Question

free response question--worth 10 points
why does helium only have 2 valence electrons rather than 8 as its group number would imply?
use at least two complete sentences in your answer and use the following words.
word bank
group number
valence electrons
orbital
electrons

Explanation:

Helium is in Group 18 (noble gases). Its valence electrons are in the first orbital (\(1s\)). The first orbital can hold a maximum of 2 electrons. So, it has 2 valence electrons instead of 8 (which is the case for elements with valence electrons in the second or higher orbitals like \(n = 2,3,\cdots\) where the outermost orbital can hold 8 electrons).

Answer:

Helium is in Group 18. Its valence electrons are in the first orbital (\(1s\)) which can hold only 2 electrons. Other group - 18 elements (with valence electrons in \(n\geq2\) orbitals) have 8 valence electrons as their outermost orbital (\(s^{2}p^{6}\)) can hold 8 electrons.