2B.7

[Kristina Rizo 2K]

2B.7 "The following Lewis structure was drawn for a Period 3 element. Identify the element." The Lewis structure given was an Oxygen double bonded to E (the unknown element) and 3 Chlorine elements that have a single bond with E. I was wondering if I am supposed to use the formal charge to figure out what the element E is?

[MinuChoi]

You can use valence electron values to identify E.

Count how many electrons are in the Lewis structure. It looks like the structure has 32 electrons based on the four bonds described.

You also know the structure has an atom of element E, one oxygen, and three chlorines. You can subtract those atoms' valence electron counts from the structure to determine how many valence electrons must come from atom E:

32 - 6 - 3(7) = 32-27 = 5

So you know that element E is in the 3rd period and has 5 valence electrons. From looking at a periodic table, E must be phosphorus.

[Daria Azizad 1K]

Using formal charge is a helpful way to confirm the identity of E, as we know that an element w/ 5 VE is likely to be the central atom. We could also subtract the electrons accounted for by Cl and O from the total # of electrons and be left with 5 electrons. Since we are told that E is in period 3, we can identify is as P.