# Bond lengths

Gold Member

## Homework Statement

In which of the following pairs of bonds is the shorter bond length not followed by the longer
bond length?

(1) S―O, P―O
(2) C≡C, C=C
(3) C=O, C=S
(4) C―Si, C―S
(5) N≡O, N=O

## Homework Equations

Bond length is determined by the bond order (number of bonds) and bond length is also an indicator of bond strength. The stronger the bond, the shorter the bond. The more bonds, the shorter the bonds.

## The Attempt at a Solution

Choices 2 and 5 can be immediately eliminated since the triple bonds are obviously shorter than the double bonds.

I'm having a hard time narrowing down between the remaining choices (1, 2, and 4). How do I go about determining which bonds are shorter or longer? Does it depend on electronegativity? Strength?

## Answers and Replies

mfb
Mentor
The size of the atoms (more precise: the outer electrons) is important, too. If you look downwards within a chemical group, atom diameters increase as more and more shells get filled.

Gold Member
Well sulfur is a smaller atom than silicon according to periodic trends so 4 must be the answer.

dextercioby