Download chlorine bromine iodine Halogen Reaction with Iron wool

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Halogens (6 min)
https://www.youtube.com/watch?v=yW_C10
cEzMk
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State at room temperature
• Chlorine is a yellow – green gas
• Bromine is a red - brown liquid which easily
evaporates to give an orange – brown vapour
• Iodine is a grey – black solid which sublimes to
give a violet vapour
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What are the halogens?
The halogens are the elements in Group 7 of the
periodic table.
The name halogen comes from the Greek
words for salt-making.
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Physical properties of halogens
What is the trend here for boiling and melting points?
What is the trend for color?
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Trends in boiling point
Halogen molecules increase in number of electrons down the
group. This leads to greater van der Waals forces between
molecules, increasing the energy needed to separate the
molecules and therefore higher melting and boiling points.
van der
Waals forces
fluorine
atomic radius = 42 × 10-12 m
boiling point = -118 °C
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iodine
atomic radius = 115 × 10-12 m
boiling point = 184 °C
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Hydrogen halides
Predict HF
boiling point
Why are you wrong?
Hydrogen halide
Boiling point (°C)
HF
20
HCl
-85
HBr
-67
HI
-35
Hydrogen fluoride has an
unexpectedly high boiling point
compared to the other
hydrogen halides. This is due to
hydrogen bonding between the
H–F molecules.
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Trends in electronegativity
Electronegativity, or ability to attract electrons, what is the trend?
Answer:
decreases down the group
Why?
Although there is an increased nuclear charge there no
significant effect from all these protons because there are more
electron shells and more shielding. Iodine atoms therefore attract
electrons density less strongly than fluorine.
What does this suggest about halogen reactivity?
fluorine
atomic radius = 42 × 10-12 m
electronegativity = 4.0
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iodine
atomic radius = 115 × 10-12 m
electronegativity = 2.5
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Astatine
The name astatine comes from the Greek word for unstable.
It is estimated that only 30 grams of astatine exist
on Earth at any one time. This is because it is
radioactive, and its most stable isotope (210At)
has a half-life of only 8 hours.
It was first made artificially in 1940, by bombarding 209Bi with aradiation. Predict the properties of astatine?
 Colour?
Answer: Very Dark, perhaps black (presumed) Why presumed?
 State at room temperature?
Answer: Solid
 Electronegativity?
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Answer: Low, perhaps 2.2
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Quiz
1. Features included in group VII elements are
A) non-metals B) diatomic molecules C)single covalent bond D) all of them
ANS: D
2. Forces between diatomic halogens are
A)Van der Waal's forces B) dipole-dipole forces C) electrovalent forces D) Hydrogen bond
ANS: A
3. Volatility of Halogens indicates their
A)Relative inertness B) ease of evaporation C) density D) All of Above
Answer B
4. Halogen that is least volatile is
A)F2
B) Cl2
C) Br2
D) I2
Answer D
5.) Color of Iodine (I2) is
A)White B) yellow C) purple (vapors) D) red
Answer C
6.) Hydroiodic acid is one of the 6 strong acids, so why is hydrofluoric acid so much
higher than HI in boiling and melting points?
A)HF has less electrons B) HI nucleus is more shielded
C) Hydrogen Bonding
ANSWER C
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Reactions with hydrogen
The halogens react with H2 to product hydrogen halides.
Cl2(g) + H2(g)  2HCl(g)
FAST

Chlorine and hydrogen explode in bright sunlight but
react slowly in the dark.

Bromine and hydrogen react slowly on heating with
a platinum catalyst.
Br2(g) + H2(g)  2HBr(g)

