Step-by-step explanation:
According to orbital hybridization theory, in ethene the C atoms are using sp2 hybrid orbitals. This leaves one unhybridized p orbital available to form the second bond (Pi bond) in the C-C double bonds.
One sp2 hybrid orbital from each C atom overlap to form one sigma bond between the two carbon atoms. One p orbital from each C atom then overlap to form a pi bond that completes the C-C double bond. The H atoms are bonded via sigma bonds to the C atoms when the H s orbitals overlap with the remaining sp2 hybrid orbitals from each C.