Answer
Helium’s two electrons fill the n=1 shell. The filled shell means that helium is satisfied, and does not tend to bond with other atoms.
On the other hand, lithium has two electrons in the n=1 shell, and the third electron is in the n=2 shell. That shell can hold 8 electrons. This makes lithium very reactive with other elements. This chapter discusses the concept of electron shells, not Chapter 11.
Work Step by Step
This may be found on pages 216 and 608.