SLOW
VERY POOR: Iodine combines partially and very
slowly with hydrogen, even on heating.
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Reactivity with Iron
Halogen Reaction with iron wool
Fluorine
Reacts with almost anything instantly. Very few
scientists handle fluorine because it is so
dangerous.
Chlorine
Reacts with heated iron wool very quickly.
Bromine
Has to be warmed and the iron wool heated. The
reaction is faster.
Iodine
Has to be heated strongly. The reaction is slow
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What is the reactivity of the halogens?
The reactions of the halogens with iron and hydrogen show
that their reactivity decreases down the group.
Halogen
Reaction with Iron wool
A Metal
chlorine Iron wool burns brightly.
Reaction with
hydrogen
Explodes in
sunlight, reacts
slowly in the dark.
bromine Iron wool glows but less
Reacts slowly on
brightly than with chlorine. heating with catalyst.
iodine
Iron wool has a very
slight glow.
Reacts partially
and very slowly.
How do you think fluorine and astatine would react with
iron wool and hydrogen?
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Halogen Reactivity
What generalization can you make about halogen reactivity?
Halogens decrease down the group: At < I < Br < Cl < F
What feature of halogen molecules accounts for the trend above?
Atomic radius increases in size down the group. Although the
nuclear charge increases, the shielding effect of the inner
electrons blocks its pull.
This lessens the attraction for valence electrons of other atoms,
decreasing reactivity.
This decrease also occurs because electronegativity decreases
down a group; therefore, there is less electron "pulling.“ ability.
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Halide
ion
Action of AgNO3(aq)
Action of dilute NH3(aq)
Action of conc. NH3(aq)
F–(aq)
Cl–(aq)
Br–(aq)
I–(aq)
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Halide
ion
Action of AgNO3(aq)
F–(aq)
No precipitate
Action of dilute NH3(aq)
Action of conc. NH3(aq)
Cl–(aq)
Br–(aq)
I–(aq)
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Halide
ion
Action of AgNO3(aq)
F–(aq)
No precipitate
Cl–(aq)
Ag+(aq) + Cl–(aq) → AgCl(s)
white ppt
Action of dilute NH3(aq)
Action of conc. NH3(aq)
Br–(aq)
I–(aq)
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Halide
ion
Action of AgNO3(aq)
F–(aq)
No precipitate
Action of dilute NH3(aq)
Action of conc. NH3(aq)
Soluble
Cl–(aq)
Ag+(aq) + Cl–(aq) → AgCl(s)
white ppt
AgCl(s) + 2 NH3(aq) →
[Ag(NH3)2]+(aq) + Cl–(aq)
Br–(aq)
I–(aq)
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Halide
ion
Action of AgNO3(aq)
F–(aq)
No precipitate
Cl–(aq)
Ag+(aq) + Cl–(aq) → AgCl(s)
white ppt
Action of dilute NH3(aq)
Action of conc. NH3(aq)
Soluble
Soluble
AgCl(s) + 2 NH3(aq) →
[Ag(NH3)2]+(aq) + Cl–(aq)
AgCl(s) + 2 NH3(aq) →
[Ag(NH3)2]+(aq) + Cl–(aq)
Br–(aq)
I–(aq)
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Halide
ion
Action of AgNO3(aq)
F–(aq)
No precipitate
Cl–(aq)
Br–(aq)
Ag+(aq)
+
Cl–(aq)
→ AgCl(s)
white ppt
Action of dilute NH3(aq)
Action of conc. NH3(aq)
Soluble
Soluble
AgCl(s) + 2 NH3(aq) →
[Ag(NH3)2]+(aq) + Cl–(aq)
AgCl(s) + 2 NH3(aq) →
[Ag(NH3)2]+(aq) + Cl–(aq)
Ag+(aq) + Br–(aq) → AgBr(s)
cream ppt
I–(aq)
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Halide
ion
Action of AgNO3(aq)
F–(aq)
No precipitate
Cl–(aq)
Br–(aq)
Ag+(aq)
+
Cl–(aq)
→ AgCl(s)
white ppt
Ag+(aq) + Br–(aq) → AgBr(s)
cream ppt
Action of dilute NH3(aq)
Action of conc. NH3(aq)
Soluble
Soluble
AgCl(s) + 2 NH3(aq) →
[Ag(NH3)2]+(aq) + Cl–(aq)
AgCl(s) + 2 NH3(aq) →
[Ag(NH3)2]+(aq) + Cl–(aq)
Insoluble
I–(aq)
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Halide
ion
Action of AgNO3(aq)
F–(aq)
No precipitate
Cl–(aq)
Br–(aq)
Ag+(aq)
Ag+(aq)
+
Cl–(aq)
+
Br–(aq)
→ AgCl(s)
white ppt
→ AgBr(s)
cream ppt
Action of dilute NH3(aq)
Action of conc. NH3(aq)
Soluble
Soluble
AgCl(s) + 2 NH3(aq) →
[Ag(NH3)2]+(aq) + Cl–(aq)
AgCl(s) + 2 NH3(aq) →
[Ag(NH3)2]+(aq) + Cl–(aq)
Soluble
Insoluble
AgBr(s) + 2 NH3(aq) →
[Ag(NH3)2]+(aq) + Br–(aq)
I–(aq)
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Halide
