the halogens are the elements in group 7
of the periodic table
they are fluorine chlorine bromine
iodine and astatine
in this lesson we will learn about the
halogens and their key reactions the
displacement reactions reaction with
metals and reaction with hydrogen
halogens in their elemental form are
toxic though their compounds have many
real-life applications
the halogens all have seven electrons in
their valence shell and can accept one
electron to form an ion with a -1 charge
moving down the group atomic radii
increases by one electron shell
as a consequence melting points and
boiling points and their density also
increase
to illustrate this
fluorine and chlorine are gases bromine
is a liquid and iodine and astatine are
solids
fluorine is a very pale green gas
chlorine is a greenish yellow gas
bromine is a reddish brown liquid
iodine is a gray solid that sublimes to
a purple vapor
astatine is the black solid and
radioactive
moving down the group the reactivity of
the halogens decreases
so a selected halogen is always more
reactive than the halogens below it
a more reactive halogen will always
displace a less reactive halogen in a
compound we will demonstrate these
displacement reactions
using aqueous solutions of potassium
chloride potassium bromide and potassium
iodide
note that these are all halogen
containing compounds
when we add chlorine water to an aqueous
solution of potassium chloride no
reaction happens
since chlorine is more reactive than
bromine
chlorine will displace bromine in
potassium bromide producing potassium
chloride and liberating bromine
the resulting solution is reddish brown
due to the presence of bromine
a similar observation occurs when
chlorine water is added to an aqueous
solution of potassium iodide
since chlorine is more reactive than
iodine a displacement reaction will
occur to liberate iodine according to
the reaction below
a dark brown solution is produced due to
the presence of iodine
let's predict what happens when bromine
water is added to the same three aqueous
solutions
please pause the lesson to think about
this and resume once you are done
when we add bromine water to aqueous
potassium chloride this causes the
solution to turn reddish brown but no
displacement reaction occurs as bromine
is less reactive than chlorine
no reaction occurs when bromine water is
added to aqueous potassium bromide
as bromine is more reactive than iodine
it will displace and liberate iodine in
potassium iodide
therefore a dark brown solution is
produced due to the presence of iodine
if we added iodine to the same three
aqueous solutions no displacement
reactions occur as iodine is less
reactive than both chlorine and bromine
halogens can react with certain metals
to form metal halides
a very common metal halide is sodium
chloride or regular table salt
sodium chloride is extracted from the
sea or from salt mines
sodium chloride can be produced from the
reaction of heated sodium metal with
chlorine gas
since it is a highly exothermic reaction
it is not recommended that this be done
in a laboratory
halogens can react with hydrogen gas to
produce the corresponding hydrogen
halide
most of these reactions are also highly
exothermic
as an example chlorine gas and hydrogen
gas can react to form hydrogen chloride
in summary the halogens are the group
seven elements
their displacement reactions involve a
more reactive halogen displacing a less
reactive halogen in a compound
halogens
can also react with metals to produce
the corresponding metal halides and can
react with hydrogen to produce hydrogen
halides
you