Chlorine is a yellow-green gas at room temperature. It is an extremely reactive element and a strong oxidising agent: among the elements, it has the highest electron affinity and the third-highest electronegativity, behind only oxygen and fluorine.
While perhaps best known for its role in providing clean drinking water, chlorine chemistry also helps provide energy-efficient building materials, electronics, fiber optics, solar energy cells, 93 percent of life-saving pharmaceuticals, 86 percent of crop protection compounds, medical plastics, and much more.
Elemental chlorine is commercially produced from brine by electrolysis, predominantly in the chlor-alkali process.
Protons and Neutrons in Chlorine
Chlorine is a chemical element with atomic number 17 which means there are 17 protons in its nucleus. Total number of protons in the nucleus is called the atomic number of the atom and is given the symbol Z. The total electrical charge of the nucleus is therefore +Ze, where e (elementary charge) equals to 1,602 x 10-19 coulombs.
The total number of neutrons in the nucleus of an atom is called the neutron number of the atom and is given the symbol N. Neutron number plus atomic number equals atomic mass number: N+Z=A. The difference between the neutron number and the atomic number is known as the neutron excess: D = N – Z = A – 2Z.
For stable elements, there is usually a variety of stable isotopes. Isotopes are nuclides that have the same atomic number and are therefore the same element, but differ in the number of neutrons. Mass numbers of typical isotopes of Chlorine are 35; 37.
Main Isotopes of Chlorine
Chlorine has two stable isotopes, 35Cl and 37Cl. These are its only two natural isotopes occurring in quantity, with 35Cl making up 76% of natural chlorine and 37Cl making up the remaining 24%.The longest-lived radioactive isotope is 36Cl, which has a half-life of 301,000 years. All other isotopes have half-lives under 1 hour, many less than one second.
Chlorine-35 is composed of 17 protons, 18 neutrons, and 17 electrons.
Chlorine-37 is composed of 17 protons, 20 neutrons, and 17 electrons.
Chlorine-36 is composed of 17 protons, 19 neutrons, and 17 electrons. Trace amounts of radioactive 36Cl exist in the environment, in a ratio of about 7×10−13 to 1 with stable isotopes. 36Cl is produced in the atmosphere by spallation of 36Ar by interactions with cosmic ray protons.
Electrons and Electron Configuration
The number of electrons in an electrically-neutral atom is the same as the number of protons in the nucleus. Therefore, the number of electrons in neutral atom of Chlorine is 17. Each electron is influenced by the electric fields produced by the positive nuclear charge and the other (Z – 1) negative electrons in the atom.
Since the number of electrons and their arrangement are responsible for the chemical behavior of atoms, the atomic number identifies the various chemical elements. The configuration of these electrons follows from the principles of quantum mechanics. The number of electrons in each element’s electron shells, particularly the outermost valence shell, is the primary factor in determining its chemical bonding behavior. In the periodic table, the elements are listed in order of increasing atomic number Z.
Electron configuration of Chlorine is [Ne] 3s2 3p5.
Possible oxidation states are +1,5,7/-1.
It is an extremely reactive element and a strong oxidising agent: among the elements, it has the highest electron affinity and the third-highest electronegativity on the Pauling scale, behind only oxygen and fluorine. Because of its great reactivity, all chlorine in the Earth’s crust is in the form of ionic chloride compounds, which includes table salt. It is the second-most abundant halogen (after fluorine) and twenty-first most abundant chemical element in Earth’s crust.
Common Compound of Chlorine
The simplest chlorine compound is hydrogen chloride, HCl, a major chemical in industry as well as in the laboratory, both as a gas and dissolved in water as hydrochloric acid. It is often produced by burning hydrogen gas in chlorine gas, or as a byproduct of chlorinating hydrocarbons. Hydrogen chloride gas and hydrochloric acid are important in technology and industry.
|Number of protons
|Number of neutrons (typical isotopes)
|Number of electrons
|[Ne] 3s2 3p5