2.2B VSEPR Theory

Covalent Bonds

Every covalent bond is characterized by two values:

Bond length: the distance between bonded nuclei

Bond strength: the amount of energy needed to break the bond. It is also called bond enthalpy.

In general...

Shorter bonds are stronger bonds

Multiple Bonds

Atoms can share more than one pair of electrons to form multiple bonds.

A double bond forms when two pairs of electrons (4e^- in total) are shared

A triple bond forms when three pairs of electrons (6e^- in total) are shared

Multiple bonds have a greater number of shared electrons and so have a greater force of electrostatic attraction between the bonded nuclei.

Bond Length

Shortest: Triple Bonds < Double Bonds < Single Bonds :Longest

Bond Enthalpy

Lowest: Single Bonds < Double Bonds < Triple Bond :Highest

Molecular Shapes: Valence Shell Electron Pair Repulsion Theory (VSEPR) Theory

electrons in covalent bonds and in lone pairs repel one another

Molecules have 3D shapes that place electron pairs on the central atom as far apart as possible.

Shapes of molecules are determined by...

1. The number of atoms bound to the central atom

2. The number oflone pairs of electrons on the central atom

Electron domains can be single, double, or triple bonding electron pairs or non-bonding pairs of electrons

Total number of electron domains determine the geometric arrangements of electron domains

Lone pairs of electrons have a higher concentration of charge and so cause slightly more repulsion than bonding pairs