Grouping of Valence Electrons [ENDORSED]

[Parsia Vazirnia 2L]

Hello,

I am looking at an example on page 48 that says that lead has the same number of valence electrons as carbon. The electron configuration for lead is [Xe]4f^14,5d^10,6s^2,6p^2. I understand that the f,d, and s orbitals have their orbital filled so you would just re write lead as [Hg]6p^2. Why does lead have 4 valence electrons and not 2? (6p^2).

[Amir Patel 1G]

Hello Parsia,

Pb has 4 valence electrons since its valence shell (n=6) has 4 electrons. The 6s and 6p sub-shells are both holding 2 electrons, which means the 6s orbital is full, but the 6p orbitals still have room for 4 additional electrons.

[Jasleen Kaur 1J]

Hey there,
I am not quite understanding why the the valence electrons are 4. Could you expand on that explanation please.

[Pauline Tze 3B]

Hi Jasleen,

If you observe the electron configurations on the periodic table, you would notice that valence electrons come from the s- and p-orbitals of the highest energy shell for a given element (for the s and p blocks). The s orbital can hold 2 and the p orbital can hold 6 which add up to 8 (for 8 valence electrons).

For lead, if you look at the noble gas core abbreviated electron configuration: it is, as you said, [Xe]4f^14,5d^10,6s^2,6p^2
since the shell is n=6, we pay attention to 6s^2 and 6p^2 which add up to 4 electrons, for a total of 4 valence electrons. However, between the s and p orbitals, we have room for a total of 8 valence electrons. Like what Amir said, the 6s orbital (which can only hold 2 electrons) is full, but 6p (which can hold 6 electrons) has room for 4 more electrons.

I hope that helps!