There isn't a separate, distinct name for the empirical formula of an ionic compound. The term "empirical formula" is used universally, regardless of whether the compound is ionic or covalent.

However, it's important to note that for ionic compounds, the empirical formula already represents the simplest whole-number ratio of ions in the compound, which is also the same as the formula unit. So, you could say that the empirical formula of an ionic compound is the same as its formula unit.

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