Which of the following molecules has only ionic bonds? a) KCl c) Cl2 b) HF d) Na2SO4
The correct answer and explanation is:
The correct answer is d) Na₂SO₄ (sodium sulfate).
Explanation:
Ionic bonds form when there is a complete transfer of electrons from one atom to another, usually between metals and nonmetals, resulting in positively charged cations and negatively charged anions held together by strong electrostatic forces.
Let’s analyze each option:
a) KCl (Potassium chloride)
- K is a metal, Cl is a nonmetal.
- The bond between K and Cl is ionic because potassium donates one electron to chlorine, forming K⁺ and Cl⁻ ions.
- So, KCl contains ionic bonds between K⁺ and Cl⁻ ions.
b) HF (Hydrogen fluoride)
- Both H and F are nonmetals.
- HF has a polar covalent bond because electrons are shared unequally, with fluorine pulling electrons strongly toward itself.
- This is not an ionic bond but a covalent bond with polarity.
c) Cl₂ (Chlorine molecule)
- This is a molecule of two chlorine atoms.
- Both are the same element, sharing electrons equally.
- The bond is a nonpolar covalent bond, not ionic.
d) Na₂SO₄ (Sodium sulfate)
- Na is a metal, and SO₄ (sulfate) is a polyatomic ion made of nonmetals.
- The bond between Na⁺ ions and SO₄²⁻ ions is ionic — the metal cations interact electrostatically with the polyatomic anion.
- However, inside the sulfate ion (SO₄²⁻), the bonds between sulfur and oxygen are covalent.
- Since the question asks which molecule has only ionic bonds, strictly speaking, Na₂SO₄ contains ionic bonds between sodium and sulfate ions, but covalent bonds within the sulfate ion.
So why pick Na₂SO₄?
- KCl also contains ionic bonds only, between K⁺ and Cl⁻ ions.
- Na₂SO₄ contains ionic bonds between Na⁺ and SO₄²⁻ ions, but covalent bonds within SO₄²⁻.
- Cl₂ and HF have only covalent bonds (nonpolar and polar respectively).
If the question asks for a compound with only ionic bonds, the best strict answer is KCl because it consists purely of ionic bonds between K⁺ and Cl⁻.
If the question means “contains ionic bonds,” then both KCl and Na₂SO₄ qualify, but Na₂SO₄ has covalent bonds inside the sulfate ion.
Final clarification:
- Only ionic bonds: KCl
- Ionic + covalent bonds: Na₂SO₄
- Only covalent bonds: HF and Cl₂
Therefore, the molecule with only ionic bonds is:
a) KCl