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R32 Elements Handbook
Elements HandbookHandbook
Group 7A: Halogens
Fluorine | discovered in 1886 by Henri Moissan
Chlorine | discovered in 1774 by Carl Wilhelm Scheele
Bromine | discovered in 1826 by Antoine-Jérôme Balard
Iodine | discovered in 1811 by Bernard Courtois
Astatine | discovered in 1940 by Dale R. Corson, K. R. Mackenzie, & Emilio Segrè
Physical Properties
- Halogens are nonmetals. At room temperature, fluorine and chlorine are gases and bromine is a liquid. Iodine and astatine are solids.
- Halogens are very reactive. The reactivity decreases from fluorine to astatine. Halogens do not exist in the elemental form in nature.
- Astatine isotopes are radio- active with short half-lives.
There are vapors in the bromine and iodine tubes because bromine is volatile and iodine sublimes easily at room temperature.
Sources
- Chlorine gas is made commercially by the electrolysis of brine. 2NaCl( aq ) 2H 2 O( l ) Cl 2 ( g ) H 2 ( g ) 2NaOH( aq )
- Bromine is obtained from seawater by a displacement reaction with chlorine. 2NaBr( aq ) Cl 2 ( g ) 2NaCl( aq ) Br 2 ( l )
- Iodine is found in brine and in sodium iodate, NaIO 3 , in deposits of sodium nitrate. Iodine is produced from NaIO 3 by this redox reaction. 2NaIO 3 ( aq ) 5NaHSO 3 ( aq ) I 2 ( g ) 2Na 2 SO 4 ( aq ) 3NaHSO 4 ( aq ) H 2 O( l ) - Fluorine is made by the electrolysis of potassium fluoride, KF, dissolved in liquid hydrogen fluoride, HF.
Fluorite, CaF 2 , is the principal mineral of fluorine. The term fluorescent comes from this mineral, which glows in the presence of UV radiation.
85
At
Astatine (210)
(^28) (^1832) (^187)
53
Iodine 126.
(^28) (^1818) 7
35
Br
Bromine 79.
(^28) (^187)
17
Cl
Chlorine 35.
(^28) 7
9
F
Fluorine 18.
27^ Br^2
Cl 2
2
Density 4.
3.
2 1 0
3
4
5
Density (g/cm
3 )
1.81 10 ^3
3.21 10 ^3
F Cl Br
Melting and Boiling Points
0
300
200
100
100
200
Temperature (
C)^114
184
59 (^35) 7 101 mp
(^188) bp
F Cl Br
220
Richard Megna/Fundamental Photographs
1987 Paul Silverman/Fundamental Photographs
Group 7A: Halogens R
Atomic Properties
- Group 7A elements have an electron configuration that ends in ns^2 np^5.
- Halogens exist as diatomic molecules.
- Each halogen has the highest electronegativity in its period.
- The most common ionic charge for halogens is 1. Except for fluorine, halogens also have positive oxidation numbers of 1, 3, 5, and 7. Chlorine forms four anions with oxygen. The oxidation number of chlorine is different in each anion.
Important Compounds and Reactions
- Halogens form metal halides. Example:
2Na( s ) Cl 2 ( g ) 2NaCl( s ) H 411 kJ/mol
- Halogens form hydrogen halides. Example:
H 2 ( g ) Cl 2 ( g ) 2HCl( g ) H 92.3 kJ/mol
- Dry bleach is a mixture of compounds represented by the formula CaCl(ClO). Dry bleach is used to bleach paper and textiles. It also removes stains and disinfects laundry. Ca(OH) 2 ( aq ) Cl 2 ( g ) CaCl(ClO)( aq ) H 2 O( l )
- Small amounts of oxygen are produced in the laboratory by heating potassium chlorate, KClO 3. Potassium chlorate is an oxidizing agent in fireworks, matches, and explosives. 2KClO 3 ( s ) 2KCl( s ) 3O 2 ( g )
- Canisters of sodium chlorate are used on submarines to produce oxygen. They are carried on airplanes in case of an emergency.
- Chlorine is used to make the monomer vinyl chloride, CH 2 “ CHCl, which reacts to form the polymer polyvinyl chloride (PVC). - Hydrofluoric acid (HF) is made from the mineral fluorite and sulfuric acid. Although HF is extremely dangerous, it has many uses, including cleaning metals and frosting glass. CaF 2 ( s ) H 2 SO 4 ( aq ) 2HF( g ) CaSO 4 ( s ) - Nonstick pans are coated with a polymer of tetrafluoroethene, F 2 C “ CF 2. - Tincture of iodine is a solution of iodine, I 2 , and potassium iodide, KI, in alcohol. It is an example of an iodine-based skin disinfectant.
Chlorine reacts vigorously with sodium to form solid sodium chloride.
Electronegativity
0
Electronegativity
4.
2.5 (^) 2.
3.0 (^) 2.
F Cl Br At
First Ionization Energy
1681
(^1009 )
(^1256 )
600
0
1200
1800
Energy (kJ/mol)
F Cl Br At
Atomic radius (pm)
Ionic radius (pm)
F Cl Br I At
F –^ Cl –^ Br –^ I–
62 102 120 140 140
133 181 196 220
Hypochlorite Chlorite
1 1
Chlorate
1
Perchlorate
1
Richard Megna/ Fundamental Photographs
Group 7A: Halogens R
F Artificial Blood
The most important function of blood is its ability to deliver oxygen from the lungs to cells throughout the body, and carry carbon dioxide from the cells to the lungs. Blood transfusions have been the traditional response to blood loss due to severe injuries or surgery. Blood transfusions have saved millions of lives. But it takes time to determine the recipient’s blood type and less common blood types may not be available. Also, blood can carry disease-causing bacteria and viruses.
Some artificial blood contains perfluorocarbons (PFCs). PFCs are organic compounds in which all the hydrogen has been replaced by fluorine. PFCs can dissolve and transport large quantities of oxygen. PFCs are mixed with emulsifiers and salts that mimic the composition of blood, minus the cells.
Large amounts of PFCs can be manufactured and their purity controlled. PFCs can deliver oxygen to areas where blood flow is restricted by narrowed arteries or tumors. In current trials, artificial blood is used to delay the need for blood transfusions during surgery. Because PFCs carry less oxygen than hemo- globin does, the patient must breathe oxygen-rich air.
Because blood is so complex, scientists may never find a sub- stitute to perform all its functions. Therefore, there is still a great need for donations of human blood. ■
The liquid in the beaker is a perfluorocarbon that is saturated with oxygen. The mouse survived by absorbing oxygen from the liquid in its lungs.
I Iodized Salt
The thyroid gland produces hormones that help to control the body’s growth and the energy produced by cells. Trace amounts of iodine are needed to produce thyroid hormones. An adult needs about 150 mg of iodine daily.
Ocean fish are a good source of iodine. When people used to get most of their food from local sources, a person who lived far from the ocean often had an iodine deficiency.
To compensate for the lack of iodine, the thyroid gland might enlarge. A severe deficiency could cause mental retardation. Adding potassium iodide to table salt proved to be a simple solution to this public health problem.
In the United States, iodized salt was first sold in 1924. There is about 400 mg of iodine in a teaspoon of iodized salt.
The use of iodized salt has virtually eliminated the problem of iodine deficiency in the United States. ■
DidDid YouYou Know...Know...
The purple dye prized by Roman emperors and other rulers contains bromine. The dye was extracted from the mollusk Murex brandaris, which lives in the Mediterranean Sea.
Group 7A: Halogens R
Gwen Rosenberg/Alliance Pharmaceutical Corp.
Carolina Biological Supply Company/Phototake