ion
Action of AgNO3(aq)
F–(aq)
No precipitate
Cl–(aq)
Br–(aq)
Ag+(aq)
Ag+(aq)
I–(aq)
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+
Cl–(aq)
+
Br–(aq)
→ AgCl(s)
white ppt
→ AgBr(s)
cream ppt
Action of dilute NH3(aq)
Action of conc. NH3(aq)
Soluble
Soluble
AgCl(s) + 2 NH3(aq) →
[Ag(NH3)2]+(aq) + Cl–(aq)
AgCl(s) + 2 NH3(aq) →
[Ag(NH3)2]+(aq) + Cl–(aq)
Soluble
Insoluble
AgBr(s) + 2 NH3(aq) →
[Ag(NH3)2]+(aq) + Br–(aq)
Ag+(aq) + I–(aq) → AgI(s)
yellow ppt
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Halide
ion
Action of AgNO3(aq)
F–(aq)
No precipitate
Cl–(aq)
Br–(aq)
Ag+(aq)
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+
Br–(aq)
→ AgCl(s)
white ppt
Action of conc. NH3(aq)
Soluble
Soluble
AgCl(s) + 2 NH3(aq) →
[Ag(NH3)2]+(aq) + Cl–(aq)
AgCl(s) + 2 NH3(aq) →
[Ag(NH3)2]+(aq) + Cl–(aq)
Soluble
→ AgBr(s)
cream ppt
Insoluble
Ag+(aq) + I–(aq) → AgI(s)
yellow ppt
Insoluble
Ag+(aq)
I–(aq)
+
Cl–(aq)
Action of dilute NH3(aq)
AgBr(s) + 2 NH3(aq) →
[Ag(NH3)2]+(aq) + Br–(aq)
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Halide
ion
Action of AgNO3(aq)
F–(aq)
No precipitate
ALWAYS Soluble
Cl–(aq)
Br–(aq)
I–(aq)
Ag+(aq)
Ag+(aq)
+
Cl–(aq)
+
Br–(aq)
→ AgCl(s)
white ppt
→ AgBr(s)
cream ppt
Ag+(aq) + I–(aq) → AgI(s)
yellow ppt
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Action of dilute NH3(aq)
nothing to dissolve
Action of conc. NH3(aq)
nothing to dissolve
Soluble
Soluble
AgCl(s) + 2 NH3(aq) →
[Ag(NH3)2]+(aq) + Cl–(aq)
AgCl(s) + 2 NH3(aq) →
[Ag(NH3)2]+(aq) + Cl–(aq)
Soluble
Insoluble
AgBr(s) + 2 NH3(aq) →
[Ag(NH3)2]+(aq) + Br–(aq)
Insoluble
Insoluble
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Reactions with halide ions
What is the redox pattern with halogens and
the Halide ions?
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Cl2(aq)
Br2(aq)
I2(aq)
Cl–(aq)
Br–(aq)
I–(aq)
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Cl2(aq)
Cl–(aq)
Br2(aq)
I2(aq)
Stays yellow solution
(no reaction)
Br–(aq)
I–(aq)
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Cl2(aq)
Cl–(aq)
Br2(aq)
I2(aq)
Stays yellow solution
(no reaction)
Stays brown solution
(no reaction)
Br–(aq)
I–(aq)
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Cl2(aq)
Cl–(aq)
Br–(aq)
Br2(aq)
I2(aq)
Stays yellow solution
(no reaction)
Stays brown solution
(no reaction)
Yellow solution forms
(Br2 forms)
Cl2 + 2 Br-→ 2 Cl- + Br2
I–(aq)
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Cl2(aq)
Cl–(aq)
Br–(aq)
Yellow solution forms
(Br2 forms)
Cl2 + 2 Br-→ 2 Cl- + Br2
Br2(aq)
I2(aq)
Stays yellow solution
(no reaction)
Stays brown solution
(no reaction)
Stays brown solution
(no reaction)
I–(aq)
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Cl2(aq)
Cl–(aq)
Br–(aq)
Yellow solution forms
(Br2 forms)
Cl2 + 2 Br-→ 2 Cl- + Br2
I–(aq)
Br2(aq)
I2(aq)
Stays yellow solution
(no reaction)
Stays brown solution
(no reaction)
Stays brown solution
(no reaction)
Brown solution forms
(I2 forms)
Cl2 + 2 I- → 2 Cl- + I2
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Cl2(aq)
Cl–(aq)
Br–(aq)
Br2(aq)
I2(aq)
Stays yellow solution
(no reaction)
Stays brown solution
(no reaction)
Yellow solution forms
(Br2 forms)
Stays brown solution
(no reaction)
Cl2 + 2 Br-→ 2 Cl- + Br2
I–(aq)
Brown solution forms
(I2 forms)
Brown solution forms
(I2 forms)
Cl2 + 2 I- → 2 Cl- + I2
Br2 + 2 I- → 2 Br- + I2
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Oxidising power trend: Cl2 > Br2 > I2
When a halogen acts as an oxidising agent, it gains
electrons (taken from the oxidised species).
X + 2 e- → 2 XC
l
Br
I
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2
Down the group it becomes harder to
gain an electron because:
atoms are larger & there is more
shielding (due to extra electron shell)
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Halogen displacement reactions
Halogen displacement reactions are redox reactions.
Cl2 + 2KBr  2KCl + Br2
To look at the transfer of electrons in this reaction, the
following two half equations can be written:
Cl2 + 2e-  2Cl-
2Br-  Br2 + 2e-
What has been oxidized and what has been reduced?

