Question

What is the correct Lewis structure for arsenic?

Answer 1

Arsenic is isoelectronic with nitrogen (they are both Group V elements), so there are 5 valence electrons.

Explanation:

Look at the position of arsenic in the Periodic Table. It is under phosphorus, which is under nitrogen. These elements are thus isoelectronic, and their chemistry should be similar to a first approximation.

Consider ammonia versus phosphine versus arsine, i.e. `NH_3` versus `PH_3` versus `AsH_3`. All of these hydrides have a formal lone pair of electrons, and should thus be isostructural.