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1. Halogen
2. Reactive non-metallic elements.
Element Chlorine Bromine Iodine
Proton number 17 35 53
Electronic
configuration2.8.7
[Ne] 3s3p2.8.18.7
[ Ar] 4s4p2.8.18.18.7
[Kr] 5s5p
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Bottle containingboth liquid and
gaseous bromine Solid
iodine
pieces
Copper
(II)
Fluoride
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Group 17, the nuclear charge &
the screening effect .
However, the in screening effect is the in nuclear charge,
causing a
in the effecetive nuclear charge.
Hence, the size of the atoms
down the group.
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Proton number Element No.ofelectrons/shell
9 fluorine2.7
17 Chlorine 2. 8. 7
35 Bromine2.8. 18. 7
53 Iodine2.8. 18. 18. 7
85 Astatine 2. 8. 18. 32. 18. 7
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Element Stateandcolour atroomtemperatureandpressure,colour
ofvapour whenheated
Fluorine pale yellow gas
Chlorine pale green gas
Bromine dark red liquid, readily gives off a brown vapour
Iodine dark (~black) crumbly solid, purple vapour
Astatine black solid, dark vapour - highly radioactive!
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The smaller the size the higher the
nuclear charge, causing the
attraction of the bond to bestronger.
G 17, the atomic size while the
effective nuclear charge .
Hence, the electronegativity .
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The first electron affinity refers to theenthalpy change for the
following process:
x(g) + e x(g)
o For example,a) Cl(g) + e Cl(g) H = -364KJ mol
b) I(g) + e I(g) H = -297KJ mol
o Atoms with smaller size and higher
effective nuclear charge will have higheraffinity for the added
electrons.
o Hence, the E.A. for the halogens thegroup.
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Have a simple molecular structure.
Consist of X molecules with strong covalentbond.
However, the intermolecular forces are theweakvander Waals
forces.
G17,the size / no. of electrons .
As a result, the B.P.,M.P. & E.V. as the
molecules become larger & the forces
become stronger.
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HalogenStandardAtomic
Weight (u)MeltingPoint (K) BoilingPoint (K)
Electronegativity(Pauling)
Fluorine 18.998 53.53 85.03 3.98
Chlorine 35.453 171.60 239.11 3.16
Bromine 79.904 265.80 332.00 2.96
Iodine 126.904 386.85 457.40 2.66
Astatine (210) 575 610 2.20
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halogen molecule structure model
Fluorine F2
Chlorine Cl2
Bromine Br 2
Iodine I2
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Bond Cl-Cl Br-Br I-I
Bond
energy/KJ mol
+244 +195 +152
DECREASES
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Acts as oxidising agents according to the
equation:
X(aq) + 2e 2X(aq)
Oxidising strength down the group due tothe in size & in the
E.A.
Chlorine candisplace( oxidise) bromide and
iodide ion from theiraq. solutions:
a) Cl(g) + 2Br(aq) Br(aq) +2Cl(aq)
b) Cl(g) + 2I(aq) I(aq) + 2Cl(aq)
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If the resulting solution is shaken with
tetrachromethane, the bromine liberatedwill colour the organic
layer reddish
brown, while iodine will colour it violet.
Bromine can only displace the iodide ions
from its aq. solutions.
Br(aq) + 2I(aq) I(aq) + 2Br(aq)
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Produce hydrogen halides (colourless
but form white fumes in moist air)
H(g) +X(g) 2HX(g)
Hydrogen: oxidation state of zero to
+1.
the group, the oxidising power,
hence the reactivity with hydrogen
also.
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a) Boiling point and melting point
o M.P. & B.P. In the order HCl
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G17, the H-X bonds get weakerdue to the
in the size.Hence, the stabilityof the HXdown the
group.
Bond H-Cl H-Br H-I
Bond
length
0.128 0.141 0.142
Bondenergy/
KJ mol
+430 +370 +300
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c) The hydrohalic acids
All the halogen halides dissolved inwater to produce acidic
solutions.
HX(g) + HO(l) HO(aq) + X(aq)
As the H-X bonds get weaker downthe group, the degree of
dissociation
in water .
