# What is bond order? How we can determine it? Please basics. Thank you so much.

##### 1 Answer

*A conceptual approach is to simply count electrons in a bond and treat each bonding valence electron as half a bond order.*

This works for many cases, except for when the highest-energy electron is in an antibonding molecular orbital.

**SIMPLE CASE**

For example, the **bond order** of *bonding* valence electron contributes half a bond order.

So:

#"BO"_"triple" = "BO"_sigma + 2"BO"_pi = 1/2 xx ("2 electrons") + 2(1/2 xx ("2 electrons")) = 3# for the bond order, as we should expect, since bond order tells you the "degree" of bonding.

**MULTI-ATOM CASE**

Or, in a more complicated example, like

So, in

That means its **bond order** is simply

#"BO" = "BO"_sigma + "BO"_pi = 1 + 0.333 = 1.333# .

Therefore, **three** "**bonds** overall (instead of one double bond and two single bonds), meaning it is one third of the way between a single bond and a double bond.

**EXCEPTION EXAMPLE: O2**

If we were to calculate its bond order, we would get

But what if we wanted the bond order for *What is it actually?*

You may realize that we would have removed one electron from an ** antibonding** molecular orbital. That means we've removed half a bond order corresponding to

**, which is the same as adding half a bond order corresponding to**

*antibonding character***.**

*bonding character*So, by *removing* an *antibonding* electron, we've done the equivalent of *adding* a *bonding* electron.

**In other words, we've decreased a bond-weakening factor, thereby increasing the bonding ability of the molecule.**

Therefore, the actual bond order of