Exam
Chemistry
Number of molecules having bond order 2 from the following molecules is _________.
C2,O2,Be2,Li2,Ne2, N2,He2
Correct Answer:
2
Explanation
To determine the number of molecules with a bond order of 2 from the given molecules, we need to first calculate the bond order for each molecule. The bond order can be determined using Molecular Orbital Theory (MOT). The bond order is given by the formula:
Bond Order=2Number of bonding electrons−Number of anti-bonding electrons
Let's evaluate each molecule individually:
1. C2:
For
C2
, the total number of electrons is 12. The molecular orbital configuration will be (σ1s)2(σ1s∗)2(σ2s)2(σ2s∗)2(π2px)2(π2py)2
. There are 8 bonding electrons and 4 anti-bonding electrons:
Bond Order=28−4=2
2. O2:
For
O2
, the total number of electrons is 16. The molecular orbital configuration will be (σ1s)2(σ1s∗)2(σ2s)2(σ2s∗)2(σ2pz)2(π2px)2(π2py)2(π2px∗)1(π2py∗)1
. There are 10 bonding electrons and 6 anti-bonding electrons:
Bond Order=210−6=2
3. Be2:
For
Be2
, the total number of electrons is 8. The molecular orbital configuration will be (σ1s)2(σ1s∗)2(σ2s)2(σ2s∗)2
. There are 4 bonding electrons and 4 anti-bonding electrons:
Bond Order=24−4=0
4. Li2:
For
Li2
, the total number of electrons is 6. The molecular orbital configuration will be (σ1s)2(σ1s∗)2(σ2s)2
. There are 4 bonding electrons and 2 anti-bonding electrons:
Bond Order=24−2=1
5. Ne2:
For
Ne2
, the total number of electrons is 20. The molecular orbital configuration will be (σ1s)2(σ1s∗)2(σ2s)2(σ2s∗)2(σ2pz)2(π2px)2(π2py)2(π2px∗)2(π2py∗)2(σ2pz∗)2
. There are 10 bonding electrons and 10 anti-bonding electrons:
Bond Order=210−10=0
6. N2:
For
N2
, the total number of electrons is 14. The molecular orbital configuration will be (σ1s)2(σ1s∗)2(σ2s)2(σ2s∗)2(σ2pz)2(π2px)2(π2py)2
. There are 10 bonding electrons and 4 anti-bonding electrons:
Bond Order=210−4=3
7. He2:
For
He2
, the total number of electrons is 4. The molecular orbital configuration will be (σ1s)2(σ1s∗)2
. There are 2 bonding electrons and 2 anti-bonding electrons:
Bond Order=22−2=0
Thus, the molecules with a bond order of 2 from the given list are
C2
and O2
. Therefore, the number of molecules having bond order 2 is 2.Select an option to instantly check whether it is correct or wrong.
