Links/Connections

WITHIN CHEMISTRY

1. See Related Concepts and Skills for the most direct links.

2. Chemistry of halogens is very important in organic chemistry—many halo-organics
can be synthesized easily and have been found to have very useful properties.

3. Halogen chemistry has importance in inorganic chemistry—inorganic halides
provide starting materials for other inorganic species and organometallics. By
contrast, some halogen-containing substances, such as sulfur hexafluoride (SF₆ ),
are very inert dielectrics (and find use commercially because of their inertness).

BETWEEN CHEMISTRY AND OTHER DISCIPLINES

1. Agriculture. Organic halogen compounds are very important in agriculture.
Some important uses include polychlorinated organic compounds as
insecticides (such as DDT); fluoro and chloro aromatic heterocyclic compounds
and urea derivatives as herbicides; and chlorinated and organic compounds
as solvents. Chlorinated inorganic compounds include chlorine bleach as a
disinfectant, and salt blocks for animals in hot weather. For more details, see
“Organic Halogen Compounds” and “Halogens” entries in the Encyclopedia
Britannica or some other modern encyclopedia.

2. Environmental science . The escape of large numbers of chlorofluorocarbons
(Freons) into the upper atmosphere where they can react photochemically with
ozone is thought to be causing a depletion of the ozone layer, especially near the
South Pole. This problem involves an ironic twist—Freons are chemically inert
and have been used to replace toxic materials in many applications such as
refrigeration, where ammonia (which is very toxic when released in large
quantities) was the common refrigerant prior to synthesis of Freons. Environmental
science is also concerned with potential side effects, both in humans and nature,
of some agriculturally important haloorganics and with the effects that chlorination
of impure water supplies may have on formation of toxic haloorganics in water.

3. Hygiene. Halogen chemistry contributes to personal hygiene (e.g., dentifrices
containing tin(II) fluoride, sodium fluoride, or a fluorophosphate; antiperspirants
and deodorants containing aluminum chlorhydrate; and other preparations
containing sodium chloride). In the public health arena, water purification with
chlorine is considered so important that all public water supplies in the United
States must be treated with chlorine. Chlorine is also used to treat sewage
sludge. Although an excellent antibacterial, pHisohex is only available by
prescription; doctors use it for surgical scrubbing in certain cases only.

4. Photography. Silver halides (particularly AgBr, though AgCl and AgI have
been used as well) are the basis of the photographic industry. For more
details, see the Photochemistry module.

5. Polymer science . Polyvinyl chloride, PVC = (CH₂–CHCl)n , is useful in a
variety of common applications, including electrical insulation, rainwear
fabrics and upholstery fabrics. Poly(tetrafluoroethylene) [Teflon = (CF₂–CF₂ )_n ]
and poly(chlorotrifluoroethylene) [Kel–F = (CClF–CF₂ ) n ] have excellent electrical
resistance, thermal stability, heat conductivity, and low intermolecular forces
(low friction) and are used for thermal coatings, bearings, lubricants (in low
molecular weight forms), heat transfer insulators, etc. Viton-fluorinated
copolymers are related derivatives that are very thermally stable elastomers.

Community

Field Trips

1. Water plant to see chlorination of water process

2. Sewage disposal plant to see chlorination of sewage sludge and     reclaimed water

3. Manufacturing facilities as appropriate
 

Societal

1. See Discussion Activities .

2. Air conditioning has become widespread as a result of Freon use. If Freon use were to be discontinued immediately as a result of ozone layer depletion, finding a substitute that does not have even more serious problems would be a real concern.

3. Deodorants and air quality; see Discussion Activities.