Final answer:
An sp2 hybridized central carbon atom participates in sigma bonding through three sp2 hybrid orbitals in a trigonal planar arrangement and one pi bonding through an unhybridized p orbital, as seen in molecules like formaldehyde and ethene.
Step-by-step explanation:
An sp2 hybridized central carbon atom with no lone pairs of electrons engages predominantly in sigma (σ) bonding and one π (pi) bonding. This occurs because sp2 hybridization involves the use of three sp2 hybrid orbitals and one unhybridized p orbital. The three sp2 hybrid orbitals form sigma bonds, orienting in a trigonal planar geometry to minimize electron repulsion. These can be single bonds to other atoms or part of a double bond in which one of the bonds is a sigma bond. The unhybridized p orbital is used to form the pi bond, which is a part of the double bond along with one of the sigma bonds.
Examples of molecules with an sp2 hybridized central carbon atom include formaldehyde (CH₂O), where the carbon has two single bonds with hydrogen and one double bond with oxygen, and ethene (H₂CCH2), which has two carbon atoms double-bonded to each other, each carrying two single bonds to hydrogen atoms.