An orbital view of covalent bonding

Valence bond theory states that

if two atoms have orbitals which contain unpaired electrons then the orbitals will overlap, forming a covalent bond.

How many sigma and pi bonds does this molecule contain?

9 sigma bonds and 3 pi bonds

When orbitals overlap end-on they form a

sigma bond

When orbitals overlap side-on they form a

pi bond

How many sigma and pi bonds does a double bond contain?

1 sigma and 1 pi

How many sigma and pi bonds does a triple bond contain?

1 sigma and 2 pi

How many sigma and pi bonds does a single bond contain?

1 sigma and 0 pi

classifying sigma and pi bonds is based on rotation:

In a sigma bond, one of the atoms can rotate around the bond axis without affecting the amount of overlap between the two orbitals

In a pi bond, if one of the atoms rotates around the bond axis, the amount of overlap would change 

How can Xenon can make 4 bonds in XeF₄?

because it can promote 2 electron(s) from a/the 5p orbital(s) to a/the 5d orbital(s)

Sulfur can make 6 bonds in SO₃​ because…

it can promote 1 electron(s) from a/the 3s and 1 electron(s) from a/the 3p orbital(s) to a/the 3d orbital(s)

In Period 3: phosphorus, sulfur and chlorine can all form extra bonds by promoting electrons into their 3d orbitals.

In Period 2: nitrogen, oxygen and fluorine cannot form extra bonds by promoting electrons.

Suggest why.

there are no orbitals close enough in energy to the 2⁢p orbitals

2⁢d orbitals don’t exist