Bromine

Atomic Number:

35

Symbol:

Br

Atomic Weight:

79.904

Discovery:

Balard 1826

Electron Configuration:

[Ar]4s²3d¹⁰4p⁵

Word Origin:

Greek bromos: stench

Uses:

Elemental bromine is used to manufacture a wide variety of bromine compounds used in industry and agriculture. Traditionally the largest use of bromine was in the production of 1,2-Dibromoethane which in turn was used as a gasoline anti-knock agent for leaded gasolines before they were largely phased out due to environmental considerations. Bromine is also used in making fumigants, flameproofing agents, water purification compounds, dyes, medicinals, sanitizers, inorganic bromides for photography, etc. It is also used to form intermediates in organic synthesis, where it is preferred to iodine due to its much lower cost. Bromine is used to make brominated vegetable oil, which is used as an emulsifier in many citrus-flavored soft drinks.

Sources:

Bromine is available commercially so it is not normally necessary to make it in the laboratory. Bromine also occurs in seawater as the sodium salt but in much smaller quantities than chloride. It is recovered commercially through the treatment of seawater with chlorine gas and flushing through with air. In this treatment, bromide is oxidized to bromine by the chlorine gas. The principle of oxidation of bromide to bromine is shown by the addition of a little chlorine water to aqueous solutions of bromide. These become brown as elemental bromine forms.

2Br^- + Cl₂ 2Cl^- + Br₂

Small amounts of bromine can also be made through the reaction of solid sodium bromide, NaBr, with concentrated sulphuric acid, H₂SO₄. The first stage is formation of HBr, which is a gas, but under the reaction conditions some of the HBr is oxidized by further H₂SO₄ to form bromine and sulphur dioxide. This reaction does not work with the corresponding chlorides and fluorides.

NaBr (s) + H₂SO₄ (l) HBr (g) + NaHSO₄ (s)

2HBr (g) + H₂SO₄ (l) Br₂ (g) + SO₂ (g) + 2H₂O (l)