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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?

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  • $\begingroup$ You mean the molecule O=P–I? Because to me, italicised $POI$ sounds like... a triangle, in geometry. $\endgroup$ – orthocresol Oct 9 '18 at 23:19
  • $\begingroup$ 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? $\endgroup$ – Zebert Oct 9 '18 at 23:26
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    $\begingroup$ 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". $\endgroup$ – orthocresol Oct 9 '18 at 23:28
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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.
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