The name of the ionic compound with the formula Rb3P is:
1) Trirubidium phosphide
2) Rubidium phosphide
3) Rubidium (1) phosphide
4) Rubidium (III) phosphide
The correct answer and explanation is :
The correct answer is:
(2) Rubidium phosphide
Explanation:
Understanding Ionic Compounds
Ionic compounds are named by identifying the cation (positively charged ion) first and then the anion (negatively charged ion). The metal typically forms a cation, while the nonmetal forms an anion. In this case, we have Rb (Rubidium) and P (Phosphorus).
Step 1: Identify the Ions
- Rubidium (Rb) is an alkali metal (Group 1), which always forms a +1 charge (Rb⁺).
- Phosphorus (P) typically forms a -3 charge (P³⁻) when it becomes an anion (phosphide ion).
Step 2: Balance the Charges
To ensure the compound is electrically neutral, we need three Rb⁺ ions to balance the -3 charge of one P³⁻ ion. This gives us the formula Rb₃P.
Step 3: Name the Compound
- The cation (rubidium) is simply named “rubidium” because it has a fixed oxidation state (+1) and does not require a Roman numeral.
- The anion (phosphide) follows the rule of changing the element name from “phosphorus” to “phosphide.”
Thus, the correct name is Rubidium phosphide.
Why Are the Other Options Incorrect?
1) Trirubidium phosphide → Incorrect because prefixes (like “tri-“) are not used in ionic compound names.
2) Rubidium phosphide → Correct, as explained.
3) Rubidium (I) phosphide → Incorrect because rubidium always has a +1 charge, so the Roman numeral is unnecessary.
4) Rubidium (III) phosphide → Incorrect because rubidium does not form a +3 charge.
Conclusion
The correct name for Rb₃P is Rubidium phosphide, following standard ionic naming conventions.