Yes, DIAZONIUM is a Scrabble word!

Letter values in Scrabble US: D 2, I 1, A 1, Z 10, O 1, N 1, I 1, U 1, M 3.

Is it a valid word?

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

the univalent cation R-N:N- (where R is an aromatic hydrocarbon); found in salts that are used in manufacturing azo dyes