In the molecule, C2H4, what are the atomic

orbitals that participate in forming the sigma

bond between the C and H atoms

Ethene (C2H4) is an alkene which means this compound has a double bond between the carbons. The hybridization hence is sp2. In this hybridization, the 2s orbital mixes with only two of the three available 2p orbitals, forming a total of 3 sp2 orbitals with one p-orbital remaining.