The group 17 elements: the halogens

Bromine

Bromine was discovered independently by two chemists Antoine Balard ( [link] ) in 1825 and Carl Jacob Löwig ( [link] ) in 1826.

Balard found bromide salts in the ash of sea weed from the salt marshes of Montpellier. The sea weed was used to produce iodine, but also contained bromine. Balard distilled the bromine from a solution of seaweed ash saturated with chlorine. The properties of the resulting substance resembled that of an intermediate of chlorine and iodine; with those results he tried to prove that the substance was iodine monochloride (ICl), but after failing to do so he was sure that he had found a new element and named it muride , derived from the Latin word muria for brine.

In contrast, Löwig isolated bromine from a mineral water spring in Bad Kreuznach. Löwig used a solution of the mineral salt saturated with chlorine and extracted the bromine with Et ₂ O. After evaporation a brown liquid remained. Unfortunately, the publication of his results were delayed and Balard published first.

Iodine

Iodine was discovered by Bernard Courtois ( [link] ) in 1811 when he was destroying the waste material from the production of saltpeter (KNO ₃ ) during gunpowder production. Saltpeter produced from French niter beds required sodium carbonate (Na ₂ CO ₃ ), which could be isolated from seaweed washed up on the coasts of Normandy and Brittany. To isolate the sodium carbonate, seaweed was burned and the ash then washed with water; the remaining waste was destroyed by the addition of sulfuric acid (H ₂ SO ₄ ). After adding too much acid, Courtois observed a cloud of purple vapor that crystallized on cold surfaces making dark crystals. Courtois suspected that this was a new element but lacked the money to pursue his observations. In supplying samples to his friends, Charles Desormes and Nicolas Clément, he hoped his research was to continue. On 29 November 1813, Dersormes and Clément made public Courtois’s discovery, describing the substance to a meeting of the Imperial Institute of France.

Astatine

The existence of eka-iodine had been predicted by Mendeleev ( [link] ), but astatine was first synthesized in 1940 by Corson ( [link] ), MacKenzie ( [link] ), and Segrè ( [link] ) at the University of California, Berkeley by bombarding bismuth with alpha particles.

Abundance

The abundance of the halogens is given in [link] .

Isotopes

The naturally abundant isotopes of the halogens are listed in [link] . All 33 isotopes of astatine are radioactive.