Question

select the correct answer. which structure correctly represents the bonding in a hydrocarbon molecule?
a. structural formula with carbon and hydrogen atoms

b. structural formula with carbon and hydrogen atoms, including a triple bond

c. structural formula with carbon and hydrogen atoms

d. structural formula with carbon and hydrogen atoms, including a double bond

Explanation:

Hydrocarbons are compounds composed only of carbon (C) and hydrogen (H) atoms. Let's analyze each option:

• Option A: The structure has a carbon atom with 5 bonds (a C atom is bonded to 5 other atoms, but C can form at most 4 bonds), which is invalid (violates the octet rule for C).
• Option B: All atoms are C and H. The triple bond between two C atoms is valid (C can form triple bonds, and each C still has a total of 4 bonds when considering single bonds with adjacent C and H atoms), and the structure follows the bonding rules for hydrocarbons.
• Option C: There is a carbon atom with 5 bonds (a central C bonded to 5 other atoms), which is invalid (C can only form 4 bonds).
• Option D: The structure has a carbon atom with 5 bonds (the C in the double bond has an extra bond), violating the octet rule for C.

So only Option B has a valid structure for a hydrocarbon.

Answer:

B. $\ce{H - \overset{H}{\underset{H}{C}} - \overset{H}{\underset{H}{C}} - \overset{H}{\underset{H}{C}} - \overset{H}{\underset{H}{C}} - \overset{H}{\underset{H}{C}} \equiv \overset{H}{\underset{H}{C}} - \overset{H}{\underset{H}{C}} - \overset{H}{\underset{H}{C}} - H}$ (the structure in Option B)