7 electrons in their outer shell, they need
one more for a full outermost shell and
they are really reactive
At room temperature:
Chlorine is fairly reactive and
poisonous, it is a green gas which
is very dense
Bromine is also a dense
halogen; it is an orange
liquid which is poisonous
Iodine is dark grey, and is a crystalline solid
Halogens react with most metals to form salts
called metal halides
Halogens also react with oxygen to
form Hydrogen Halides
e.g. chlorine reacts with
hydrogen to form hydrogen
chloride gas
then the hydrogen
chloride gas can be
dissolved in water
to form hydrochloric
acid
They are soluble in water and
form acidic solutions
Group 1 form alkaline
solutions, Group 7 form
acidic solutions
The closer to the top in group
7, the more reactive and the
further down the least reactive.
This is because near the top
the electrons are closer to the
nucleus. This means that the
force is greater and attracts
extra electrons more strongly
When halides dissolve it
water, the electrons are
more free to react
If a more reactive
halogen reacts with
a less reactive one
in a solution then
the more reactive
will displace the less
reactive halogen.
E.g. Lithium would
displace Potassium