The steric number is calculated by summing the number of atoms bonded to a central atom and the number of lone pairs of electrons on that atom. In ethene (C2H4), each carbon atom is bonded to two hydrogen atoms and is also involved in a double bond with the other carbon atom.
For each carbon atom in ethene:
- Number of atoms bonded to carbon: 3 (2 H + 1 C)
- Number of lone pairs on carbon: 0
Therefore, the steric number for each carbon atom is:
Steric Number = Number of bonded atoms + Number of lone pairs = 3 + 0 = 3
Thus, the steric number for each carbon atom in ethene is 3.