Yes, INTONATION is a Scrabble word!

Letter values in Scrabble US: I 1, N 1, T 1, O 1, N 1, A 1, T 1, I 1, O 1, N 1.

Is it a valid word?

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

rise and fall of the voice pitch
singing by a soloist of the opening piece of plainsong
the act of singing in a monotonous tone
the production of musical tones (by voice or instrument); especially the exactitude of the pitch relations

Also: pitch contour.