Here's why:

* NH4+ is the ammonium ion: It's a positively charged polyatomic ion formed by the combination of ammonia (NH3) and a hydrogen ion (H+).

* H- is the hydride ion: It's a negatively charged ion consisting of a single hydrogen atom.

To form a stable compound, you need a balance of positive and negative charges. Since both NH4+ and H- are positively charged, they wouldn't naturally combine.

Instead of NH4H, you might be thinking of:

* NH4Cl: Ammonium chloride, which is a common salt formed by the reaction of ammonium ions (NH4+) with chloride ions (Cl-).

* NH3: Ammonia, which is a neutral molecule.

Let me know if you have any other chemical formulas you'd like help with!