Identifying elements in Lewis structures [ENDORSED]

[Toru Fiberesima 1L]

For question 3.37, why would the answer be phosphorus specifically and not, say nitrogen, or any of the other period 3 elements. Would they not all work due to having 5 valence electrons. In general, how does one figure out an unknown element from a lewis structure?

[Luis Avalos 1D]

It specifically says "period 3 element" which is Na through Ar, and nitrogen is a period 2 element. On top of this, the central atom does not strictly follow the octet rule which is also an indication that it would not be nitrogen.

[nicolesalcedo]

Lavelle hasn't gone over this so I'm not 100% certain, but I would use the charges of the known elements in the lewis structure, count the number of shared electrons/bonds the central element has, and count the total number of electrons the lewis structure contains. I think all of these would help specify the unknown element.