Identify among the following which has Lowest energy of electron in 1st shell.
Correct answer: D. Be+³
- A. H
- B. He+¹
- C. Li+²
- D. Be+³
Explanation
For a hydrogen-like species in the first shell, electron energy is E = -13.6 Z^2/1^2 eV, so it becomes more negative as nuclear charge Z increases. Be3+ has Z = 4 and therefore the lowest energy, E = -13.6 x 4^2 = -217.6 eV, compared with -13.6 eV for H. The likely mistake is choosing H because it is the simplest atom, while ignoring the stronger attraction of the higher nuclear charge in these one-electron ions.
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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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