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Posted: Tue Dec 05, 2017 1:39 pm
When drawing the product of the reaction between PF5 and F-, how do you know that the resulting compound, PF6, has a negative charge?
Posted: Tue Dec 05, 2017 2:03 pm
Well PF5 has a neutral charge and by adding the F- ion, it results in the overall compound having a negative charge.
Posted: Tue Dec 05, 2017 2:25 pm
You can also count the number of electrons each compound or ion has. PF5 would have 40 electrons and F- would have 8 electrons. If PF6 didn't have a charge it would only have 47 electrons, but the structure should have the same number of electrons as its reactants, so it would need an extra electron, and therefore have a negative charge.
Posted: Thu Dec 07, 2017 4:24 pm
Look at formal charges, you know that phosphorus likes to make 5 bonds since it has a valence number of 5, however in the case of PF6 it is making 6 bonds, resulting in a -1 charge.