Yes, MONADES is a Scrabble word!

Letter values in Scrabble US: M 3, O 1, N 1, A 1, D 2, E 1, S 1.

Is it a valid word?

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

(chemistry) an atom having a valence of one
a singular metaphysical entity from which material properties are said to derive
(biology) a single-celled microorganism (especially a flagellate protozoan)
a singular metaphysical entity from which material properties are said to derive