What is the correct formula for the compound iron(III) nitride?
a) Fe3N
b) FeN3
c) FeN
d) Fe2N3
e) Fe3N2
The correct answer and explanation is :
The correct formula for the compound iron(III) nitride is e) Fe₃N₂.
Explanation:
Iron(III) nitride refers to a compound formed between iron and nitrogen, where iron has a +3 oxidation state. To determine the correct chemical formula, we need to use the principles of charge balance between the ions of iron (Fe) and nitrogen (N).
- Iron(III) ion (Fe³⁺): The “III” in iron(III) indicates that iron is in the +3 oxidation state. Therefore, each iron ion has a charge of +3.
- Nitride ion (N³⁻): Nitrogen typically forms a nitride ion with a charge of -3. This is because nitrogen needs three additional electrons to complete its valence shell, giving it a -3 charge.
Now, to form a neutral compound, the total positive charge must balance the total negative charge. This means that the number of iron ions and nitrogen ions must combine in such a way that their charges cancel out.
Let’s analyze the possible combinations:
- In Fe₃N₂, we have 3 iron (Fe³⁺) ions, each with a +3 charge, for a total of +9.
- We have 2 nitrogen (N³⁻) ions, each with a -3 charge, for a total of -6.
This gives us a total charge of +9 (from iron) and -6 (from nitrogen). In order to balance this, the compound needs to have a ratio of 3 iron ions to 2 nitrogen ions, ensuring that the charges cancel out in the simplest form (3 × +3 = 9 and 2 × -3 = -6).
Therefore, the correct formula for iron(III) nitride is Fe₃N₂.
The other options are incorrect because:
- Fe₃N would imply a mismatch in the charges, with 3 irons and only 1 nitrogen, which wouldn’t balance the charges.
- FeN₃ would imply 1 iron for every 3 nitrogens, which does not match the iron(III) oxidation state.
- FeN or Fe₂N₃ also result in charge imbalances for the iron(III) and nitride ions.