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A question asks:

This question refers to isolated gaseous atoms. In which atom are all electrons paired? Ba, Br, S or Si?

I thought it was Ba as its electron configuration is [Xe] 6s2.

However, the answer says Si, which seems incorrect to me.

Could someone please confirm the answer for me?

Thanks

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    $\begingroup$ Si seems incorrect to me as well. $\endgroup$ – Ivan Neretin Feb 23 at 7:15
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The configuration for the free atoms is:

  • Ba - $\mathrm{[Xe]\ 6s^2}$
  • Br - $\mathrm{[Ar]\ 3d^{10} 4s^2 4p^5}$
  • S - $\mathrm{[Ne]\ 3s^2 3p^4}$
  • Si - $\mathrm{[Ne]\ 3s^2 3p^2}$

Thus:

  • Barium has no unpaired electrons.
  • Bromine has one unpaired electron in 4p subshell.
  • Sulfur has two unpaired electrons in the 3p subshell.
  • Silicon has two unpaired electrons in the 3p subshell.
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