# POI is a bent molecule similar to water. How are the two molecules different it terms of bond angles and what causes this?

phosphorus oxyiodide ($$\ce{POI}$$) has the VSPER AXE formula of $$\ce{AX2E}$$ while water, $$\ce{H2O}$$ has the AXE code of $$\ce{AX2E2}$$. According to my work sheet $$\ce{POI}$$ should have a $$120^\circ$$ bond angle while $$\ce{H2O}$$ should have a bond angle of $$104.5^\circ$$.

Does this mean that due to the extra lone pair it creates less resistance resulting in a greater angle? Also, does it having three different elements in the equation do anything?

• You mean the molecule O=P–I? Because to me, italicised $POI$ sounds like... a triangle, in geometry. – orthocresol Oct 9 '18 at 23:19
• The worksheet says $POI$ multiple times. In those exact words. I can't seem to find it on the internet. Either there is a mistake (which was repeated multiple times) or it is made up to prove a point? – Zebert Oct 9 '18 at 23:26
• Well, I'm pretty sure the molecule doesn't exist. But it does fit into the VSEPR scheme of $\mathrm{AX_2E}$, which is why I suspected it was that. And if your only goal is to learn how to apply VSEPR theory, it doesn't particularly matter whether the compound exists or not; you just need to be aware of what you are saying, i.e. "if this molecule existed, VSEPR would predict a bond angle of x degrees" and not "this molecule has a bond angle of x degrees". – orthocresol Oct 9 '18 at 23:28

Does this mean that:

Due to the extra lone pair $$\color{red}{\text{it}}$$ $$\color{limegreen}{\text{creates less resistance}}$$ resulting in $$\color{blue}{\text{a greater angle}}$$?

More like:

Due to the extra lone pair $$\color{red}{\text{in } \ce{H2O} \text{ the pendant atoms}}$$ $$\color{limegreen}{\text{experience more repulsion}}$$ resulting in $$\color{blue}{\text{a smaller angle}}$$ $$\color{magenta}{\text{compared to }\ce{POI}}$$?

Also, does it having three different elements in the equation do anything?

No, I think the three different elements in the question were there to evaluate if you were:

1. estute to the fact that oxygen forms a double bond thus
2. phosphorous has 1 unbonded pair of electrons (not 2) and
3. if the double bond would hang you up in obtaining an answer.