4.12 Homework Problem

(Polar molecules, Non-polar molecules, etc.)

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Madelyn Cearlock
Posts: 72
Joined: Fri Sep 28, 2018 12:19 am

4.12 Homework Problem

Postby Madelyn Cearlock » Sun Nov 11, 2018 11:42 am

Can someone please explain to me how they got the Lewis Structure for PF4-, and the VSEPR formula for that species, and how to predict the shape based off of that?

Joaquin Andrade
Posts: 31
Joined: Fri Sep 28, 2018 12:27 am

Re: 4.12 Homework Problem

Postby Joaquin Andrade » Sun Nov 11, 2018 12:47 pm

To draw the lewis structure, we first add up the total valence electrons. Phosphorus has 5 valence electrons, and there are 7 for each fluoride, so the total is 33. However, there is a negative 1 charge so we add one more for a total of 34. Phosphorus has the lower ionization energy so it is the central atom. We draw single bonds between it and each fluoride. Then we complete the octets for each fluoride - so far we’ve used up 32 electrons. The last two electrons are put around the phosphorus as a lone pair, since phosphorus can have an expanded octet. We should also check the formal charges - each fluoride will have a 0 formal charge, while the phosphorus will have a -1 formla charge. This makes sense because the overall charge will be -1, and we draw brackets to show this. The formula will be AX4E since there are four bonding pairs and one lone pair. From this information we also know that the shape is seesaw.

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