* Sodium (Na) is in group 1 of the periodic table, meaning it has a +1 charge as an ion (Na⁺).
* Phosphorus (P) is in group 15 of the periodic table, meaning it has a -3 charge as an ion (P³⁻).
To create a neutral compound, you need three sodium ions (3 x +1 = +3) to balance out one phosphide ion (-3).
