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Homework Help: Bond lengths

  1. Oct 15, 2013 #1


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    1. The problem statement, all variables and given/known data

    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

    2. Relevant 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.

    3. 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?
  2. jcsd
  3. Oct 15, 2013 #2


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    Staff: 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.
  4. Oct 15, 2013 #3


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    Well sulfur is a smaller atom than silicon according to periodic trends so 4 must be the answer.
  5. Oct 15, 2013 #4


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    Homework Helper

    The bond length depends on the distance of the 2 nuclei one to another and the density of the electronic 'cloud' between them. The larger the atomic radius and the more electrons appear in a bond, the effects are just opposite.
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