Question
Question: Which of the following is/are true for \({{B}_{2}}\) and \({{C}_{2}}\) molecules according to M.O.T?...
Which of the following is/are true for B2 and C2 molecules according to M.O.T? (This question has multiple correct options).
(a)- Both are having 1−σ and 1−π bond
(b)- Both are having the same bond length.
(c)- Both are having different bond orders.
(d)-B2 is paramagnetic andC2 is diamagnetic.
Solution
If the compound has an unpaired electron then it is paramagnetic, and if it has all paired electrons then it is diamagnetic. We can calculate the bond order of the compound by dividing the sum of electrons in bonding orbital and antibonding orbital with 2.
Complete answer:
Let us study all the options one by one:
(a)- Both are having 1−σ and 1−π bond
B2 molecule has a single bond between both boron atoms. Hence, it has a σ bond.
In C2 molecules there are 2 bonds. One is σ bond and the other is π bond.
Hence, this option is incorrect.
(b)- Both are having the same bond length.
The bond length of the molecule is related to the bond order of the molecule. Bond length is inversely proportional to the bond order.
In B2, molecule the bond order is 1 and the bond order of C2 is 2. Hence, the bond length of C2 is shorter than B2.
Hence, this option is also incorrect.
(c)- Both are having different bond orders.
The bond order of the compound is calculated by dividing the sum of electrons in bonding orbital and antibonding orbital with 2.
B2 has 6 electrons in its outermost shell . Configuration is : σ2s2 σ∗2s2 π2px1 π2py1
Bond order = 2b.o−a.b.o=24−2=1
C2 has 8 electrons in its outermost shell . Configuration is: σ2s2 σ∗2s2 π2px2 π2py2
Bond order = 2b.o−a.b.o=26−2=2
Hence, this option is correct.
(d)- B2 is paramagnetic and C2 is diamagnetic in nature.
B2 has two unpaired electrons hence, it is paramagnetic. C2 has all paired electrons hence, it is diamagnetic.
Hence, this is also correct.
So, the correct answer is “Option C and D”.
Note: The orbital π2px and π2py gets degenerate after mixing hence they have same energy. So, if there are 2 electrons left each of them gets one-one electron each after that only pairing is done.