Video Transcript
Although some elements are
exceptions, there is a link between the group number of an element and its
valence. By looking at the following table,
what is the value of 𝑋 most likely to be?
The valence of an element is the
number of electrons that an atom gains, loses, or shares when forming a bond during
a chemical reaction. Atoms tend to gain or lose
electrons like this so they can attain a stable electronic configuration. An electronic configuration is
stable if the K-shell is filled with two electrons and other shells are filled with
eight electrons.
For example, let’s figure out the
valence of this atom with the electronic configuration 2,7. The L-shell in this atom has seven
electrons, meaning it is one electron away from being full. So this atom will likely gain one
electron to fill that L-shell. Once the atom gains one electron,
it has attained a stable electronic configuration. Since this atom tends to gain one
electron, it has a valence of one.
Let’s look at another example, an
atom with the electronic configuration 2,2. There are two ways this atom could
attain a stable electronic configuration. If the atom gains six electrons,
the L-shell will be filled. The atom could also lose two
electrons, leaving a full K-shell. However, it’s more likely that the
atom will gain or lose a smaller number of electrons than a large amount of
electrons. So this atom has a valence of two,
since it will tend to lose two electrons.
Now, this question suggests there
is a link between the group number and the valence. Let’s use this particular atom as
an example to explore this connection. This atom has four electrons,
meaning that it must be an atom of beryllium, an element found in group two of the
periodic table. Elements in group two of the
periodic table, like beryllium, all have two electrons in the outer shell. So atoms of elements in group two
all have a tendency to lose the two electrons in the outer shell to attain a stable
electronic configuration. This means that elements in group
two have a valence of two, as the table suggests.
This question asks us what the
value of 𝑋 is most likely to be. 𝑋 is the value in the table for
the valence of elements in group five. Let’s look at an example of a group
five element, nitrogen. Atoms of nitrogen have an
electronic configuration of 2,5. With five electrons in the outer
shell, atoms of nitrogen have a tendency to gain three electrons to fill the
L-shell. As atoms of nitrogen have a
tendency to gain three electrons, nitrogen has a valence of three.
Elements in group five have a
similar electronic configuration, with five electrons in the outer shell. Because of this, elements in group
five tend to have a valence of three, though there are exceptions in this group. As 𝑋 corresponds to the valence of
group five elements, the most likely value of 𝑋 is three.
