1. Convert grams to moles:

* Hydrogen: 4.0 g H / 1.008 g/mol H = 3.97 mol H

* Nitrogen: 28 g N / 14.01 g/mol N = 1.99 mol N

2. Find the mole ratio:

* Divide the number of moles of each element by the smallest number of moles (1.99 mol N in this case).

* Hydrogen: 3.97 mol H / 1.99 mol N ≈ 2

* Nitrogen: 1.99 mol N / 1.99 mol N ≈ 1

3. Write the empirical formula:

* The mole ratio tells us the simplest whole-number ratio of atoms in the compound.

* The empirical formula is H₂N.

Therefore, the empirical formula of the compound is H₂N.