Question

1) how does the presence of lone pairs affect the angle between the atoms bonded to central atom?

2) draw the more stable valence electron orbital diagram for carbon.

3) if a carbon bond is sp3 hybridizedit must have ___ sigma bonds and ___ pi bond. The shape of the molecule at the pi bond must be _______.

Answer 1

Answer 1)   The presence of the lone pairs, which occupy more space than the bonding pairs, affects the repulsive forces between the valence electrons in molecules. The electrons in a lone pair are attracted to only one atom, as they are unshared, and so are considered to be closer to the nucleus than the electrons in a bonding pair which are shared between two atoms. The degree of the repulsion between electron pairs, therefore lies in the order:

Lone Pair - Lone Pair > Lone Pair - Bond Pair > Bond Pair - Bond Pair

This means that the presence of lone pairs will change the shape of a molecule.

Bond angle is affected by the presence of lone pair of electrons at the central atom. A lone pair of electrons at the central atom always tries to repel the shared pair (bonded pair) of electrons. Due to this, the bonds are displaced slightly inside resulting in a decrease of bond angle.

Answer 2) Carbon has 6 electrons, two in 1s orbital, and four valence electrons that occupy the 2s and 2p valence orbitals.

Answer 3) If a carbon bond is sp3 hybridized it must have 4 sigma bonds and zero pi bond. Since , all the three 2p orbitals are involved in sigma bonding and there is no 2p orbital left for pi bonding. The shape of the molecule must be tetrahedral.

Example: CH4