Q26 · CSIR-NET Chemistry, June 2015

Paper: CSIR-NET June 2015 · Subject: Physical Chemistry · Chapter: Atomic and Molecular Term Symbol · Topic: Term Symbols Atoms · Marks: 2 · Difficulty: Medium

The term symbol for the first excited state of Be with the electronic configuration $1 \mathrm{s}^{2} 2 \mathrm{s}^{1} 3 \mathrm{s}^{1}$ is

(a)${ }^{3} \mathrm{S}_{1}$

(b)${ }^{3} \mathrm{S}_{0}$

(c)${ }^{1} \mathrm{S}_{0}$

(d)${ }^{2} \mathrm{S}_{1 / 2}$

Answer

Answer: A ✓ checked by 4AB · confidence high

Explanation

1s²2s¹3s¹: two unpaired s electrons, L = 0, S = 1 or 0. The triplet is lower (Hund), and with L = 0 the only J is 1, so ³S₁.

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