Yes, POLYVALENCE is a Scrabble word!

Letter values in Scrabble US: P 3, O 1, L 1, Y 4, V 4, A 1, L 1, E 1, N 1, C 3, E 1.

Is it a valid word?

POLYVALENCE is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

(chemistry) the state of having a valence greater than two
(toxicology) the state of being capable of counteracting more than one toxin or antigen or kind of microorganism

Not playable in Scrabble US: POLYVALENCY, MULTIVALENCY.