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What is an atom?


What is the composition of air?

Air cannot be seen, touched, or tasted, but it is much more than nothing. It is a mixture of various gases. Four-fifths of the air is nitrogen gas (N2) and one fifth of it is oxygen gas (O2). Another important component of air is carbon dioxide (CO2). We need oxygen to live and plants need carbon dioxide to live.


What is an atom?

The term ‘atom’ comes from Greek word atomos, meaning ‘indivisible’. Earlier, it was considered that atoms were the smallest units of a substance and could not be split further. Today, we know that atoms can be further split into smaller particles. An atom is made up of the atomic nucleus, which consists of positively charged protons and an equal number of neutrons, and atomic shells. These are occupied by negatively charged electrons, which move at high speeds around the atomic nucleus- like planets around the sun.


What is an element?

An element is a ‘pure substance’ consisting of atoms of the same kind. Elements cannot be broken down into substances, but they can combine with other elements to make new substances. Each element has a unique symbol, for example, ‘O’ means oxygen, ‘Na’, sodium (Latin: natruim) and ‘Cl’ means chlorine.  The number of protons in an atomic nucleus determines the element. This number is called the atomic number of the element.


What is a molecule?

A molecule consists of two or more atoms, which are held together by chemical bonds. A water molecule is made up of two atoms of hydrogen (H) and one atom of oxygen (O). Thus the chemical formula of water is H2O. Elements also frequently occur in molecular forms. For example two atoms of chlorine, oxygen and nitrogen combine to form Cl2, O2 and N2 respectively. There are complicated molecules as well, such as plastics and polymers.


What is a Gas?

Gas is one of the states of matter. In a gas, the forces that bind the elements together are not as strong as they are in liquids or solids. These forces are not to be confused with the forces of attraction within the molecules. These are transactions between the states of matter.  For instance, wax is solid at room temperature, melts when a candle is lit, and evaporates at a very high temperature.

The fourth state of matter, rarely found on earth, is plasma. In this state the matter is ‘ionized’ and conducts electricity.


What is a chemical reaction?

In a chemical reaction, a chemical change takes place. The reactants lose their properties, and the products formed usually have properties different from those of the reactants. For example, on igniting, grey iron or steel wool burns in air with a bright light and a blue-black substance remains as a residue, which is heavier than steel wool. In a combustion reaction, iron reacts with oxygen in the air. The new substance formed in the oxidation reaction is iron oxide. The term ‘oxidation’ is derived from the Latin word, ‘oxygenium’, meaning oxygen. The more easily electrons move from the outermost shell, the more reactive the substance is. Nobel gases such as argon and neon are not reactive. For this reason, we breathe in the same argon atoms today which dinosaurs breathed in.   





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