Video Transcript
As the atomic number of the halogen
increases, what happens to its atomic radius and reactivity?
We are asked about two properties,
atomic radius and reactivity, of the halogens. Let’s have a closer look at the
halogen group. The halogens include the elements
fluorine, chlorine, bromine, iodine, and astatine. The halogens can be found in group
17 of the periodic table. The group number is the vertical
column on the periodic table. Each of the halogens is in a
different period on the periodic table, which is the horizontal row.
Elements in the same group number
all have the same number of outer-shell electrons. Elements in the same period have
the same number of energy levels that contain electrons. So as we go down the halogen group,
each halogen has one more energy level than the last. With more energy levels, the atomic
radius increases. As we go down the group, the atomic
number also increases. Therefore, the atomic radius
increases with atomic number.
Let’s have a closer look at the
reactivity of the halogens. We will use fluorine to see how
halogens generally react. With seven outer-shell electrons,
halogens often react by gaining one new electron. When this occurs, a halide ion is
formed. A halide ion is formed when a
single halogen atom has gained one electron to become an anion with a one minus net
charge. Generally, it is easier for
halogens to gain one electron with a smaller atomic radius. This occurs due to reasons that are
outside the scope of this video. Therefore, reactivity is greater
for halogens with a smaller atomic radius. Reactivity thus decreases with
increasing atomic number.
So as the atomic number of the
halogen increases, the atomic size increases and the reactivity decreases.
