Two elements, P and Q, are in the same period. P has 1 valence electron and Q has 6 valence electrons. Which one is more reactive, and why?

Question

Accepted Answer

: Both P and Q can be reactive, but in different ways: P (with 1 valence electron, like an alkali metal) is a highly reactive metal because it easily loses its single valence electron. Q (with 6 valence electrons) is close to completing an octet and is a reactive non-metal. Generally, within the same period, elements at the extremes of valence electron count (near 1 or near 7) tend to be the most reactive, while those near a complete octet (7) are more reactive than those near a half-filled shell (like 4).