Chlorine: the essentials
- Name: chlorine
- Symbol: Cl
- Atomic number: 17
- Relative atomic mass (Ar): 35.45 range: [35.446, 35.457] m [see notes g m]
- Standard state: gas at 298 K
- Appearance: yellowish green
- Classification: Non-metallic
- Group in periodic table: 17
- Group name: Halogen
- Period in periodic table: 3
- Block in periodic table: p
- Shell structure: 2.8.7
- CAS Registry: 7782-50-5
Chlorine atoms have 17 electrons and the shell structure is 2.8.7. The ground state electronic configuration of neutral chlorine is [Ne].3s2.3p5 and the term symbol of chlorine is 2P3/2.
Chlorine is a greenish yellow gas which combines directly with nearly all elements. Chlorine is a respiratory irritant. The gas irritates the mucous membranes and the liquid burns the skin. As little as 3.5 ppm can be detected as an odour, and 1000 ppm is likely to be fatal after a few deep breaths. It was used as a war gas in 1915. It is not found in a free state in nature, but is found commonly as NaCl (solid or seawater).
Chlorine: physical properties
- Density of solid: 2030 kg m-3
- Molar volume: 17.39 cm3
- Thermal conductivity: 0.0089 W m‑1 K‑1
Chlorine: heat properties
- Melting point: 171.6 [‑101.5 °C (‑150.7 °F)] K
- Boiling point: 239.11 [‑34.04 °C (‑29.27 °F)] K
- Enthalpy of fusion: 20.5 kJ mol-1
Chlorine: atom sizes
- Atomic radius (empirical): 100 pm
- Molecular single bond covalent radius: 99 (coordination number 1) ppm
- van der Waals radius: 182 ppm
- Pauling electronegativity: 3.16 (Pauling units)
- Allred Rochow electronegativity: 2.83 (Pauling units)
- Mulliken-Jaffe electronegativity: 3.10 (14.3% s orbital)
Chlorine: orbital properties
- First ionisation energy: 1251.19 kJ mol‑1
- Second ionisation energy: 2297.67 kJ mol‑1
- Third ionisation energy: 3840 kJ mol‑1
- Universe: 1000 ppb by weight
- Crustal rocks: 170000 ppb by weight
- Human: 1200000 ppb by weight
Chlorine: crystal structure
Chlorine: biological data
- Human abundance by weight: 1200000 ppb by weight
Chlorine as chloride (Cl-) is essential for mammals and plants. Digestive juices in the stomache contain hydrochloric acid.
Reactions of chlorine as the element with air, water, halogens, acids, and bases where known.
Chlorine: binary compounds
Binary compounds with halogens (known as halides), oxygen (known as oxides), hydrogen (known as hydrides), and other compounds of chlorine where known.
Chlorine: compound properties
Bond strengths; lattice energies of chlorine halides, hydrides, oxides (where known); and reduction potentials where known.
Chlorine: historyChlorine was discovered by Carl William Scheele in 1774 at Sweden. Origin of name: from the Greek word "chloros" meaning "pale green".
Both Chlorine isotopes, Cl-35 and Cl-37, are used to study the toxicity of environmental pollutant and are usually supplied in the form of NaCl.
Isolation: it is rarely necessary to make chlorine in the laboratory as it is readily available commercially in cylindes. Chlorine is found largely in seawater where it exists as sodium chloride. It is recovered as a reactive, corrosive, pale green chlorine gas from brine (a solution of sodium chloride in water) by electrolyis. Electrolysis of molten salt, NaCl, also succeeds, in which case the other product is sodium metal rather than sodium hydroxide.
Na+ + Cl- + H2O → Na+ + 1/2Cl2 + 1/2H2 + OH-
In the laboratory under carefully controlled conditions, chlorine can be made by the action of an oxidizing agent such as manganese dioxide, MnO2, upon concentrated hydrochloric acid - the same reaction used by Scheele in 1774 when discovering chlorine.
MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O