Summary
Highlights
To count sigma bonds, count all single bonds and then add one for each multiple bond. To count pi bonds, count one for each double bond and two for each triple bond. An example structure is analyzed showing seven sigma bonds and two pi bonds.
Hybridization is the process of combining atomic orbitals to form hybrid orbitals. Examples include sp3 (one s orbital and three p orbitals), sp2 (one s and two p orbitals), sp (one s and one p orbital), and d2sp3 (two d, one s, and three p orbitals).
An s orbital is spherical, representing the most probable location of an electron. There are three types of p orbitals (px, py, pz), oriented along the x, y, and z axes respectively. Electrons behave as both particles and waves, and their exact location cannot be precisely known due to Heisenberg's uncertainty principle.
Carbon's electron configuration is 1s2 2s2 2p2. In sp3 hybridization, carbon uses all four valence orbitals (one s and three p orbitals). The resulting sp3 hybrid orbitals have 25% s character and 75% p character, placing their energy level closer to the 2p orbital than the 2s. All four sp3 hybrid orbitals are degenerate, meaning they have the same energy, and electrons are added one at a time with parallel spins.
For sp2 hybridization, one s orbital and two p orbitals are combined, leaving one p orbital unhybridized. The sp2 hybrid orbitals have approximately 33% s character and 67% p character, positioning their energy level closer to 2p but lower than sp3. Three degenerate sp2 hybrid orbitals are formed, along with one unhybridized 2p orbital.
In sp hybridization, one s orbital and one p orbital are mixed, leaving two p orbitals unhybridized. The sp hybrid orbitals have 50% s character and 50% p character, placing their energy level exactly between the s and p orbitals. Two degenerate sp hybrid orbitals are formed.
Hybrid orbitals form sigma bonds, while unhybridized p orbitals form pi bonds. Every single bond contains one sigma bond. Double bonds consist of one sigma bond and one pi bond. Triple bonds contain one sigma bond and two pi bonds. Triple bonds are stronger and shorter than single bonds. Sigma bonds are generally stronger than pi bonds, even though triple bonds (with two pi bonds) are stronger than single bonds (one sigma bond) due to the presence of multiple bonds.