Lanthanoids (Ln) when heated with nitrogen, form compounds of the type _____.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → $LnN$
Lanthanoids (Ln, atomic numbers 58–71) are highly electropositive and reactive metals. When heated with nitrogen (typically at high temperatures), they form nitrides with the formula LnN (lanthanoid(III) nitride).
- Most lanthanoids exhibit a stable +3 oxidation state.
- The reaction is: 2Ln + N₂ → 2LnN
- These nitrides are ionic compounds with Ln³⁺ and N³⁻ ions.
Examples:
- Cerium nitride: CeN
- Lanthanum nitride: LaN
- Praseodymium nitride: PrN
Why not the others?
- Ln₂N: Would imply +1 oxidation state (unstable for lanthanoids).
- LnN₂: Would imply +4 oxidation state (rare, not typical with N₂).
- Ln₂N₃: Would imply +3 state but incorrect stoichiometry (should be 2Ln : 3N → but actual is 1:1).