Using Lewis symbols, show how atoms of sulfur and sodium form ionic bonds, leading to the correct formula of sodium sulfide, Na2S.
The Correct Answer and Explanation is:
Lewis Symbols:
- Sodium (Na): 1 valence electron → Na·
- Sulfur (S): 6 valence electrons → ··S·· (with two lone pairs and two unpaired electrons)
Each sodium atom has one valence electron, and sulfur has six valence electrons. To achieve a stable octet, sulfur needs to gain two electrons. Each sodium atom can donate one electron. Therefore, two sodium atoms are needed to supply the two electrons required by one sulfur atom.
Electron Transfer:
- Each Na atom loses 1 electron:
Na· → Na⁺ + e⁻ - Sulfur gains 2 electrons:
··S·· + 2e⁻ → S²⁻
The result is the formation of a Na⁺ cation and an S²⁻ anion. Two Na⁺ ions are required to balance the −2 charge of one S²⁻ ion, leading to the chemical formula Na₂S.
Ionic Bond Formation:
After the electron transfer:
- Two Na⁺ ions are electrostatically attracted to one S²⁻ ion.
- These oppositely charged ions form strong ionic bonds, resulting in the formation of sodium sulfide.
Representation:
Na· · ·
+ · ·S·· → Na⁺ S²⁻ Na⁺
Na· · ·
Explanation:
Sodium sulfide is an ionic compound formed through the transfer of electrons between metal and nonmetal atoms. Sodium, a group 1 metal, readily loses its single valence electron to achieve a noble gas configuration. Sulfur, a group 16 nonmetal, needs two additional electrons to complete its octet. By accepting two electrons, one from each of two sodium atoms, sulfur achieves stability as a sulfide ion (S²⁻). The resulting electrostatic attraction between the positively charged sodium ions and the negatively charged sulfide ion creates a stable ionic lattice in the solid state. The formula Na₂S reflects the 2:1 ratio necessary to balance the charges of the ions involved.
