Making a an area of effect work (pls help)

Basically, i want to make a mustard gas grenade, problem is, i have no idea how, i mean, i made a ranged item, but now i need to know how to make a cloud of particles that give an area of effect, ive never coded with java but if required i will.

Edit 1:
so change of plans
i got the particles working, its fine, but now theres a new problem
idk how to make an area of effect
please help

Edit 2:
another thing, it gives you potion effects, but it does it to the thrower, not in the area the grenade lands, that info seems important