shortcut

Well for our syllabus, apart from NO^- and O₂, all molecules with integral bond orders are diamagnetic (the exceptions I mentioned are paramagnetic due to Hund's rule which causes singlet occupation in 2p orbitals). The ones having fractional bond order are paramagnetic. This is a rough rule which works within the scope of our syllabus.

To find bond order, there is a nice quickie method my friend told me. Msg me in my chatbox and I'll tell you.

i found out this on one of the discussions here on tiit.

pritish is this the shortcut you were talking abt or something else?

Well since it's being demanded so much....here it is. It requires a little knowledge of the periodic table.

Steps to find the bond order -:
1. If the element is in a group number less than 8, then subtract 8 from its group number. For eg, nitrogen = 7, oxygen = 8, fluorine = 9, etc.

2. Add up such numbers from each of the constituent atoms. For eg, for N₂, 7 + 7 = 14.

3. Subtract 8 again.

4. After this subtraction, with the number you have left, you put 6(REQUIRED at all costs...if you have a number smaller than 6 after subtraction, put all you have) into the bonding orbital. After putting minimum 6 into bonding orbital, put the rest into antibonding orbital.

5. Now you can easily find bond order.

Let's do this by example. How about N₂?
1. 15 - 8 = 7.

2. For two N atoms, 7 + 7 = 14.

3. 14 - 8 = 6.

4. N_B = 6, N_A = 0 [These are not the actual figures of electrons in those orbitals. Just for the formula]

5. BO = 1/2(6 - 0) = 3 which is indeed so! N₂'s triple bond shows here.