1. Periodicity of Hydra Acids

(a) Acidic character of hydra acid increases from left to right in a period.

Acidic-character-of-hydra-acid-increases-from-left-to-right-in-a-period.

(b) Acidic character of hydra acid increases from top to bottom in a group.

Acidic-character-of-hydra-acid-increases-from-top-to-bottom-in-a-group

2. Periodicity of Oxy Acids

(a) Acidic character of oxy acid increases from left to right in a period.

Acidic-character-of-oxy-acid-increases-from-left-to-right-in-a-period.

(b) Acidic character of oxy acid decreases from top to bottom in a group.

Acidic-character-of-oxy-acid-decreases-from-top-to-bottom-in-a-group.

3. Acid-Base Character of Oxides

  1. On moving across a period, the basic character of oxides gradually decreases, and the acidic character increases.
  2. The stability of oxides decreases across a period.

acid-base-character-of-oxides-300x149

Note:

  • Oxides of Element M in H2O produce MOH.
  • If the electronegativity difference of M and O is greater than that of H and O in H2O then MOH is acidic due to the formation of H3O+.

formation-of-H3O-300x36

  • If the electronegativity difference of M and O in MOH is lesser than that of O and H in H2O then MOH is basic due to the formation of OH–.

formation-of-OH–

  • Oxides of the following elements are amphoteric.
    Zn, Al, Be, Ga, Pb, Sn, As, Sb, Bi, In, Ge
  • H2O is amphoteric (also called amphiprotic)

amphoteric-nature-of-water

  • BeO, Al2O3, SnO2, PbO2 …………… are amphoteric since they form salts with acid as well as with base.

amphoteric-oxides

  • Oxides are acidic if they react with base.
  • Oxides are basic if they react with acid.

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