What is the formula for an ionic compound made of aluminum and oxygen? A) AlO2 B) Al2O3 C) Al3O2 D) AlO E) none of the above
The Correct Answer and Explanation is:
Correct Answer: B) Al₂O₃
Explanation:
To determine the correct formula of an ionic compound formed between aluminum and oxygen, we must consider the charges of the ions involved.
Step 1: Determine the Ions
- Aluminum (Al) is a metal found in Group 13 of the periodic table. It tends to lose 3 electrons to form a +3 cation (Al³⁺).
- Oxygen (O) is a non-metal in Group 16. It tends to gain 2 electrons to form a −2 anion (O²⁻).
Step 2: Balance the Charges
An ionic compound must be electrically neutral, meaning the total positive charge must balance the total negative charge.
Let’s use the criss-cross method to find the lowest ratio of ions that balances the charges:
- Al³⁺ and O²⁻
- Cross the charges to find the subscripts:
- Al: 2 (from O’s charge)
- O: 3 (from Al’s charge)
This gives us the formula Al₂O₃.
Step 3: Verify Neutrality
- 2 aluminum ions: 2 × (+3) = +6
- 3 oxide ions: 3 × (−2) = −6
- Total charge = +6 − 6 = 0
So, Al₂O₃ is a neutral compound, making it the correct formula.
Step 4: Why Other Choices Are Incorrect
- A) AlO₂: Implies a +3 aluminum with two oxide ions, but the total charge would be −4 + 3 = −1, not neutral.
- C) Al₃O₂: Charges would be 3×(+3) = +9, and 2×(−2) = −4, total = +5, not neutral.
- D) AlO: +3 and −2 gives total = +1, not neutral.
- E) none of the above: Incorrect, because B is correct.
Thus, the correct formula is B) Al₂O₃.
