Group 7 Elements
Physical & chemical data
Fluorine
Chlorine
Bromine
Iodine
Astatine
Selected Properties of the Group 7 Halogens
Symbol Atomic
Electron
and
Number arrangement
Name
State and colour at room temperature,
colour of vapour when heated
Melting
point
Boiling atom
point radius
nm
F
Fluorine
9
2.7
pale yellow gas
-220oC, 53K
-188oC
85K
0.072
Cl
Chlorine
17
2.8.7
green gas
-102oC,
173K
-34oC,
239K
0.099
Br
Bromine
35
2.8.18.7
dark red liquid, brown vapour
-7oC, 266K
59oC,
332K
0.114
I Iodine
53
2.8.18.18.7
dark crumbly solid, purple vapour
114oC, 387K
184oC,
457K
0.133
At
Astatine
85
2.8.18.32.18.7
302oC 575K
380oC
653K
0.140
black solid, dark vapour
electron configuration
fluorine
chlorine
bromine
iodine
astatine
F
Cl
Br
I
At
[He]2s22p5
[Ne]3s23p5
[Ar]3d104s2 4p5
[Kr]4d105s2 5p5
[Xe]4f14 5d106s2 6p5
Occurrence and Extraction
The halogens are too reactive to occur free in nature. Fluorine is mined as fluorspar, calcium
fluoride and cryolite. It is extracted by electrolysis as no oxidant will oxidise fluorides to fluorine.
Chlorine is also found in minerals such as rock-salt, and huge quantities of chloride ions occur in
seawater, inland lakes and subterranean brine wells. It is obtained by the electrolysis of molten
sodium chloride or brine. Bromine is also found as the bromide ion in seawater, and in larger
quantities in brine wells, from which it is extracted. Iodine is mined as sodium iodate(V), NaIO 3,
which is present in Chile saltpetre. It is obtained by reaction with sodium hydrogensulfite.
Electron Affinity (M-M-)kJ mol-1
F
Cl
Br
I
-333
-348
-324
-295
Ionisation Energies/kJ mol-1
F
Cl
Br
I
1st
1681
1251.1
1139.9
1008.4
2nd
3374
2297
2104
1845.9
3rd
6050
3826
3500
3200
4th
8408
5158
4560
4100
The Halogens in their Elemental Form
Fluorine (F2), a highly toxic, colorless gas, is the most reactive element known
so reactive that
asbestos, water, and silicon burst into flame in its presence. It is so reactive it even forms compounds with
Kr, Xe, and Rn, elements that were once thought to be inert. Fluorine is such a powerful oxidizing agent that
it can coax other elements into unusually high oxidation numbers, as in AgF2, PtF6, and IF7.
Fluorine is so reactive that it is difficult to find a container in which it can be stored. F2 attacks both glass and
quartz, for example, and causes most metals to burst into flame. Fluorine is handled in equipment built out
of certain alloys of copper and nickel. It still reacts with these alloys, but it forms a layer of a fluoride on the
surface that protects the metal from further reaction.
Fluorine is used in the manufacture of Teflon
or poly(tetrafluoroethylene), (C2F4)n
which is used for
everything from linings for pots and pans to gaskets that are inert to chemical reactions. Large amounts of
fluorine are also consumed each year to make the freons (such as CCl2F2) used in refrigerators.
Chlorine (Cl2) is a highly toxic gas with a pale yellow-green color. Chlorine is a very strong oxidizing
agent, which is used commercially as a bleaching agent and as a disinfectant. It is strong enough to oxidize
the dyes that give wood pulp its yellow or brown color, for example, thereby bleaching out this color, and
strong enough to destroy bacteria and thereby act as a germicide. Large quantities of chlorine are used each
year to make solvents such as carbon tetrachloride (CCl4), chloroform (CHCl3), dichloroethylene (C2H2Cl2),
and trichloroethylene (C2HCl3).
Bromine
(Br2) is a reddish-orange liquid with an unpleasant, choking odor. The name of the element, in
fact, comes from the Greek stem bromos, "stench." Bromine is used to prepare flame retardants, fireextinguishing agents, sedatives, antiknock agents for gasoline, and insecticides.
Iodine is an intensely colored solid with an almost metallic luster. This solid is relatively volatile, and it
sublimes when heated to form a violet-colored gas. Iodine has been used for many years as a disinfectant in
"tincture of iodine." Iodine compounds are used as catalysts, drugs, and dyes. Silver iodide (AgI) plays an
important role in the photographic process and in attempts to make rain by seeding clouds. Iodide is also
added to salt to protect against goiter, an iodine deficiency disease characterized by a swelling of the thyroid
gland.
Some of the chemical and physical properties of the halogens are summarized in the table below. There is a
regular increase in many of the properties of the halogens as we proceed down the column from fluorine to
iodine, including the melting point, boiling point, intensity of the color of the halogen, the radius of the
corresponding halide ion, and the density of the element. On the other hand, there is a regular decrease in
the first ionization energy as we go down this column. As a result, there is a regular decrease in the oxidizing
strength of the halogens from fluorine to iodine.
F2 > Cl2 > Br2 > I2
oxidizing strength
Halogens
Halogen
Fluorine
Compounds
fluorides
Teflon (fluorocarbon)
Freon (fluorocarbon)
Chlorine
Bromine
Iodine
Properties
protect teeth against
decay
heat-resistant plastic
Uses
drinking water and
toothpaste
non-stick pans and
electrical insulation
refrigerant
hypochlorous acid and
hypochlorites
easily liquefied gas with
high heat of vaporization
powerful oxidizing agent,
germicide, bleaching agent
polyvinyl chloride (PVC)
tough plastic
silver bromide
light sensitive
bromides of sodium and
potassium
silver iodide, iodides of
sodium and potassium
sedative
purify water for drinking,
pools, sewage treatment,
bleaching industry,
household bleaches and
disinfectants
covering for furniture and
floors
photographic film, plates,
paper
headache powders
light sensitive, prevent
goiter
photography, make
‘iodized’ table salt
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