Ionic bonds are formed between atoms willing to donate electrons and atoms willing to accept them. In the case of lithium, it is a metal with 1 electron in outer shell and is ready to donate it to form Li+ ion. It will readily form an ionic compound with halides.
Physical changes are typically the changes in state or phase, without formation of a new compound. That means, melting, freezing, sublimation, etc. are physical changes. Chemical changes are considered when a new compound is formed. Hence, in this case, when lithium forms ionic bonds ( such as lithium bromide or lithium chloride), we end up with a new compound (different from the reactants), and this would be considered a chemical change, and not a physical change.
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