1. The problem states that an element with atomic number 11 combines with nitrogen to form a compound. 2. Atomic number 11 corresponds to sodium (Na). 3. Nitrogen typically forms ions with a charge of $3-$ (nitride ion, $\text{N}^{3-}$). 4. Sodium forms ions with a charge of $1+$ (sodium ion, $\text{Na}^+$). 5. To form a neutral compound, the total positive charge must balance the total negative charge. 6. Since nitrogen has a charge of $3-$, and sodium has a charge of $1+$, three sodium ions are needed to balance one nitride ion. 7. Therefore, the formula of the compound formed is $\text{Na}_3\text{N}$. Final answer: $\text{Na}_3\text{N}$