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Ion formation:

i. Electrons revolve around the nucleus in particular orbits.

ii. Among the orbits, the outermost orbits participate in chemical reaction.

iii. Sometimes the outermost shell is incomplete which causes the giving and taking of electrons.

iv. In a chemical reaction, metals give electrons whereas non-metals receive electrons.

v. For example: (for positive electric charge)

Lithium(Li) has 3 protons.

The electronic configuration of sodium is 2,1.

This means that lithium has 1 electron in outermost orbit which is incomplete. During a chemical reaction, lithium (a metal) gives away the outermost electron.

Now, the no. of protons (3) in the nucleus is greater than the remaining no. of electrons (2). Hence, Li atom will get positive electric charge.

Li → Li⁺ + e^-

For example: (for negative electric charge)

Oxygen(O) has 16 protons.

The electronic configuration of sodium is 2,8,6.

This means that oxygen has 6 electrons in the outermost orbit which is incomplete. During a chemical reaction, oxygen (a non- metal) receives two electrons.

Now, the no. of protons (16) in the nucleus is less than the no. of electrons (18). Hence, oxygen atom will get negative electric charge.

O + 2e^- → O²