Video Transcript
What happens to the attractive
forces between the molecules and density of halogens as you go down group 17 of the
periodic table?
This question is asking us about
the group on the periodic table called the halogens. The question tells us that they are
in group 17, which is the 17th vertical column of the periodic table. Let’s have a closer look at the
elements in this group.
These five elements make up the
halogen group. They are fluorine, chlorine,
bromine, iodine, and astatine. As we saw, these are the elements
of group 17. They are all nonmetals. They are also all diatomic. This means their molecules are made
up of two atoms bonded together. This is why we will see their
chemical formulas written with their chemical symbols and a subscript of two to
represent that they are diatomic.
The question asks us about two
properties and how they change going down the halogen group. As we go down the group, each
halogen is in a different horizontal row on the periodic table called a period. Let’s have a look at how these
elements’ states of matter change to further investigate their density and
attractive forces.
We’ll start at the top of the
group, with fluorine. Fluorine is a pale-yellow gas at
room temperature. As a gas, its molecules have a lot
of space between them. Since the molecules are far apart
and not packed closely together, fluorine has a low density.
Next, we’ll look at chlorine. Chlorine is a yellow to green
gas. As a gas, its density is relatively
low. But chlorine is more dense than
fluorine.
The next halogen, bromine, exists
at room temperature as a dark-red liquid. Bromine also gives off red-orange
vapors. Bromine is more dense than the
previous two halogens as its molecules are more closely arranged together.
Let’s look at iodine. Iodine is a black or gray
crystalline solid at room temperature. And at around 114 degrees Celsius,
it gives off purple vapors. As a solid, iodine’s particles are
packed very closely and neatly together, making it very dense.
Finally, astatine is the rarest and
most radioactive halogen. And since its isotopes decay so
quickly, we will not consider it in our discussion.
As we can see, the halogens become
more dense as we go down the group. But what happens to the attractive
forces between their molecules?
Fluorine and chlorine are both
gases, bromine is a liquid, and iodine is a solid. As gases, the molecules of fluorine
and chlorine must be far apart and, thus, are not strongly attracted to each
other. Bromine molecules are in the liquid
state and, thus, are closer together and more strongly attracted to each other. Iodine, as a solid, has molecules
that are very strongly attracted and packed closely together. Therefore, the attractive forces
between molecules increases down the group as well.
So, as we go down the halogens, or
group 17 of the periodic table, the attractive forces increase and the halogen
becomes more dense.
