In the molecule $C_2{H}_4$ (ethene), how many $s–{\mathrm{sp}}^2$ sigma bonds are present?

• A. $2$
• B. $1$
• C. $5$
• D. $4$

Answer: (D)

Verified step by step guidance

1. Identify the molecular structure of ethene (C\_2H\_4). Ethene consists of two carbon atoms double bonded to each other, and each carbon is bonded to two hydrogen atoms.
2. Recall that in ethene, each carbon atom is \( sp^2 \) hybridized. This means each carbon forms three sigma (\( \sigma \)) bonds using its three \( sp^2 \) hybrid orbitals, and one pi (\( \pi \)) bond using the unhybridized p orbital.
3. Count the sigma bonds between the atoms: each carbon forms two sigma bonds with hydrogen atoms, so for two carbons, that accounts for \( 2 \times 2 = 4 \) C-H sigma bonds.
4. There is also one sigma bond between the two carbon atoms (the sigma component of the double bond).
5. Add the sigma bonds together: \( 4 \) C-H sigma bonds plus \( 1 \) C-C sigma bond equals \( 5 \) sigma bonds in total. However, since the question asks specifically for the number of \( sp^2 \) sigma bonds, consider only those formed by the \( sp^2 \) orbitals, which are the same five sigma bonds counted here.