Bromine: the essentials
- Name: bromine
- Symbol: Br
- Atomic number: 35
- Relative atomic mass (Ar): 79.904 range: [79.901, 79.907]
- Standard state: liquid at 298 K
- Appearance: red-brown, metallic lustre when solid
- Classification: Non-metallic
- Group in periodic table: 17
- Group name: Halogen
- Period in periodic table: 4
- Block in periodic table: p
- Shell structure: 126.96.36.199
- CAS Registry: 7726-95-6
Bromine atoms have 35 electrons and the shell structure is 188.8.131.52. The ground state electronic configuration of neutral bromine is [Ar].3d10.4s2.4p5 and the term symbol of bromine is 2P3/2.
Bromine is the only liquid nonmetallic element. It is a member of the halogen group. It is a heavy, volatile, mobile, dangerous reddish-brown liquid. The red vapour has a strong unpleasant odour and the vapour irritates the eyes and throat. It is a bleaching. When spilled on the skin it produces painful sores. It is a serious health hazard, and maximum safety precautions should be taken when handling it.
Cartoon by Nick D Kim ([Science and Ink], used by permission).
Bromine: physical properties
- Density of solid: 4050 kg m-3
- Molar volume: 19.78 cm3
- Thermal conductivity: 0.12 W m‑1 K‑1
Bromine: heat properties
- Melting point: 265.8 [‑7.3 °C (19 °F)] K
- Boiling point: 332 [59 °C (138 °F)] K
- Enthalpy of fusion: 20.5 kJ mol-1
Bromine: atom sizes
- Atomic radius (empirical): 115 pm
- Molecular single bond covalent radius: 114 (coordination number 1) ppm
- van der Waals radius: 186 ppm
- Pauling electronegativity: 2.96 (Pauling units)
- Allred Rochow electronegativity: 2.74 (Pauling units)
- Mulliken-Jaffe electronegativity: 2.95 (14.3% s orbital)
Bromine: orbital properties
- First ionisation energy: 1139.86 kJ mol‑1
- Second ionisation energy: 2083.2 kJ mol‑1
- Third ionisation energy: 3364.5 kJ mol‑1
- Universe: 7 ppb by weight
- Crustal rocks: 3000 ppb by weight
- Human: 2900 ppb by weight
Bromine: crystal structure
Bromine: biological data
- Human abundance by weight: 2900 ppb by weight
Bromine may be an essential trace element for red algae and possibly mammals. It is found in the mollusc pigment "royal purple", although its role is not understood. Excessive bromide intake leads to depression and of weight loss.
Reactions of bromine as the element with air, water, halogens, acids, and bases where known.
Bromine: binary compounds
Binary compounds with halogens (known as halides), oxygen (known as oxides), hydrogen (known as hydrides), and other compounds of bromine where known.
Bromine: compound properties
Bond strengths; lattice energies of bromine halides, hydrides, oxides (where known); and reduction potentials where known.
Bromine: historyBromine was discovered by Antoine-J. Balard in 1826 at France. Origin of name: from the Greek word "bromos" meaning "stench".
Both Bromine isotopes are used in nuclear medicine. Br-81 is used for the production of the radioisotope Kr-81m which is used for diagnostics. Br-79 can be used for the cyclotron production of Kr-77 which decays to the radioisotope Br-77 although the most common production route for Br-77 is via Se-77. Br-77 has been suggested for radiotherapy because of it electron capture decay and ease of labeling.
Isolation: 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)