Yes, BISMUTH is a Scrabble word!

Letter values in Scrabble US: B 3, I 1, S 1, M 3, U 1, T 1, H 4.

Is it a valid word?

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

a heavy brittle diamagnetic trivalent metallic element (resembles arsenic and antimony chemically); usually recovered as a by-product from ores of other metals

Also: atomic number 83.