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Bromine
Elemental bromine exists as a diatomic molecule, Br2. It is a dense, mobile, slightly
transparent reddish-brown liquid, that evaporates easily atstandard temperature and
pressures to give an orange vapor (its color resembles nitrogen dioxide) that has a strongly
disagreeable odor resembling that of chlorine. It is one of only two elements on the periodic
table that are liquids at room temperature (mercury is the other, althoughcaesium, gallium,
and rubidium melt just above room temperature).
At a pressure of 55 GPa bromine converts to ametal. At 75 GPa it converts to a face centered
orthorhombic structure. At 100 GPa it converts to a body centered orthorhombic monoatomic
form.
Chemical
Being less reactive than chlorine but more reactive than iodine, bromine reacts vigorously with
metals, especially in the presence of water, to give bromide salts. It is also reactive toward
most organic compounds, especially upon illumination, conditions that favor the dissociation of
the diatomic molecule into bromine radicals:
Br2
2 Br·
It bonds easily with many elements and has a strong bleaching action.
Bromine is slightly soluble in water, but it is highly soluble in organic solvents such
as carbon disulfide, carbon tetrachloride, aliphatic alcohols, and acetic acid.
Isotopes
Main article: Isotopes of bromine
Bromine has two stable isotopes, Br (50.69 %) and Br (49.31%). At least 23
otherradioisotopes are known. Many of the bromine isotopes are fission products. Several
of the heavier bromine isotopes from fission are delayed neutron emitters. All of the
radioactive bromine isotopes are relatively short lived. The longest half-life is the neutron
deficient 77Br at 2.376 days. The longest half-life on the neutron rich side is 82Br at 1.471
days. A number of the bromine isotopes exhibit metastable isomers. Stable 79Br exhibits a
radioactive isomer, with a half-life of 4.86 seconds. It decays by isomeric transition to the
stable ground state.
Safety
Elemental bromine is toxic and causes burns. As an oxidizing agent, it is incompatible with
most organic and inorganic compounds. Care needs to be taken when transporting bromine; it
is commonly carried in steel tanks lined with lead, supported by strong metal frames.
When certain ionic compounds containing bromine are mixed with potassium
permanganate (KMnO4) and an acidic substance, they will form a pale brown cloud of bromine
gas.
6 Br– + 2 MnO4– + 8 H+ → 3 Br2 + 2 MnO2 + 4 H2O
This gas smells like bleach and is very irritating to the mucous membranes. Upon
exposure, one should move to fresh air immediately. If symptoms of bromine poisoning
arise, medical attention is needed.