Final answer:
Carbon atoms involved in a triple bond use sp hybridization, with terminal carbon atoms forming two pi bonds and one sigma bond. Carbon atoms with four single bonds exhibit sp³ hybridization, forming only sigma bonds with tetrahedral geometry.
Step-by-step explanation:
In molecular geometry and hybridization of carbon atoms, different types of hybrid orbitals are used depending on the number and types of bonds that a carbon atom forms. In a molecule where a carbon atom forms a triple bond, the hybridization of the terminal carbon atoms is sp hybridized, indicating that this atom has two regions of electron density—a sigma (σ) bond and two pi (π) bonds.
The sp hybrid orbitals consist of one s and one p orbital combining, which results in two sp orbitals that form the σ bond part of the triple bond. The remaining two p orbitals on each carbon form the two π bonds of the triple bond. Conversely, in carbon atoms bonded to four other atoms (exhibiting four regions of electron density), sp³ hybridization occurs where one s and three p orbitals mix to form four sp³ hybrid orbitals—these are used to form sigma bonds in tetrahedral geometry.