Molecular Geometry

Basic Terminology Molecule

Group of atoms held together by covalent bondsBond Length

Distance between 2 bonded atoms Bond Energy

Energy required/needed to break a chemical bond Bond Angles

Determined based on bonding and nonbonding regions of the central atom in a molecule

Why is molecular shape/structure SO

important?

Molecular Shape 3-D structure of a molecule

Predicted from the Lewis dot diagram of a chemical compound

“VSEPR” Theory/Electron Domain (ED) Model

Valence electrons repel each other Electrons are arranged so the distance between

them is MAXIMIZED !Electron pair orientations influence the

shape/structure of a molecule Focus on central atom

Shared electronsUnshared electrons

Ex. BeF2

What about unshared electrons on the central

atom?Lone/unshared electrons

Occupy space around central atom Not involved in chemical bonding between atoms

These pairs are NOT taken into account for a chemical molecule’s shape ! Require MORE space than shared electrons,

indirect contribution to shape

Molecular Shapes 1) Bent2) Trigonal Pyramidal3) Tetrahedral4) Trigonal Planar 5) Two atom Linear6) Linear

1) Bent

Ex. H2O

2) Trigonal Pyramidal

Ex. NH3

3) Tetrahedral

Ex. CH4

4) Trigonal Planar

Ex. BF3

5) Two atom Linear

Ex. I2

6) Linear

Ex. CaCl2