Yes, RADICALS is a Scrabble word!

Letter values in Scrabble US: R 1, A 1, D 2, I 1, C 3, A 1, L 1, S 1.

Is it a valid word?

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

(chemistry) two or more atoms bound together as a single unit and forming part of a molecule
an atom or group of atoms with at least one unpaired electron; in the body it is usually an oxygen molecule that has lost an electron and will stabilize itself by stealing an electron from a nearby molecule
a person who has radical ideas or opinions
(mathematics) a quantity expressed as the root of another quantity
a character conveying the lexical meaning of a logogram
(linguistics) the form of a word after all affixes are removed

Also: chemical group, free radical, root word.