[wat10000]

Because it rapidly steals electrons, it becomes inert quickly. Helium you find lying around will be inert. Helium that has just shot out from the radioactive decay of an unstable atom will not be inert.

[chii]

I would imagine that an alpha particle would still be inert in the sense that it won't cause chemical reactions with other molecules.

[kergonath]

Stealing electrons is a chemical reaction.