The number of sigma bonds in acetaldehyde (CH₃CHO) is x.

Solution

Chemistry ma’am · 4 steps

Every single bond is a sigma; a double bond gives one sigma plus one pi.

1. Draw the skeleton. Acetaldehyde is CH₃-CHO: a methyl carbon joined to the aldehyde carbon, which carries the C=O group and one C-H bond.
2. Count C-H bonds. The methyl group has three C-H bonds, and the aldehyde carbon has one more. That is 4 sigma bonds from C-H alone.
3. Add carbon bonds. The C-C single bond gives 1 sigma. In the C=O double bond, only one of the two bonds is sigma; the other is pi. So C=O contributes 1 sigma.

   σ = 4 + 1 + 1 = 6

4. So. The total number of sigma bonds in acetaldehyde is 6.

The common slip. Counting the C=O double bond as two sigma bonds gives 7 instead of 6.

The idea to keep. Count sigma bonds bond by bond: every single bond is one sigma, and a double bond adds one sigma plus one pi.

Answer from the NTA final answer key. Solution by PrepWiser.