#chemistry #textbook #ions #formationofions

Pg:- 57,58

Ch:- 4

The formation of ions occurs when atoms gain or lose electrons to achieve a more stable electronic configuration, typically resembling the electron structure of the nearest noble gas. This process is driven by the tendency of atoms to achieve a full outer electron shell (usually eight electrons, known as the octet rule).

Cation Formation (Positive Ion)

• Loss of Electrons: When an atom loses one or more electrons, it becomes a positively charged ion called a cation. This happens because the atom has more protons (positive charge) than electrons (negative charge), leading to a net positive charge.

• Example: Sodium (Na), which has 11 electrons, loses one electron to achieve a stable electron configuration like neon (Ne). This forms a sodium ion (Na⁺):

  Na→Na+ +e−

• Common in Metals: Metals, especially those in Groups 1 and 2 of the periodic table, tend to lose electrons easily, forming cations. For example, magnesium (Mg) loses two electrons to form Mg²⁺.

Anion Formation (Negative Ion)

• Gain of Electrons: When an atom gains one or more electrons, it becomes a negatively charged ion called an anion. This happens because the atom now has more electrons (negative charge) than protons, leading to a net negative charge.

• Example: Chlorine (Cl), which has 17 electrons, gains one electron to achieve the stable electron configuration of argon (Ar). This forms a chloride ion (Cl⁻):

  Cl+e−→Cl−

• Common in Nonmetals: Nonmetals, especially those in Groups 16 and 17, tend to gain electrons and form anions. Oxygen (O) gains two electrons to form O²⁻.

Key Points

• Ionic Bonding: Once ions form, they can attract oppositely charged ions through electrostatic forces, leading to the formation of ionic bonds. For example, Na⁺ and Cl⁻ form sodium chloride (NaCl), a common salt.

• Stability: Atoms form ions to achieve greater stability, which usually means achieving a full outer shell of electrons, similar to the electron configuration of the nearest noble gas.