Other Group 6A elements Selenium is a semi-conductor; poor

conductor of electricity in dark, good in light; this makes it useful in photovoltaic cells, also used in photocopying machines

Te is rare, and its compounds are toxic

Halogens, Group 7A Do not exist in nature uncombined, but

their compounds are abundant; many of their sodium salts (NaF, NaI,NaCl,NaBr) are found in seawater; CaF2 is fluorspar- a mineral

All are nonmetals Fluorine and chlorine are gases and

yellowish to green; bromine is dark red liquid, iodine is a black solid ( vapors are purple)

All are very reactive ( they only need 1e-)

Most are water soluble All hydrogen halides, except HF, form

strong acids ( hi ionization)

Halogens, Group 7A

Chlorine Chlorine is 10th in the Top 50 list of chemicals

produced. It is a yellow, pungent and highly corrosive

gas. Cl2 is too reactive to occur free in nature. Chlorine occurs mostly as sodium chloride in

salt waters and mineral deposits. Industrial preparation - electrolysis of NaCl.

2NaCl (aq) + 2H2O (l) 2NaOH (aq) + Cl2 (g) + H2 (g)

ChlorineUsesAbout 70% of all chlorine is used in the chemical industry. In

many cases, the final compound does not even contain chlorine.

About 20% is used to bleach wood pulp and paper to make it white.

Another 5% is used for water treatment. Household bleach is made by allowing chlorine to react

with NaOH.Cl2 (aq) + 2NaOH (aq) NaOCl (aq) + NaCl (aq) + H2O (l)

Also used to make vinyl chloride and polyvinyl chloride (PVC)

Hydrochloric acid HCl is 27th on the Top 50 list of chemicals. Most is produced as a by-product of the

chlorination of organic compounds.CH4 (g) + 2Cl2 (g) CH2Cl2 (l) + 2HCl (g)

Hydrochloric acid is a strong acid. Concentrated HCl is produced by saturation

of water - approximately 12M. In the hardware store, you would find it under

the name muriatic acid.

Chlorine oxides Two oxides are made industrially, dichlorine

monoxide and chlorine dioxide. Both are used for bleaching paper and flour. A radical, ClO, has been studied as a result

of the role it plays in destruction of the ozone layer. Using Freon-12 as an example, CCl2F2:

CHLORINE Cl video

Fluorine Made by electrolyzing an ice-cold solution

of KF in HF (1886- Henri Moissan) Most chemically reactive of all nonmetals Strong oxidizing agent Forms compounds w/ elements except He,

Ne, Ar HF acid is used to etch glass Used to separate the isotopes of Uranium

Iodine and Bromine Br is obtained from sea water and salt-well

brines2NaBr(aq) + Cl2(g)------2NaCl(aq) + Br2(l)

Iodine used to be extracted from ashes of seaweeds; now it is produced from sodium iodate ( NaIO3)

Iodine is necessary for the thyroid gland to work properly