Question

The partial Lewis structure that follows is for a hydrocarbon molecule. In the full Lewis structure, each carbon atom satisfies the octet rule, and there are no unshared electron pairs in the molecule. The carbon-carbon bonds are labeled 1, 2, and 3.
C ＝C － C ＝－C
Rank the carbon-carbon bonds in order of decreasing bond length.

Answer 1

Answer:

$C-C> C=C> C\equiv C$

So, 2 $>$ 1 $>$ 3

Explanation:

Carbon is a  non-metal and has 6 electrons. In the excited state, it contains 4 electrons in its outermost shell and so 4 electrons take place in covalent bond formation. In a molecule , 2 carbon atoms can be bound by a single bond, the double bond and by a triple bond. Since the bond length of $C\equiv C$ is 120 pm, the bond length of $C=C$ is 134 pm and the bond length of $C-C$ is 154 pm. Thus in the given compound, $C= C-C\equiv C$ , in which $C= C$ is labeled as 1,  $C-C$ is labeled as 2 and $C\equiv C$ is labeled as 3. So the bond length of carbon-carbon bonds in the molecule, in decreasing order is $2 > 1 >3$.