Which of the following pairs would have the greatest coulombic attraction in a solid compound? 1. mg2+, S2- 2. mg2+, se2- 3.mg2+, O2-
The Correct Answer and Explanation is:
The correct answer is Option 3: Mg²⁺ and O²⁻.
Explanation:
Coulombic attraction refers to the electrostatic force between positively and negatively charged ions, which depends on two key factors: the charge of the ions and the distance between them (which is influenced by the size of the ions). The force can be described by Coulomb’s Law:
[
F = \frac{{k \cdot |q_1 \cdot q_2|}}{{r^2}}
]
Where:
- (F) is the force of attraction,
- (k) is Coulomb’s constant,
- (q_1) and (q_2) are the charges of the ions,
- (r) is the distance between the ions (related to their ionic radii).
Analyzing the Options:
- Mg²⁺ and S²⁻:
Magnesium (Mg) has a +2 charge, and sulfur (S) has a -2 charge. While both ions have relatively large charges, sulfur’s ionic radius is relatively larger than that of oxygen or selenium. This means that the distance between the ions will be greater, which results in a weaker Coulombic attraction compared to pairs with smaller ions. - Mg²⁺ and Se²⁻:
Selenium (Se) also has a -2 charge, similar to sulfur, but it has a larger ionic radius than sulfur. As a result, the distance between the Mg²⁺ and Se²⁻ ions will be even larger, leading to a weaker Coulombic attraction than between Mg²⁺ and O²⁻. - Mg²⁺ and O²⁻:
Oxygen (O) has a -2 charge, and it has the smallest ionic radius among the three anions (S²⁻, Se²⁻, O²⁻). Magnesium’s ionic radius is relatively small as well. Because of the smaller size of the ions, the distance between Mg²⁺ and O²⁻ ions will be the smallest, resulting in the greatest Coulombic attraction. Additionally, the +2 and -2 charges are strong, further contributing to a stronger attraction.
Conclusion:
The Coulombic attraction is strongest between Mg²⁺ and O²⁻ because the ions are both small in size, leading to a short distance between them and a stronger electrostatic force of attraction. Therefore, Option 3 is the correct answer.