How to tell which ionic bond is stronger: BaCl2, LiF, NaBr, or KI?
The correct answer and explanation is:
The strongest ionic bond among BaCl₂, LiF, NaBr, and KI is in LiF (lithium fluoride).
Explanation:
Ionic bond strength depends mainly on the electrostatic force of attraction between the positively charged cation and the negatively charged anion. According to Coulomb’s law, this force is directly proportional to the product of the charges and inversely proportional to the square of the distance between the ions.
- Charge of ions:
- BaCl₂ contains Ba²⁺ and Cl⁻ ions. The charge product is 2×1=22 \times 1 = 2.
- LiF contains Li⁺ and F⁻ ions, with a charge product of 1×1=11 \times 1 = 1.
- NaBr contains Na⁺ and Br⁻ ions, charge product 1×1=11 \times 1 = 1.
- KI contains K⁺ and I⁻ ions, charge product 1×1=11 \times 1 = 1.
Although BaCl₂ has a higher charge product due to Ba²⁺, bond strength is also strongly affected by ion size and distance between ions.
- Ionic radii and distance between ions:
Smaller ions attract more strongly because the distance between the centers of ions is smaller. The sizes of ions from smallest to largest are:- Cations: Li⁺ < Na⁺ < K⁺ < Ba²⁺
- Anions: F⁻ < Cl⁻ < Br⁻ < I⁻
- Balancing charge and size:
Ba²⁺ has a +2 charge, which tends to increase attraction, but Ba²⁺ is much larger than Li⁺, which increases the distance between Ba²⁺ and Cl⁻ ions. Larger ionic radii reduce bond strength. LiF, despite having monovalent ions, consists of very small ions (Li⁺ and F⁻), resulting in a very short distance between ions. This small distance strongly enhances the electrostatic attraction. - Lattice energy perspective:
Lattice energy is a measure of bond strength in ionic solids. LiF has one of the highest lattice energies among these compounds because of the small sizes and strong attraction. - Conclusion:
While BaCl₂ benefits from a higher charge on the cation, the large size of Ba²⁺ and Cl⁻ reduces bond strength. LiF’s very small ions make the ionic bond strongest overall.
Summary:
LiF forms the strongest ionic bond due to the combination of small ionic radii and strong electrostatic attraction. This makes its bond stronger than in BaCl₂, NaBr, or KI.