We continue to review some of the most important materials in heat treatment and metallurgy.
Bromine (chemical symbol: Br)
Bromine is a hazardous, fuming red-brown liquid (Fig. 1) that evaporates quickly when exposed to air. Bromine’s amber-colored vapor has a pungent odor that can be irritating to the eyes, lungs and skin. Interestingly, it is the only nonmetallic element that is a liquid at room temperature. Pure bromine is very reactive and therefore does not occur freely in nature but can be found in minerals such as halide (rock-salt) deposits (Fig. 2). Bromine is considered one of the five elements in the halogen group of the periodic table, with the others being chlorine, fluoride, iodine and astatine. The term halogen means “salt-producing,” and when one of these elements reacts with a metal it will create salt crystals (the most common being sodium chloride).
Bromine’s discovery is credited to two different chemists working independently of one another: Carl Jacob Löwig in 1825 and Antoine Balard in 1826. Löwig, a German chemistry student, took local mineral water, added chlorine and mixed the two together with ether. He took the resulting reddish-brown substance, evaporated the ether and observed a brown liquid remained that was determined to be a new element. Balard, a French chemist, isolated bromine by studying a brown seaweed and using a sample of the brine in which it was found. Balard then distilled the brine with chlorine, which produced a dark-red liquid that had properties between those of chlorine and iodine. After subsequent testing, he determined that the liquid was neither a chlorine or iodine compound. Balard proposed a name for the new element, “muride,” after “muria” meaning “brine” in Latin.
In ancient times, a compound containing bromine was extracted from a type of sea mussel to create an expensive purple dye called tyrian purple (Fig. 3). In the earlier 20th century, much of the bromine used was in the manufacturing of ethylene dibromide (C2H4Br2), an additive to leaded gasoline to prevent lead buildup within engines. The favor of unleaded gasoline in recent decades has massively reduced the demand for bromine. Silver bromide (AgBr), a chemical used in photography, is now credited as the largest use of bromide commercially. Other compounds containing bromine can be found in fumigants, flameproofing agents and in some water purifiers.
Here are a few important facts about bromine.
- Atomic number: 35
- Atomic weight: 79.904
- Melting point: 265.95 K (-7.2°C or 19.0°F)
- Boiling point: 331.95 K (58.8°C or 137.8°F)
- Density: 3.11 grams per cubic centimeter
- Phase at room temperature: Liquid
- Element classification: Nonmetal
- Period number: 4
- Group number: 17
- Group name: Halogen
- Electron configuration: [Ar] 3d10 4s2 4p5
- KnowledgeDoor (www.knowledgedoor.com)
- Jefferson Lab (https://www.jlab.org)
- Wikipedia (www.wikipedia.org)
- Chemicool (www.chemicool.com)
- Ancient History Encyclopedia (https://www.ancient.eu)