Question

The size of isoelectronic species - F^-, Ne and Na⁺ is affected by

• A. Nuclear charge (Z )
• B. Valence principal quantum number (n)
• C. Electron-electron interaction in the outer orbitals
• D. None of the factors because their size is the same.

Answer 1

The Correct Option is A

Concept of Isoelectronic Species: Isoelectronic species are ions or atoms that have the same number of electrons. In this case, F^-, Ne, and Na⁺ all have 10 electrons.

Factors Affecting the Size of Isoelectronic Species: The size is primarily influenced by the nuclear charge (Z). The nuclear charge is the total charge of all the protons in the nucleus, which affects how strongly electrons are pulled toward the nucleus.

1. Nuclear Charge (Z): The higher the nuclear charge, the stronger the attraction between the nucleus and the electrons, leading to a smaller atomic or ionic size.
   • For F^-, the nucleus has 9 protons.
   • For Ne, the nucleus has 10 protons.
   • For Na⁺, the nucleus has 11 protons.
2. Valence Principal Quantum Number (n): All these species have electrons in the same principal quantum level, hence this does not differ.
3. Electron-Electron Interaction: This generally affects properties within different isoelectronic series but does not explain size differences better than nuclear charge.
4. None of the factors because their size is the same: This cannot be true as they have different sizes due to differing nuclear charges.

Conclusion: The correct answer is Nuclear charge (Z) because it directly influences the size of these isoelectronic species by determining how strongly electrons are attracted to the nucleus.