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Question

How would the bond length vary in dicarbon speciesC2,C2+,C2-


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Solution

Bond length and Bond order:

  • The distance between the centres of two covalently bound atoms is denoted as bond length.
  • The number of bound electrons determines the length of the bond which is called the bond order.
  • The stronger the attraction between the two atoms and the shorter the bond length, the higher the bond order.
  • Bond order can be calculated as:

Bondorder=12(numberofelectronsinbondingorbitals-numberofelectronsinantibondingorbitals)

  • The bond order of the dicarbon species C2,C2+,C2- can be calculated using the same formula.
    • Energy level diagram of C2 molecule:
  • According to molecular orbital theory, C2​ molecule has one σ and one Ï€ bond.
  • The M.O. electronic configuration is σ2s2σ∗2s2Ï€2px2​π2py2​
    Bondorder=12(numberofelectronsinbondingorbitals-numberofelectronsinantibondingorbitals)Bondorder=6-22=2
  • The bond order results show that the C2- has the highest number of valence electrons and the highest bond energy. Therefore, C2- supposedly has the shortest bond length.
  • C2+ has lesser bond energy than C2. Therefore, C2+ has a longer bond length than C2.

So, the order starting with the highest bond length is C2-<C2<C2+


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