Final answer:
The formula for an ionic compound composed of sodium and phosphorus is Na3P, and for aluminum and bromine, it is AlBr3, based on the charges of the ions to ensure neutrality.
Step-by-step explanation:
To write the formula for ionic compounds we must consider the charges of the ions to ensure they balance each other out. For example:
- Sodium (Na) has a charge of +1 and phosphorus (P) has a common charge of -3 when forming an ionic compound, so the formula will be Na3P, where three sodium ions balance out one phosphorus ion.
- Aluminum (Al) has a charge of +3 and the bromide ion (Br) has a charge of -1, so the formula for aluminum bromide will be AlBr3, as one aluminum ion balances out three bromide ions.