Final answer:
The chemical formula for the ionic compound formed between a lithium ion and a peroxide ion (O₂²-) is Li₂O₂.
Step-by-step explanation:
Predicting the Formula for the Ionic Compound of Lithium and Peroxide
The chemical formula for the ionic compound formed between lithium ion and peroxide ion, O₂²-, is Li₂O₂. Lithium (Li) has a +1 charge, and peroxide (O₂²-) has a -2 charge. Using the crisscross method, we determine that two lithium ions are needed to balance the charge of one peroxide ion, which gives us the formula Li₂O₂. It's important to remember that when writing formulas, the numerical values of the ion charges are used as subscripts for the other ion, and these subscripts should be in their lowest whole number ratio. As peroxide is a diatomic ion, the compound does not follow the standard simplest form rule for binary ionic compounds and thus retains its peroxide identity in the compound.