1. Notice the numbers on the diagram.
How many bonds form between two O atoms in O2? What about N2?

2. Sigma-bonding and Pi-bonding
Understanding single, double, and triple bonds

3. Sigma (σ) bonding
Valence bond theory describes covalent bonds as the result of the overlap of half-filled orbitals. A sigma bond is any covalent bond between two atoms that involves a direct, head-on overlap of orbitals.

4. Sigma (σ) bonding
All covalent bonds involving s orbitals (basically bonds involving H atoms!) are sigma bonds.
All covalent bonds involving hybrid orbitals are sigma bonds.
p-orbitals can form sigma bonds, but not all bonds involving p-orbitals are sigma.
THE FIRST BOND BETWEEN TWO ATOMS IS ALWAYS A SIGMA BOND!

7. Pi (π) bonding
A pi bond is any covalent bond between two atoms that involves the sideways overlap of parallel orbitals.
Pi bonds may involve p-orbitals or d-orbitals, but for our course, we will focus on the p-orbitals.

8. Pi bonding
Unhybridized p-orbitals will arrange themselves perpendicular to the plane where sigma bonds are occurring.
Remember from math class – two lines perpendicular to the same plane are parallel!

10. Pi bonding
THE SECOND AND THIRD BONDS BETWEEN TWO ATOMS ARE ALWAYS PI BONDS!
A double covalent bond (two lines in a Lewis structure) consists of one sigma bond and one pi bond.
A triple covalent bond consists of one sigma bond and two pi bonds.