Atoms Molecules and Elements

• Ionic bond
• Covalent bond
• Coordinate bond

Ionic Bond:

• An atom forms a bond to complete its octet i.e. attain 8 electrons in its outer most shell or valence shell.
• An ionic bond is formed between a metal and a non-metal. A metal atom loses electrons and a non-metal atom gains electrons for completion of their octet forming cations and anions respectively.
• The electrostatic force of attraction between the positive and negative charged ions brings the particles together forming an ionic compound.

• A chemical formula of a compound represents the composition of a molecule of the substance in terms of the symbols of the elements present in the molecule.

Formulae of Elements:

• The chemical formula of an element is a symbolic representation of element the subscript if present tells about the number of atoms present in the molecule.

For example:

H₂  2 atoms of Hydrogen in one molecule

N₂  2 atoms of Nitrogen in one molecule

O₂  2 atoms of Oxygen in one molecule

• Radical is an atom group of atoms of elements that carries a charge (positive or negative) and behaves as a single unit in the reaction.

Example:

Sulphate ion SO₄^2– is a radical

H₂SO₄ + 2NaCl → Na₂SO₄ + 2HCl

The sulphate part in H₂SO₄ moves as a unit and combines with sodium.