Lithium compounds are generally not unstable, in fact, they are quite stable. Lithium is the lightest metal and has the smallest atomic radius, which allows it to form strong ionic bonds with other elements. This results in the formation of stable compounds.

However, there are some exceptions to this rule. For example, lithium nitride (Li3N) is a highly unstable compound that can easily decompose to form lithium and nitrogen gas. This is due to the fact that the nitrogen atom in Li3N is in a very high oxidation state (+3), which makes it unstable.

Another example of an unstable lithium compound is lithium acetylide (LiC2H2). This compound is also highly reactive and can easily decompose to form lithium carbide (Li2C2) and hydrogen gas. This is due to the fact that the acetylide ion (C2H2^2-) is a very strong reducing agent, which means that it has a strong tendency to donate electrons.

In general, lithium compounds are quite stable, but there are a few exceptions to this rule. These exceptions are usually due to the fact that the lithium atom is in a high oxidation state or that the compound contains a strong reducing agent.