[Ar]4s^2 3d^10 4p^4 is the noble gas configuration of which element?

1 Answer
Truong-Son N.
Dec 31, 2016

That's not a noble gas configuration. That is, however, a noble gas shorthand for the electron configuration of selenium.

Notice how the number of electrons corresponds to the number of protons in a neutral element. Thus, if you start from the [Ar] portion of the electron configuration, you should have accounted for 18 electrons.

In fact, the noble gas portion of the configuration represents the core electrons of the unidentified element. Therefore, everything after it is non-core (the 4s and 4p electrons are your valence electrons here, for the post-transition elements on the fourth row).

Again, since the number of electrons equals the number of protons in a neutral element, and there are two 4s, ten 3d, and four 4p electrons, there must be

18 + 2 + 10 + 4 = 34

total electrons in the element, which correspond to 34 total protons in the element. When you look it up, you should locate selenium and find that it has atomic number 34.

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