 km. Apart from providing us air to breathe, this blanket of air traps the sun's heat that is essential for life on the earth, and also acts as a barrier against harmful and excessive radiation. The lowest part of this ocean of air is known as the troposphere. It contains about 75% of the total mass of the atmosphere and 90% of water vapour. It is in this troposphere, where all the weather is formed. |
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Structure of Atom |
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A story unfolds - Structure of atom : Let us right away meet those who scripted a "mighty story" of a "miniscule" atom.
John Dalton (1766 - 1844) : Born in a poor family of a weaver in England, he rose to become a teacher and later a Principal of a school. In 1793, he left for Manchester to teach physics and chemistry in a college. |
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Coal and Petroleum |
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Man's quest for sources of energy is inexhaustible. Early man depended mainly on muscular energy and later began to use wind and flowing water as sources of energy. He learned the art of making and controlling fire. Fire became his source of light at night. He used fire for warmth and realized that cooked food tastes better than raw food. As civilization advanced, man started using fire in making weapons, pottery etc. Today, with the progress in science and technology, fuels have become indispensable to man. |
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Chemical Reactions |
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There are just 26 alphabets in English language, but the number of words are innumerable. You have studied about the 115 known elements and how they are classified for systematic and comprehensive study. Thousands of compounds are born by various chemical reactions involving these elements. |
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Elements, Compounds and Mixtures |
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All matter can be broadly divided into two major groups "Pure" and "Impure". The term 'purity' has quite a different meaning in chemistry than in our day-to-day life. Normally when we refer to pure water, pure milk, etc., what is implied is that the water, milk etc., are free from harmful substances such as bacteria, fungi, viruses, etc. 'Purity' in chemistry is entirely of a different nature. When we say a substance is pure, it means that the substance is made of only one type of constituent particles. |
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Group 1 (IA) Element - Hydrogen |
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Hydrogen is the lightest substance known and the most abundant element in the universe. It has a mass of just 0.09 g per litre at normal temperature and pressure. Though it is present in abundance in celestial bodies, like the sun and stars, it is not present in a free state in our atmosphere. Hydrogen is present in the combined form in many substances, like water, acids, alkalis, hydrocarbons, carbohydrates, fats and oils, proteins, cellulose, etc. |
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Group 14 (IVA) Element - Carbon |
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Carbon is an extremely important element and was known from the earliest times in the form of charcoal, soot, etc. Although the amount of carbon in the earth's crust is only eleventh by mass, it ranks as high as oxygen and hydrogen, in importance. In nature, it occurs mainly as coal and petroleum and in the form of calcium carbonate or magnesium carbonate rocks (calcite, limestone, dolomite, marble and chalk). It is also present in almost all the foods we eat. Thus, millions of carbon compounds exist in nature and many thousands are synthetically prepared. |
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Group 15 (VA) Element - Nitrogen |
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Daniel Rutherford, a Scottish Physician, discovered nitrogen in 1772. But it was Lavoisier, who proved that nitrogen is an element and that it was not a supporter of combustion and respiration. He called it 'azote' meaning 'no life'. The name 'Nitrogen' was given to it by Jean Antoine Chaptal (1756 - 1832), in the year 1790. |
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Group 16 (VIA) Elements-Oxygen and Sulphur |
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1. Oxygen is the first member of the group VIA and sulphur is the second member of the group VIA.
2. Other member of this group are selenium, tellurium and polonium. |
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Group 17 (VIIA) Element - Chlorine |
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The Swedish chemist Carl Wilhelm Scheele first prepared chlorine in 1770 by treating hot concentrated hydrochloric acid with manganese dioxide. |
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Language of Chemistry |
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A chemical equation is a "balanced account of a chemical transaction." In any chemical transaction or reaction, the number of atoms of all the participating elements will remain proportionately constant before and after the reaction (The Law of Conservation of Mass). |
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Nature of Matter |
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Intensive investigation by scientists over the years led to the development of a mental model known as 'dynamic particle model'. |
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Periodic Classification of Elements |
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In the famous atomic theory of John Dalton (1805), it was suggested that the atoms of an element have a characteristic mass. So, attempts were made to classify elements on the basis of their atomic masses. |
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Physical and Chemical Changes |
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Matter undergoes certain changes as a result of the application of energy. Glaciers melt in summer and rivers freeze in winter. Water from saltpans on the sea coast dry up, leaving behind salt. Water from the sea evaporates to from water vapor, which form into clouds and then condense to form rain. A candle upon burning gives light, heat, water vapor and carbon dioxide. Hydrogen burns in air to form water. |
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Chemical Bonding |
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Chemical bonding is like a glue that binds atoms together. And what goes into making that glue? Only electrons. Not all electrons make up the glue, it is only the valence electrons. Valence electrons are the outermost electrons [electrons in the last shell]. |
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Study of Carbon Monoxide and Carbon Dioxide |
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Carbon has a variable valency of 2 and 4, and as a result, produces two important kinds of oxides namely carbon monoxide and carbon dioxide. Both these oxides are gases at room temperature. |
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Study of Gas Laws |
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Gas is one of the three states of matter - the other two being liquid and solid. A gas differs from a solid and a liquid in a number of ways. A gas fills entire space available to it and therefore it has no definite shape or volume. |
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Water |
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Water is the only substance that can exist simultaneously in all the three states of matter, i.e., solid, liquid and gaseous on this earth,. A simple experiment shows the existence of all these three states together. Take a glass half packed with ice cubes and cover it. The ice starts melting. Water is now visible in two states in the glass: in the solid state of ice cubes and in the liquid state of water. |
