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Organic Chemistry

Valence Shell Electron Pair (VSEPR) theory

In his landmark paper, 'The Atom and the Molecule,' G.N. Lewis attempted to describe linkages between the atoms to understand the nature of covalent bonds.

He used dots to represent an atom’s valence electrons and argued that the atoms share their valence electrons to form one, two, or three bonds until they attain a stable octet electron configuration. An exception is the Hydrogen atom that attains a duplet configuration.  

How to determine the hybridization of C in CH4?

If only valence shells participate in bonding reactions, then Carbon should only form two bonds using its two unpaired electrons. However, Carbon forms four bonds, as seen in CH4, CH3X, H2C=O, and O=C=O molecules. This discrepancy between the number of valence electrons of an atom and the number of bonds it forms (valency) is explained by the hybridization concept, an extension of the Valence Bond (VB) Theory.