Yes, EXCEPTION is a Scrabble word!

Letter values in Scrabble US: E 1, X 8, C 3, E 1, P 3, T 1, I 1, O 1, N 1.

Is it a valid word?

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

a deliberate act of omission
an instance that does not conform to a rule or generalization; the only exception was her last child"
grounds for adverse criticism