The Element Chlorine

The Element Chlorine Simplified

mass number of Chlorine

Atoms of the element Chlorine have 17 protons in the nucleus and 17 electrons orbit the nucleus in the neutral atom. Chlorine atoms are never found singly in nature and only very rarely are they found sharing electrons with other elements. They are usually found with a negative charge and a full outer shell of electrons.

The element Chlorine is important both to life and commercially. As a negatively charged ion Chlorine makes up one half of the common salt Sodium Chloride. Chlorine Gas, Cl2, is important in the production of plastics, treatment of drinking water, the pharmaceutical industry and cleaning products. Chlorine gas is not encountered in nature as it is highly reactive. It is expensive and energy intensive to manufacture.

Bohr diagram of Chlorine

Isotopes of The Element Chlorine

There are 23 possible isotopes of Chlorine. All have 17 protons with the number of neutrons in the nucleus varying. Since the neutrons carry no charge they do not affect the number of electrons the isotopes have and so all the isotopes have the same chemical properties. The number of neutrons ranges from 11 to 34. This gives these isotopes a total mass of between 28 and 51 subatomic particles.

Only two of these isotopes are stable. These are 35-Chlorine and 37-Chlorine which contain 18 and 20 neutrons respectively. The most common of these is 35-Chlorine which accounts for 75% of the Chlorine atoms in any natural sample.

The Electron Structure of Chlorine


outer shell electrons of Chlorine

The element Chlorine’s 17 electrons are arranged into three shells of electrons. The first two shells are completely filled and the last shell has 7 electrons. We can obtain this by looking at the electron details of Chlorine which gives the result 1s2 2s2 2p6 3s2 3p5.

This results in Chlorine having an identical outer shell electron pattern as Fluorine. This electron dot diagram is shown to the left. It tells us that Chlorine needs only one electron to fill its outer shell and achieve stability.

The subshell detail of Chlorine’s electron structure is shown below.

subshell electron distribution for Chlorine
The element chlorine as a Chloride ion

The Chloride Ion

Chlorine has one of the highest electronegativity values of any of the elements which means that its electrons are held very tightly to the nucleus. This makes Chlorine atoms prone to accepting a loose electron to complete its outer shell and therefore form the highly stable Chloride ion, Cl- as shown to the right.

As with its cousin Fluorine, the reason for the high degree of reactivity is a combination of core charge felt by the outer shell, and the number of electron shells, which combine to give a high electonegativity value for this element.

chlorine salt

In this state it is quite nonreactive since it will not release any of its electrons to elements less electronegative than itself which are few and far between.

Chloride ions will form compounds through Ionic Bonding with other elements. There is no sharing of electrons in these bonds, just attraction due to opposite charges. Sodium Chloride is an excellent example; it is made from Na+ ions and Cl- ions.

Chlorine Gas


chlorine gas and structure

It is possible to manufacture elemental or pure Chlorine gas from Chloride bearing solutions by supplying electricity. This requires a lot of electricity and the yellowish greenish Chlorine gas produced is very reactive and must be stored carefully and handled with caution.

Chlorine gas holds the unenviable title as the first chemical weapon to be used in significant quantities in the First World War. This was initially deployed by the Germans against Allied troops, but was later used by both sides before being replaced by more lethal substances.