* Astatine's Instability: Astatine is a highly radioactive element with a very short half-life. It's extremely rare and difficult to work with.
* Reactivity: Astatine is highly reactive and tends to form unstable compounds. It's unlikely to form a stable salt with ammonium (NH₄⁺).
Therefore, it's not possible to write a chemical formula for ammonium astatide, as the compound likely doesn't exist in a stable form.
