Chemical Bonding and Molecular Structure — Part 2: Shapes, hybridisation, MO theory and hydrogen bonding: visual lesson, CBSE Class 11 Chemistry

Lesson

Shapes of molecules and theories of bonding

Part 2 — three models of molecules: VSEPR for shape, valence bond theory with hybridisation for bonding, and molecular orbital theory for magnetism and bond order.

In this lesson you will

Predict shapes of AB₂ to AB₆ molecules with and without lone pairs using VSEPR theory
Explain valence bond theory, σ and π bonds, and sp, sp², sp³, sp³d and sp³d² hybridisation
Build MO diagrams for H₂ to Ne₂ and deduce bond order and magnetic behaviour
Describe intermolecular and intramolecular hydrogen bonding and its effects

Table linking the number of electron pairs to the arrangement and hybridisation
Electron pairs	Arrangement	Hybridisation
2	Linear	sp
3	Trigonal planar	sp²
4	Tetrahedral	sp³
5	Trigonal bipyramidal	sp³d
6	Octahedral	sp³d²

Concept

VSEPR theory

Electron pairs around the central atom repel and take positions of minimum repulsion. Order of repulsion: lone pair–lone pair > lone pair–bond pair > bond pair–bond pair. A multiple bond counts as one region of electron density. The shape names only the atoms.

Table of the three kinds of electron-pair repulsion in decreasing order of strength
Repulsion	Strength	Effect on angles
Lone pair–lone pair	Greatest	Squeezes the other angles
Lone pair–bond pair	Intermediate	Reduces bond angles
Bond pair–bond pair	Smallest	Gives the ideal angle

Diagram

Shapes with no lone pairs: AB₂ to AB₆

Schematic; solid lines are in or near the plane of the page, dashed lines point backwards.

With no lone pairs the shape matches the arrangement: linear (BeCl₂), trigonal planar (BF₃), tetrahedral (CH₄), trigonal bipyramidal (PCl₅; axial bonds are longer than equatorial) and octahedral (SF₆).

Cookies