Na2S is named
A) sodium disulfide.
B) sodium sulfide.
C) sodium(lII) sulfide.
D) sodium sulfur.
The correct answer and explanation is :
The correct answer is:
B) sodium sulfide.
Explanation:
Sodium sulfide (Na₂S) is an ionic compound composed of sodium (Na) and sulfur (S). To determine its correct name, let’s analyze its chemical composition and the systematic naming rules.
Step 1: Identifying the Elements
- Sodium (Na): Sodium is an alkali metal in Group 1 of the periodic table. It forms a +1 charge as a cation (Na⁺).
- Sulfur (S): Sulfur is a non-metal in Group 16 (chalcogens) and commonly forms a -2 charge as an anion (S²⁻).
Step 2: Balancing the Charges
Since sodium has a +1 charge and sulfur has a -2 charge, two sodium ions (2 × Na⁺) are required to balance one sulfide ion (S²⁻), forming Na₂S.
Step 3: Naming the Compound
According to IUPAC nomenclature for binary ionic compounds:
- The cation (metal) is named first using its elemental name → Sodium.
- The anion (non-metal) is named second with an “-ide” suffix → Sulfide.
Thus, Na₂S is named “sodium sulfide”.
Why the Other Choices Are Incorrect?
- A) Sodium disulfide → Incorrect because “disulfide” (S₂²⁻) refers to a different polyatomic ion (S₂²⁻), not the simple sulfide ion (S²⁻).
- C) Sodium(III) sulfide → Incorrect because sodium only forms a +1 charge, so no Roman numeral is needed.
- D) Sodium sulfur → Incorrect because ionic compounds do not use element names directly without proper suffixes.
Thus, sodium sulfide (Na₂S) is the correct name.