enough of a thing

Not enough [theoretical "of" here] money.
Не хватает денег.

мне тебя́ не хвата́ет‎ - There's not enough of you for me (overliteral)
э́того ему́ хва́тит на ме́сяц‎ ― "it will last him a month" - Of this for him there is enough for a month

The thing, OF which there is enough is in genitive.

According to wikipedia, this meaning of хватать is impersonal, and thus can only be used/found in:
хватает
хватит, будет хватать
хватило and хватало

All singular third person.

у него́ ша́риков не хвата́ет‎ (colloquial) - he is not all there. Seems to be similar to English "He's lost his marbles."

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Хватать/схватить/хватить can also mean grasp or grab. It's separate, and used quite standardly.