Si, Br ionic covalent Si, Br SiBr, silicon bromide SiBr3, silicon tribromide SiBr4, silicon tetrabromide SiqBr, silicon tetrabromide This question has multiple parts. Work all the parts to get the most points. For each of the following pairs of elements, state whether the binary compound formed is likely to be ionic or covalent. Also, choose the formula and name of the compound.
Na, S ionic covalent Na, S Na2S, sodium sulfide NaS2, sodium nitrate Na2S, sodium sulfate NaS, sodium sulphide
The Correct Answer and Explanation is:
Correct Answer:
- Type of Bond: Ionic
- Chemical Formula and Name: Na₂S, sodium sulfide
When determining whether a binary compound is ionic or covalent, the key factor lies in the types of elements involved—specifically, whether the elements are metals or nonmetals:
- Ionic bonds typically form between a metal and a nonmetal, where electrons are transferred from the metal to the nonmetal.
- Covalent bonds usually form between two nonmetals, where electrons are shared between atoms.
In the given pair—Na (sodium) and S (sulfur)—we have:
- Sodium (Na): An alkali metal in Group 1 of the periodic table. It has one valence electron and a strong tendency to lose that electron, forming a +1 cation (Na⁺).
- Sulfur (S): A nonmetal in Group 16, with six valence electrons. It needs two more electrons to complete its octet and tends to form a –2 anion (S²⁻).
When sodium and sulfur react, each sulfur atom can accept two electrons, meaning two sodium atoms are required to donate one electron each. This results in the compound:
- Na₂S, composed of two Na⁺ ions and one S²⁻ ion, making the compound electrically neutral.
Because this compound involves the transfer of electrons from metal to nonmetal, it is ionic in nature.
Now let’s evaluate the name:
- The cation (Na⁺) is sodium.
- The anion (S²⁻) is derived from sulfur, so it becomes sulfide in naming conventions.
Therefore, the correct name of the compound is sodium sulfide.
Incorrect Options:
- NaS2 is chemically incorrect—sodium doesn’t form a +2 ion to balance two sulfurs.
- NaS, sodium sulphide is incorrect because it doesn’t maintain charge balance (Na⁺ and S²⁻).
- Na₂S, sodium sulfate is incorrect—sulfate refers to SO₄²⁻, not S²⁻.
- The spelling “sulphide” is a British variant; “sulfide” is more widely accepted in scientific contexts, especially in the U.S.
Summary:
- Bond Type: Ionic
- Correct Formula: Na₂S
- Correct Name: Sodium sulfide
