Sixth Edition. Question 4.109

[Dayna Pham 1I]

Question 4.109 is:
4.109 Estimate the bond angles marked with arcs and lowercase letters in peroxyacetylnitrate, an eye irritant in smog.

It adds an image of the molecule, which is attached.

But why is angle b around 109.5 degrees? It only has two regions of electron density, so I expected it to be linear, with a bond angle of 180 degrees. Is this because it has lone pairs that are not shown in the image, which turns it into tetrahedral arrangement, but bent shape?

Thanks!

[Sarah Fatkin 4I]

Hi Danya! You're right, it's because oxygen has two lone pairs, which means that the structure has tetrahedral shape and bond angles of 109.5 degrees.

[Ava Kjos 1D]

That is correct, since there are only two single bonds with oxygen you can assume that there are two lone pairs that are not shown to finish the octet around oxygen. Therefore, the shape must be bent with an angle of 109 degrees.

[Ian Marquez 2K]

To reiterate, here there are 4 areas of electron density around the oxygen. The two lone pairs are not shown but have to be present to complete the octet. It is a tetrahedral configuration with the VSEPR equation of AX2E2, meaning that it is of bent shape with about a 109.5 degree angle.

[Katelyn Phan 2A]

Great question! Though not drawn, it is assumed that there are two lone pairs attached to oxygen to complete the octet. Therefore there's a total of 4 regions of electron density. The lone pairs repel each other and the bonded pairs thus creating a bent shape. This has the bond angle of 109.5.