Video Transcript
Typically, how might an element
with three electrons in its outermost energy level behave in a reaction?
We are asked about an element which
has three electrons in its outermost energy level. We need to describe how such an
element would behave in a chemical reaction. Let’s start by drawing a diagram to
show the electron placement or electronic configuration of an atom of this
element. We know atoms have a nucleus with
protons and neutrons. In this case, we do not know how
many of each subatomic particle there are in the nucleus, nor do we know how many
electrons an atom of this element has or how many electron shells are filled. So, for simplicity, let us draw
just three energy levels.
We do, however, know that an atom
has an equal number of protons and electrons, making it neutral. And we know that there are three
electrons in its outer shell. We know that all inner shells are
full. The full electronic configuration
of this atom is shown here. But remember, there are other
possible electronic configurations if we add more inner shells. Again, we do not know how many
inner shells there are in this atom. We have just chosen to work with
two inner shells.
Now, metal atoms tend to have one,
two, or three electrons in their outer shell, and nonmetal atoms tend to have five,
six, or seven electrons in their outer shell. Atoms that have less than eight
electrons in their outer shell are unstable. Helium, however, is stable even
though it has less than eight electrons, since its outer shell is full with two
electrons. We can deduce that the element in
question must be a metal since we are told it has three outer electrons. Except for the noble gas atoms,
which tend to be unreactive, atoms tend to lose or gain electrons in a chemical
reaction and usually end up with eight electrons in their outer shell. When there are eight electrons in
the outer shell, an atom is stable, like the noble gases.
In this question, we have a metal
atom. Metal atoms tend to lose all their
outer electrons in chemical reactions and end up with the electronic configuration
of a noble gas. Nonmetal atoms do the opposite;
they gain electrons. So, we know this metal atom will
lose outer electrons. But how many electrons will an atom
of this element lose? We said they will lose all their
outer electrons. So, it will lose all three of its
outer electrons.
Now, the number of protons is no
longer equal to the number of electrons, but there are three more protons than
electrons. A positively charged particle will
form, with a plus three charge. We call this particle an ion. An ion is a particle with an
unequal number of protons and electrons. So, how does an element with three
electrons in its outer energy level behave? The answer is it loses its three
electrons and changes to a positive ion.