What is Hypovalent species or compounds ?

The compounds or ions which doesn't follow octet rule inspite of that contains less than eight electrons and also stable called Hypovalent species.

For examples BeF₂,BF₃, CH₄⁺, NF₂⁺, B₂H₆, Be₂Cl₄ etc

Hypovalent species may act as Lewis acid always.

What is Hypervalent species or compounds?

The compounds or ions which doesn't follow octet rule inspire of that contains more than eight electrons and also stable called Hypervalent species.

For examples XeFe₂(10e), XeFe₄(12e), SF₄(10e), SFe₆(12e), IFe₇(14e), I₂Cl₆(10e), TeF₅(12e) etc

Hypervalent species may act as Lewis acid but not always.

Cage like Structure

P₄, P₄O₄, P₄O₁₀, P₄S₃, P₄S₁₀, N₄(CH₂)₆

Structure of P4O6 and P4O10

Normal Oxides:

The Oxides in which oxidation state of central atom is found to be one of the it's common oxidation state. The are also called acid anhydrides because on dissolving them  into water oxygen acid is formed in which oxidation state of central atom is found to be same as present in Oxide.

Examples:  B₂O₃, CO₂, N₂O₃, N₂O₅, SO₂, SO₃, Cl₂O₇, XeO₃, XeO₄ etc.

Peroxides

The oxides in which  calculated oxidation state of central atom is more than maximum oxidation state of central atom due to the presence of peroxide linkage.

For examples, H₂O₂, Na₂O₂, BaO₂, PbO₂, CrO₅ etc.