Question

Which of the following elements has the highest first ionization energy?

• A. Sodium
• B. Magnesium
• C. Aluminum
• D. Silicon

Hint:

\textbf{Key Fact:} Ionization energy increases across a period due to increased nuclear charge, with minor dips at group transitions.

Answer 1

The Correct Option is D

• Trend in Ionization Energy: Ionization energy generally increases across a period (left to right) in the periodic table due to increasing nuclear charge and decreasing atomic radius.
• Position in Periodic Table: All elements are in Period 3:
  • Sodium (Na): Group 1
  • Magnesium (Mg): Group 2
  • Aluminum (Al): Group 13
  • Silicon (Si): Group 14
• Compare Ionization Energies: Moving from Na to Si, ionization energy increases:
  • Sodium has the lowest ionization energy (single electron in outer shell).
  • Magnesium has a higher ionization energy than sodium (more protons, higher effective nuclear charge).
  • Aluminum has a slightly lower ionization energy than magnesium due to the electron being removed from a p-orbital (less tightly held than an s-orbital).
  • Silicon has the highest ionization energy among these due to its position furthest to the right in the period.
• Conclusion: The correct answer is (4) Silicon.