Video Transcript
Which of the following represents
the correct filling of electrons in the energy levels of an oxygen ion O2−?
We’ve been given five energy level
diagrams labeled from (A) to (E). Each energy level diagram shows the
electronic configuration for each atom or ion. The electronic configuration is the
distribution of electrons in energy levels. So, how do electrons distribute
themselves in energy levels? Electrons fill energy level K
first. Once K is full, the remaining
electrons fill energy level L. They then fill energy levels M and
N in turn. Each energy level holds a different
maximum number of electrons. The first level can hold a maximum
of two electrons. The second, third, and fourth
energy levels hold a maximum of eight, 18, and 32 electrons, respectively.
Now that we know how electrons fill
energy levels, we need to know how many electrons are in an O2− ion. The symbol for oxygen tells us that
a neutral atom has eight electrons. But we want to know the number of
electrons in an oxygen ion. The charge indicates that an oxygen
ion contains two more negatively charged electrons than an oxygen atom. Thus, in total, an oxygen ion
contains 10 electrons. The first two of the 10 electrons
fill energy level K. The remaining eight electrons fill
energy level L. Thus, the electronic configuration
is 2,8. And the energy level diagram which
represents the correct filling of electrons in the energy levels of an oxygen ion
O2− is (B).