- An ion is formed when an atom looses electron from its outer shell or gains electrons in its outer shell.
- Ions are not electrically neutral because the number of electrons and number of protons are not same.
- An ion of an element can be either positive or negative. Positive Ions are called cations and negative Ions are called anions. For example ion of Oxygen is O-2 and ion of Sodium is Na+.
- The ionic radius of a cation is always less than the atomic radius of that parent atom. For example ionic radius of Na+ is 1.02 Angstrom and atomic radius of Na is 1.57 Angstrom.
- The ionic radius of an anion is always greater than the atomic radius of the parent atom. For example ionic radius of O-2 is 1.40 Angstrom and atomic radius of O is 0.73 Angstrom.
- An atom is the smallest particle which can take part in chemical reactions and can’t be free state.
- Atoms are electrically neutral because the number of electrons and the number of protons present in nucleus are same.
- All Atoms of an element are alike.
- An atom has more number of electron compared to its cation. And it has less number of electrons compared to its anion. For example Li atom has 3 electrons while Li+ ion has only 2 electrons. Similarly F atom has 9 electrons while F– ion has 10 electrons.