Is it true to say that if an atom has a valence of 1, 2, or 3 it will be stable as a cation?

Question

and if it has a valence of 4, 5, 6, or 7 it wil be stable as an anion?

Answer 1

First part: No. Valence is a number of bonds formed with itself or other elements. Cl has a valence of 1. Sulfur in sulfides has a valence of 2. Nitrogen in ammonia has a valence of 3. But none of those elements form common cations.

Second part: Problematical. Carbon has a valence of 4, but forms only two true carbides, Al4C3 and Be2C. Phosphorus has valence 5 in PCl5, but... Sulfur hexafluoride exists, and sulfur forms S= anions.

I wonder if you meant to ask about oxidation numbers? "Is it true to say that if an atom can have oxidation numbers of +1, +2, or +3, it will be stable as an cation?" That's probably true. "...and if it can have oxidation numbers of +4, +5, +6, or +7, it will be stable as an anion?" That also seems true for main group elements (IV, V, VI, and VII on the periodic table.