What do hot tubs, marine algae and Tyrian purple have in common?

Elemental bromine in a borosilicate glass ampoule, sealed in an acrylic cube.

Image: Alchemist-hp (Creative Commons Attribution-Share Alike 3.0 Germany license.)

This week's element is bromine, which has the atomic number 35 and the atomic symbol Br. At room temperature, bromine is a reddish-brown liquid that gives off a very smelly and toxic orange vapour, similar to chlorine gas (although I think chlorine gas has a more noxious stench than does bromine).

Elemental bromine does not occur naturally in the wild, but bromine salts are found in the sea and in marine algaes. One discoverer of bromine, Antoine Balard, originally found it in the ash of seaweed in 1826. (Unknown at the time, bromine is found in high concentrations in marine algae because of an unique algal enzyme; vanadium bromoperoxidase.) Balard named his new element muride, from the Latin muria (brine), but later changed the name to brôme (bromine) from the Greek βρωμος for stench (of he-goats). Bromine was independently discovered by Carl Jacob Löwig in 1825 but publication of his results was delayed so Balard got precedence.

Today, bromine is most commonly used as a flame retardant in a variety of items and as a pesticidal fumigant. But I am most familiar with bromine from working with hot tubs, spas and swimming pools, where it is used as a more stable alternative to chlorine to sanitize water. I also know bromine from working in molecular biology labs, where ethidium bromide (EtBr), a DNA-intercalating agent, is used to visualise DNA under UV light. Bromine can act as a mutagen and some forms react with and deplete ozone, so bromine's use is being restricted and phased out where ever possible.

Bromine, as our favourite chemistry professor will tell us, is notable because it alone among the elements has two stable isotopes that occur naturally in roughly equal proportions, 79Br and 81Br. (However, it is interesting to note that bromine's "little sister", chlorine, also has two stable isotopes that occur in large, although unequal, quantities; 35Cl (76%) and 37Cl (24%)).

Visit periodicvideos's YouTube channel.

Since I am passionate about colour, especially the blue-purple portion of the visible spectrum, I just have to mention that the fabric dye, Tyrian purple, is made from an organic bromine-containing compound. This beautiful dye has been used by humans since ancient times. It is made from a brominated indole indigo dye produced by the predatory sea snail, Bolinus (Murex) brandaris (pictured at right: M. Violante/Creative Commons Attribution-Share Alike 3.0 Unported license). The organobromine nature of this compound was not discovered until 1909.



You've already met these elements:

Selenium: Se, atomic number 34
Arsenic: As, atomic number 33
Germanium: Ge, atomic number 32
Gallium: Ga, atomic number 31
Zinc: Zn, atomic number 30
Copper: Cu, atomic number 29
Nickel: Ni, atomic number 28
Cobalt: Co, atomic number 27
Iron: Fe, atomic number 26
Manganese: Mn, atomic number 25
Chromium: Cr, atomic number 24
Vanadium: V, atomic number 23
Titanium: Ti, atomic number 22
Scandium: Sc, atomic number 21
Calcium: Ca, atomic number 20
Potassium: K, atomic number 19
Argon: Ar, atomic number 18
Chlorine: Cl, atomic number 17
Sulfur: S, atomic number 16
Phosphorus: P, atomic number 15
Silicon: Si, atomic number 14
Aluminium: Al, atomic number 13
Magnesium: Mg, atomic number 12
Sodium: Na, atomic number 11
Neon: Ne, atomic number 10
Fluorine: F, atomic number 9
Oxygen: O, atomic number 8
Nitrogen: N, atomic number 7
Carbon: C, atomic number 6
Boron: B, atomic number 5
Beryllium: Be, atomic number 4
Lithium: Li, atomic number 3
Helium: He, atomic number 2
Hydrogen: H, atomic number 1



twitter: @GrrlScientist
facebook: grrlscientist


More from The elements
