Question

What is the correct order of size from smallest to largest of K K+ Ca and Ca2 +?

Answer 1

The atomic numbers of the ions are S (16), Cl (17), K (19), and Ca (20). Thus, the ions decrease in size in the order S2– > Cl– > K+ > Ca2+.

Answer 2

Correct of atomic size in K, K⁺, Ca and Ca⁺²

Explanation:

• First decide the greater atomic size in K and Ca, since K and Ca belongs to same period elements. So, factors which dominates is effective nuclear charge. As we go from left to right there will be increase in effective nuclear charge and thus attraction between the valence shell electron and a nucleus increases which means atomic size decreases.
• So, size of calcium decreases than potassium as effective nuclear charge increases in calcium due to which size decreases.
• Now, size of cations are smaller than their parent atoms because when an atom losses electrons that means number of protons will be greater than number of electrons due to which atom is not neutral anymore. So, size decreases.
• Therefore, K⁺ is smaller than K and Ca⁺² is smaller than Ca.
• So, its correct order is Ca⁺²< Ca < K⁺ < K.