Chlorine - Cl

Symbol Cl
Atomic Number 17
Atomic Mass 35.45
Discovered by Carl Wilhelm Scheele

What is Chlorine?

Chlorine is the second lightest halogen and is represented as Cl. The atomic number of this chemical element is 17.

It appears as a pale yellow-green gas. Liquid chlorine can cause skin burn and chlorine in its gaseous form irritates the mucous membrane. Its position as per the periodic table is between fluorine and bromine. Its electronic configuration is [Ne]3s23p5. There are two isotopes of chlorine that are stable.

They are 37Cl  and 35Cl. 36Cl is the stable radioisotope of chlorine. Sodium chloride is the most common compound of chlorine whereas the simplest is hydrogen chloride. Sodium chloride has a molecular formula NaCl whereas hydrogen chloride has a molecular formula HCl. It is highly reactive. Carl Wilhelm Scheele who was a Swedish chemist discovered Chlorine in the year 1774.

Table of Contents

Properties of Chlorine – Cl

Cl Chlorine
Atomic Number‎ 17
Atomic weight 35.453
Melting Point −101.5 °C
Boiling Point −34.04 °C

Chlorine is the second halogen in the periodic table, being a nonmetal in group 17. Hence, its properties are similar to fluorine, bromine, and iodine, and are generally intermediate among those of the first two. Chlorine has the electron configuration [Ne]3s23p5, with the seven electrons serving as its valence electrons in the third and outermost shell. As all halogens, it is thus one electron short of a full octet, and is thus a strong oxidizing agent, interacting with other elements to complete its outer shell.

This element is intermediate in the electronegativity between fluorine and bromine (the electronegativity of fluorine is 3.98, the electronegativity of chlorine is: 3.16, the electronegativity of bromine is 2.96, and the electronegativity of iodine is 2.66). This element is less reactive than fluorine and more reactive than bromine, in line with periodic patterns. Even though it is a weaker oxidizing agent than fluorine, it is stronger than bromine. In comparison, the chloride ion is a weaker reduction agent than bromide, but one stronger than fluoride.

Chlorine Structure – Cl

Chlorine Structure

The atomic number of chlorine is 17. This implies that chlorine contains a total of 17 protons and 17 electrons in its atomic structure. These electrons are arranged into 3 primary electron shells. The first electron shell belonging to chlorine contains a total of two electrons whereas the second electron shell of chlorine contains 8 electrons. Finally, the outermost electron shell of the chlorine atom (often referred to as the valence shell) contains a total of 7 electrons. Therefore, the valency of chlorine is often considered to be 7. However, it is important to note that chlorine needs only one more electron to complete its octet configuration. Therefore, the valency of chlorine can also be considered to be 1.

Uses of Chlorine (Cl)

  • It is used to get rid of the smell of putrefaction
  • It is used as a disinfectant
  • Chlorine is used in the treatment of drinking water to kill bacteria
  • It is used to clean swimming pools
  • It is used in the production of paper and paper products
  • It is used as an antiseptic
  • It is used to produce drugs
  • It is used in the manufacture of dyes and plastics

Frequently Asked Questions


What is the period of chlorine?

Chlorine is a periodic table in group 17, also known as halogens, and is not found in nature as the element-only as a compound. Salt, or sodium chloride, and potassium compounds sylvite are the most common.


Is chlorine volatile?

Chlorine is unstable as a result of fairly unlikely secondary exposure from exposed persons, but chlorine gas can condense on the skin and contaminate others through dermal contact.


How many electrons does Cl 35 have?

Chlorine contains 17 electrons. This means that there are 17 protons in each of these atoms. Seventeen electrons. Neutrons 35-17 = 18.


Why is chlorine gas Green?

At room temperature, chlorine is a yellow-green gas. Chlorine has a pungent, unpleasant, bleach-like odour that can be detected at low levels. The chlorine gas concentration is around 2.5 times greater than air, which will initially cause it to stay close to the ground in areas with low air movement.


Is chlorine a poisonous gas?

Gaseous chlorine is poisonous and is listed as an irritant to the lungs. It has intermediate water solubility with the ability to cause upper and lower respiratory tract acute damage. Due to its strong smell, chlorine gas can be easily detected.

Learn more about the atomic weight, electron configuration and the uses of Cl from the expert faculties at BYJU’S.

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  2. Physical properties and chemical properties of chlorine