In the molecule ethene (C2H4), how many sigma bonds are present?

• A. 6
• B. 4
• C. 3
• D. 5

Answer: (A)

Verified step by step guidance

1. Recall that a sigma (\sigma) bond is the first bond formed between two atoms and is characterized by head-on overlap of orbitals.
2. Identify the types of bonds in ethene (C2H4): it has a double bond between the two carbon atoms and single bonds between each carbon and its attached hydrogens.
3. Understand that a double bond consists of one sigma bond and one pi bond, so the C=C double bond contributes one sigma bond.
4. Count the sigma bonds between carbon and hydrogen atoms: each carbon is bonded to two hydrogens, so there are 4 C-H sigma bonds in total.
5. Add the sigma bonds: 1 (from the C=C bond) + 4 (from the C-H bonds) = total number of sigma bonds in ethene.