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| Formation of Molecule
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| Atoms of most of the elements do not exist independently. They either form molecules or ions.
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| An atom having a charge on it is called an ion. When an atom loses or gains charge, it gets converted into a positively or negatively charged ion respectively. Ions may consist of single charged atoms or a group of atoms that have a net charge on them.
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| Molecules are formed by combination of atoms or ions by chemically bonding to each other or held by attractive forces due to the charges.
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| A molecule is smallest particle of an element or compound, which is capable of independent existence.
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If the molecule is made up of atoms of the same element it is said to be homo-atomic. Examples: O2, N2
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If the molecule is made up of atoms of the different elements it is said to be hetero-atomic. Examples: CO2, H2O, SO3, HCl
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| Depending upon the number of atoms in one molecule of the element it can be classified as:
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| The number of atoms, which constitute one molecule of an element, is called its atomicity.
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| Phosphorus: P4 - 4 atomicity
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| Sulphur: S8 - 8 atomicity
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| Oxygen: O2 - 2 atomicity
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| Recently a different form of carbon - C60 has been discovered. It is named Buckministerfullerene and has an atomicity of sixty.
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| A molecule of a compound consists of two or more atoms of different elements joined together in a fixed ratio.
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| Examples: CuSO4 contains Cu - 1 atom, S - 1 atom, O - 4 atoms
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