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

1 Answer
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#.