Chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. It has a standard atomic weight of 35.45, sits in period 3 and group 17, and is classified as a halogen.
Properties
| Symbol | Cl |
|---|---|
| Atomic number | 17 |
| Standard atomic weight | 35.45 |
| Category | Halogen |
| Group | 17 |
| Period | 3 |
| Electron configuration | [Ne] 3s2 3p5 |
| Outer-shell electrons | 7 |
The figure of 35.45 is a conventional value, because IUPAC publishes an interval for this element rather than a single weight. For elements like this one the fourth digit carries real uncertainty, because the isotopic composition varies measurably between natural sources — so quoting eight digits would overstate what is known.
Compounds containing chlorine
62 of the compounds in this reference contain Cl, listed by the fraction of their mass it makes up.
| Compound | Formula | Atoms | % by mass |
|---|---|---|---|
| chlorine | Cl2 | 2 | 100.0% |
| hydrochloric acid | ClH | 1 | 97.2% |
| chloroform | CHCl3 | 3 | 89.1% |
| lithium chloride | ClLi | 1 | 83.6% |
| dichloromethane | CH2Cl2 | 2 | 83.5% |
| aluminium chloride | AlCl3 | 3 | 79.8% |
| magnesium chloride | Cl2Mg | 2 | 74.5% |
| phosgene | CCl2O | 2 | 71.7% |
| ammonium chloride | ClH4N | 1 | 66.3% |
| iron chloride | Cl3Fe | 3 | 65.6% |
| calcium chloride | CaCl2 | 2 | 63.9% |
| sodium chloride | ClNa | 1 | 60.7% |
| cobalt chloride | Cl2Co | 2 | 54.6% |
| copper chloride | Cl2Cu | 2 | 52.7% |
| zinc chloride | Cl2Zn | 2 | 52.0% |
| DDT | C14H9Cl5 | 5 | 50.0% |
| calcium hypochlorite | CaCl2O2 | 2 | 49.6% |
| sodium hypochlorite | ClNaO | 1 | 47.6% |
| potassium chloride | ClK | 1 | 47.6% |
| strontium chloride | Cl2Sr | 2 | 44.7% |
| epichlorohydrin | C3H5ClO | 1 | 38.3% |
| perchloric acid | ClHO4 | 1 | 35.3% |
| barium chloride | BaCl2 | 2 | 34.0% |
| sodium chlorate | ClNaO3 | 1 | 33.3% |
| 2,4-D | C8H6Cl2O3 | 2 | 32.1% |
Showing the 25 with the highest Cl content, of 62.
Calculate with chlorine
- Molar mass of any formula containing it
- Electron configuration, including ions
- Effective nuclear charge by Slater's rules
- Average atomic mass from isotope abundances
Group 17
Atomic weights are the IUPAC 2021 standard values, abridged to the conventional five significant figures. Group, period, category and electron configuration are derived from the atomic number rather than stored, so they cannot drift out of step with it.