Module 1 : Introduction
Lecture 1 : Bonding concept s in main group chemistry
 

For some molecules, Lewis dot structure differs from the experimentally determined structural observations. For example, in acetate ion both the C—O bonds are identical as per X-ray structure determination but the prediction by the Lewis structure is incorrect. The reason is due to resonance.

Limitations of Lewis model

Molecules with odd number of electrons can never satisfy the octet rule.

Example: NO.

Some atoms with fewer valence electrons can never complete octet without formal charges.

A central atom can have more than 8 electrons. Example: SF6

Lewis model does not explain paramagnetic nature of O2.

Geometry and molecular shapes cannot be explained by Lewis model.