Video Transcript
An atom has three energy levels
with electrons and eight electrons in energy level M. What is the electronic
configuration of this atom?
We need some space to think about
this question before selecting the answer. So let’s remove the answer options
for now.
Atoms are made from a central
nucleus, which contains positively charged protons and neutral neutrons. Negatively charged electrons are
arranged outside the nucleus in different energy levels, which are also called
shells. Electrons fill up the energy level
closest to the nucleus first before any are placed into the next energy level. Then, if an atom has more
electrons, these electrons go into the second energy level and will fill this energy
level before any are placed into the third energy level. Then, if there are still more
electrons, they go into the third energy level.
The energy level closest to the
nucleus is lowest in energy. We call this first energy level
energy level K. Energy level K can hold up to a
maximum of two electrons. The second energy level is called
energy level L, and it can hold up to a maximum of eight electrons. Then, the third energy level is
called energy level M, and this can hold up to a maximum of 18 electrons. There are more energy levels, but
let’s just look at these three, since these are the energy levels given in the
answer options.
Now that we know the maximum number
of electrons each shell or energy level can hold, let us remove these electrons and
fill in the number of electrons told to us in the question. The question mentions that an atom
has three energy levels with electrons. Since we know that electrons fill
the lowest energy level first, then the second energy level, then the third, and so
on, we can deduce that the three energy levels which contain electrons must be the
first three energy levels. These energy levels are energy
levels K, L, and M.
We are also told that the atom has
eight electrons in energy level M. So we can write eight in the M
energy level. Since we are told there are
electrons in energy level M, this must mean that energy levels K and L are both
full. So we can deduce that there are two
electrons in energy level K. And we can deduce that there must
be eight electrons in energy level L. We already filled in the eight
electrons for energy level M. Notice, this energy level is not
full. Remember, it can hold up to 18
electrons.
Now, we are asked for the
electronic configuration of the atom in question. Electronic configuration is the way
in which electrons are arranged in an atom, or we could say it is the distribution
of electrons in energy levels. We can see from the diagram that
the electronic configuration for this atom is two electrons in energy level K, eight
electrons in energy level L, and eight electrons in energy level M.
Now, let’s bring back our answer
options to see which one matches this electronic configuration. If we examine these diagrams, we
can see that only answer (A) has the same electronic configuration as the one we
deduced. So, we can conclude that the
correct electronic configuration for this atom is answer (A).
