Video Transcript
A magnesium ion contains two fewer
electrons than an atom of magnesium. If the atomic number of magnesium
is 12, which of the following energy level diagrams shows the correct electronic
configuration of the magnesium ion?
This question is asking us to
identify the diagram showing the correct electronic configuration.
An electronic configuration shows
the distribution of electrons in energy levels of an atom or ion. The numbers written below the
energy levels indicate the amounts of electrons in those energy levels. The energy levels shown in each
diagram are levels K, L, M, and N. Each different energy level holds a
different maximum number of electrons. Level K can hold up to two
electrons. Level L can hold up to eight. Level M can hold up to 18. And level N can hold up to 32
electrons. Electrons tend to occupy the lowest
energy states, or in other words levels, as possible. So, electrons fill the lowest
energy levels first before occupying higher energy levels.
We are looking for the answer
choice that shows the electronic configuration of the magnesium ion. We are also told that magnesium has
an atomic number of 12, which means it has 12 protons. In a neutral magnesium atom, there
are also 12 electrons.
We are told that the magnesium ion
contains two fewer electrons than an atom of magnesium. The correct electronic
configuration will not contain 12 total electrons. Instead, to calculate the total
number of electrons in the ion, we must subtract two. The magnesium ion will then have 10
total electrons in its electronic configuration. We can see that the only diagram
with 10 total electrons is answer choice (B). The two electrons in the K level
and the eight in the L level is a total of 10 electrons.
Therefore, the energy level diagram
that shows the correct electronic configuration of the magnesium ion is answer
choice (B).
