Chemical Bonding and Molecular Structure: VSEPR Theory – Important Questions & Preparation Tips

The chapter Chemical Bonding plays an important role in IIT JEE, UPSEE, WBJEE and various other engineering entrance examinations. This article talks about Valence Shell Electron Pair Repulsion (VSEPR) theory in detail. It also talks about different molecular shape. About 1-3 questions are being asked from this topic. The concept given in this article is in concise form and can be used for revision before the examination.

Some questions are also given in the article which have been asked in the IIT JEE previous year exams

VALENCE SHELL ELECTRON PAIR REPULSION (VSEPR) THEORY

Main Postulates of VSEPR Theory:

• The shape of a molecule depends upon the number of valence shell electron pairs (bonded or non-bonded) around the central atom.
• Pairs of electrons in the valence shell repel one another since their electron clouds are negatively charged.
• These pairs of electrons tend to occupy such positions in space that minimise repulsion and thus maximise distance between them.
• The valence shell is taken as a sphere with the electron pairs localising on the spherical surface at maximum distance from one another.
• A multiple bond is treated as if it is a single electron pair and the two or three electr on pairs of a multiple bond are treated as a single super pair.
• Where two or more resonance structures can represent a molecule, the VSEPR model is applicable to any such structure.

Shape of molecules in which the central atom has no lone pair of electrons is given in the table below

UPSEE Solved Question Paper: 2015

Shapes of some simple molecules/ions with central ions having one or more lone pairs of electrons is given below in the table

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