What do you understand by isoelectronic species? Name a species that will be isoelectronic with each of the following atoms or ions. (i) F– (ii) Ar (iii) Mg2+ (iv) Rb+

🔷 What are Isoelectronic Species?

✅ Isoelectronic species are atoms or ions that have the same number of electrons, and hence the same electronic configuration, but may have different nuclear charges (atomic numbers).

🔸 They are “electronically identical,” but not chemically.

🔶 Now, let’s find one isoelectronic species for each:

(i) F⁻ (Fluoride ion):

• Atomic number of F = 9

• F⁻ has gained 1 electron → total = 10 electrons
  ✅ Isoelectronic with: Ne (Neon) (Z = 10)

(ii) Ar (Argon):

• Atomic number = 18 → 18 electrons
  ✅ Isoelectronic with: Cl⁻ (Z = 17, gains 1 e⁻ → 18 electrons)
  Or also K⁺ (Z = 19, loses 1 e⁻ → 18 electrons)

(iii) Mg²⁺ (Magnesium ion):

• Atomic number = 12, loses 2 electrons → 10 electrons
  ✅ Isoelectronic with: O²⁻ (Z = 8, gains 2 e⁻ → 10 electrons)
  Or also F⁻ or Ne

(iv) Rb⁺ (Rubidium ion):

• Atomic number = 37, loses 1 electron → 36 electrons
  ✅ Isoelectronic with: Kr (Krypton) (Z = 36)

✅ Summary Table: