When potassium reacts with arsenic to form an ionic compound, each metal atom loses 1 electron(s) and each nonmetal atom gains 3 electron(s). There must be 3 potassium atom(s) for every 1 arsenic atom(s) in the reaction.
Explanation:
We need to consider the octet rule: each atom will gain or lose electrons to have 8 electrons in its valence shell.
Potassium is in Group 1, so it has 1 valence electron, which will lose to form K⁺.
Arsenic is in Group 15, so it has 5 valence electrons. Then, it will gain 3 electrons to form As³⁻.
To have an electrical molecule between K⁺ and As³⁻, we require 3 K⁺ and 1 As³⁻, and the resulting formula is K₃As.
