Asked in Premeth MDCAT 2025 — Work and Energy, Atomic Structure, Nouns 2025Moderate

What is the electron configuration of Ga3+ ion

Correct answer: B. 1s2 2s2 2p6 3s2 3p6 3d10

  • A. 1s2 2s2 2p6 3s2 3p6 3d10 4s2
  • B. 1s2 2s2 2p6 3s2 3p6 3d10
  • C. 1s2 2s2 2p6 3s2 3p6 3d9 4s2
  • D. 1s2 2s2 2p6 3s2 3p5 3d10 4s2

Explanation

The electron configuration of neutral gallium (Ga) is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p1. When forming the Ga3+ ion, electrons are removed from the outermost orbitals first. Therefore, the electrons in the 4p and 4s orbitals are removed, resulting in the electron configuration 1s2 2s2 2p6 3s2 3p6 3d10. The other options incorrectly remove electrons from the 3d or 3p orbitals, which are not the outermost orbitals for Ga.

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Electronic configuration describes how electrons occupy shells, subshells and orbitals around an atom. Questions use the Aufbau principle, Pauli exclusion principle and Hund's rule to write configurations, identify valence electrons, form ions and explain periodic trends, including common exceptions such as chromium and copper.

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