Chlorine has gained electrons, so it is reduced to Cl- ions.

Bromide ions have lost electrons, so they have been
oxidized to bromine.
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In displacement reactions between
halogens and halides, the halogen
acts as an oxidizing agent.
This means that the halogen:

gains electrons

is reduced to form the halide ion.
What is the order of oxidizing
ability of the halogens?
increasing oxidizing ability
Oxidizing ability of halogens
fluorine
chlorine
bromine
iodine
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USES OF HALOGENS
Fuse School Uses of Halogens (4 Min)
https://www.youtube.com/watch?v=wXingx2
RokI
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Manufacture of Bleach
2NaOH(aq) + Cl  NaOCl (aq) + NaCl (aq) + H O (l)
Omit Na+ spectator ion and you see a
Disproportionation reaction, which is…?
Answer: Reactant is both oxidized and reduced.
OH - + Cl2(g)  OCl- + Cl2
2
4OH- + 2H2O + Cl2  2OCl - + 4H+ + 2e- + 4OH2e- + Cl2
 2Cl 4OH- + 2Cl2
 2Cl - + 2OCl- + 2H2O DIVIDE all by 2
2OH- + Cl2
 Cl - + OCl- + H2O
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Uses of Halogens
• Chlorine is used to purify water in swimming pools
etc as it kills bacteria.
• Chlorine is also used as bleach.
• Iodine is used as an antiseptic on cuts and grazes.
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Reaction of chlorine with water
Chlorine is used to purify water supplies
because it is toxic to bacteria, some of
which can cause disease. Adding it to
water supplies is therefore beneficial for
the population.
However, chlorine is also toxic to humans,
so there are risks associated with gas leaks
during the chlorination process. There is
also a risk of the formation of chlorinated
hydrocarbons, which are also toxic.
Chlorination of drinking water raises questions about individual
freedom because it makes it difficult for individuals to opt out.
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Uses of halides in photography
Silver halides are used in photography.
Photographic film coated with a silver halide is exposed to
light, causing the halide to decompose to form silver. This
appears as a black precipitate on the photographic film.
Ag+ + e-  Ag
light
covering
paper
coated in
silver halide
silver
precipitate
white paper
under the
cover
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Halides
When halogens react with metals, they form compounds
called halides. Many naturally-occurring halides have
industrial, household and medical applications.
Halide
Formula Uses
cesium chloride
CsCl
Extraction and
separation of DNA
sodium
hexafluoroaluminate
NaAlF6
Electrolysis of
aluminium oxide
titanium(IV) chloride
TiCl4
Extraction of titanium
lithium iodide
LiI
Electrolyte in batteries
potassium bromide
KBr
Epilepsy treatment in
animals
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Terminology
• hydrogen bonding – A special example of a permanent dipole–dipole
intermolecular force that occurs when hydrogen is bonded to nitrogen,
oxygen or fluorine. An extremely strong dipole-dipole interaction
• oxidation state – The charge a particular atom in a compound would
have if the compound consisted entirely of separate ions.
• oxidation – The process during which an atom, molecule or ion loses
one or more electrons and increases in oxidation state.
• oxidizing agent – A species that accepts electrons, thus oxidizing
another species while it is itself reduced.
• redox – Short for reduction / oxidation. A chemical reaction in which
the reacting species have their oxidation states changed.
• reduction – The process in which an atom, molecule or ion gains one
or more electrons and decreases in oxidation state.
• reducing agent – A species that donates electrons, thus reducing
another species while it is itself oxidized.
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Terminology
• displacement reaction – A reaction in which an element is displaced out
of a compound by a more reactive element; for example, bromine
displaces iodine from potassium iodide: Br2 + 2KI  2KBr + I2.
• disproportionation – A reaction in which the same element is both
oxidized and reduced; for example, chlorine in: Cl2 + H2O > HCl + HOCl.
• electronegativity – The power of an atom to withdraw electron density
and attract the pair of bonding electrons in a covalent bond.
• half equation – An equation describing either the oxidation or reduction in
a redox reaction in terms of electron loss and electron gain. For example,
Cl2 + 2e-  2Cl- shows the reduction of chlorine to chloride ions.
• halide – A salt formed by the reaction of a halogen with a metal.
• halide ion – A negative ion formed by the addition of an electron to an
atom of a halogen.
• halogen – A group 7 element.
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