Hence, the acid strength in the order
of
HCl
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Cl, Br & I react with cold & dilute sodium
hydroxide to form the halide & halate(I) ions.
CI(s) + 2NaOH(aq) NaCI(aq) +
NaOCI(aq)+ HO(l)
Br(s) + 2NaOH(aq) NaBr(aq) +NaOBr(aq)+ HO(l)
I(s) + 2NaOH(aq) NaI(aq) +NaOI(aq)+ HO(l)
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With the hot & conc. Sodium
hydroxide, the halogens react to
produce the halate(V) ions. For
example:
3Cl(g) + 6NaOH(aq) 5NaCl(aq) +NaCIO(aq) +3HO(I)
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Silver chloride is soluble in both dilute &
conc.ammonia.AgCl(s) + 2NH(aq) [Ag(NH)](aq)+Cl(aq)
Silver bromide is insoluble indilute
ammonia but is soluble in conc.ammonia.
AgBr(s) + 2NH(aq) [Ag(NH)](aq)+Br(aq)
Silver iodide is insoluble in both dilute &conc. aqueous
ammonia.
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Formed coloured precipitate of silver halide.
Examples: Ag(aq) + Cl(aq) AgCl(s)
white
: Ag(aq) + Br(aq) AgBr(s)
cream
: Ag(aq) + I(aq) AgI(s)
yellow
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white fumes of hydrogen halides are
liberated.
E.g : NaCl(s) + HSO(aq) NaHSO(aq) + HCl(g)
However, conc. sulphuric acid is also anoxidising agent, &
will further oxidise HBr &
HI to bromine( areddishbrown vapour) &iodine (a violet
vapuor) respectively .
2HBr(g) + HSO(aq) Br(g) + 2HO(l) + SO(g)
2HBr(g) + HSO(aq) Br(g) + 2HO(l) + SO(g)
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Manganese (IV) oxide is used to
oxidise HCl chlorine.
4NaCl(s)+
4HSO
(aq) + MnO
(aq) Cl(g) + MnCl(aq) 4NaHSO(aq)+ 2HO(l)
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Oxidationstate Example
-1 NaCl, HCl
0 Cl
+1 ClO, NaClO
+3 HClO, NaClO
+5 HClO, KClO
+7 KClO, ClO
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The oxo-acids of chlorine are:
HOCl,HClO, HClO, HClO
All the oxo-acids dissociate in water:
E.g: HOCl(aq) H(aq) + ClO(aq)
The acid strength depends on the
strength of the O-H bond in themolecule.
Oxygen is more electronegativity than
chlorine, hence the O-H bond in the
oxo-acids are weakened by the oxygenatoms which are bonded to
the chlorine
atoms
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The electrode process are:
The sodium produced at the cathodecombined with mercury to form
unreactivesodium amalgam.
The amalgam is directed into another steeltank where it reacts
with water to produce
sodium hydroxide and hydrogen gas.
2Na/Hg(l) + 2HO(l) 2NaOH(aq) + H(g) +2Hg(l)
Anode Cathode
2Cl(aq) Cl(g) + 2e 2Na(aq) + 2e 2Na(l)
Na(l) + Hg(l) Na/Hg(l)
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The brine solution enters the cell through
the anode compartment.
The chloride ion is discharged as chlorine gas
at the titanium anode. 2Cl(aq) Cl(g) + 2e
At the steel cathode, hydrogengas is
produced.
2H(aq) + 2e H(g)
Sodium hydroxide together with excess brine
is drainedout from the cell.
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1,2- dibromoethane is added to leaded petrol
to remove the lead oxide sticking to the
piston surface.
Silver bromide is used in the manufacture ofpjotographic
film.
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A solution of iodine in ethanol is a
disinfectant.
Silver bromide is used in photpgraphic film
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1. HCl, HBr and HI dissolves in water to form
acidic solutions.
i) Write a balanced equation for the
reactions between hydrogen chloride andwater.
ii) Arrange the three aqueous hydrogen
halides in the order of increasing acid
strength. Explain you answer.
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2. Describe the reactions between chlorine,
bromine and iodine with hydrogen.
