Dec 09, 2021 · Aluminum belongs to Group 3A, so its ion will be Al3+. On the other hand, oxygen is in Group 6A, making it O2–. Whenever we combine to ions of opposing charges to form a compound, we need to exchange their numbers, like so: So the formula of the ionic compound is Al2O3, aluminum oxide. See also what is the smallest mountain in the world.
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