Determine the formula unit for the compound formed when each pairs of ions interact.

Question

Determine the formula unit for the compound formed when each pairs of ions interact.

1. Li^+ and O2^−: ?
2. Mg^2+ and S2^−:
3. Al^3+ and Cl^−:
4. Na^+ and N^3−:

Answer 1

Here the numbers in the formula unit for the compound come from just balancing charge. Note below that

1. the subscript 1 is never included in a formula.
2. the cation (positively charged ion) always comes first in the formula

1. Li⁺ and O²⁻: 2 Li⁺ to balance one O²⁻ gives the formula Li₂O

1. Mg²⁺ and S²⁻: One Mg²⁺ to balance one S²⁻gives the formula MgS

1. Al³⁺ and Cl⁻: 3 Cl⁻ to balance one Al³⁺ gives the formula AlCl₃

1. Na⁺ and N³⁻: 3 Na⁺ to balance one N³⁻ gives the formula Na₃N