Chlorine – Occurrence, Properties, Uses & More


Chlorine is the second element of the 17th group and the member of the halogen series compounds that form salts. Chlorine has seventeen electrons and seventeen protons and eighteen neutrons. The atomic number of chlorine is 17 whereas its atomic mass is 35.

Occurrence of Chlorine

Chlorine due to its reactivity is rarely present in elemental form. it is present in Earth’s crust and ocean in abundance but is bonded mostly with sodium as sodium chloride. The minerals on Earth such as halite, carnallite, and sylvite contain large amounts of chlorine. In gaseous form, it is diatomic Cl2. It is the major constituent of hydrochloric acid.


Naming and History of Chlorine

The name chlorine is derived from the Greek word “khloros” which means greenish-yellowish and was given by Sir Humphrey Davy.

Before the elemental discovery of chlorine, chemists only knew hydrochloric acid. Chlorine element was first prepared by Carl Wilhelm Scheele, the Swedish pharmacist. He heated hydrochloric acid with pyrolusite which is manganese dioxide. A greenish-yellowish gas was released with a choking smell, but he had no idea that he just discovered chlorine.

In 1807, sir Humphrey Davy investigated this and concluded that this was not oxygen or some other simple substance. It was chlorine in the gaseous form and in 1810 he suggested the name chlorine or chloric gas.

It took ten years for scientists to accept that chlorine is an element.

Properties of Chlorine

Due to its highly reactive nature, chlorine generally exists in bonded form with other elements such as sodium, calcium, and potassium. Being a member of the halogen family, it mostly forms salts of sodium, calcium, potassium, etc. in its pure form it is greenish-yellowish gas.

The chlorine in gas form is very dangerous for human health. It is a respiratory irritant and can cause pulmonary diseases. It can cause severe burns and ulcerations on the skin and is an eye irritant.

The melting point of chlorine is -101.5 ᵒC and the boiling point is -34.04 ᵒC.

Uses of Chlorine

Chlorine is an essential chemical in water purification, disinfectants, bleach, and mustard gas.

As disinfectant

Chlorine is utilized to make chlorine bleach, which whitens and sanitizes clothes and disinfects kitchen and bathroom surfaces. Diluted bleach and water solutions are especially efficient at eliminating bacteria that may be present on surfaces in houses that make people ill.


Water purification

Chlorine helps in cleaning and disinfecting drinking water and keeps the swimming pool safe. It is utilized to kill germs and other microbes from drinking water products.

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Chlorine is also used commonly in the manufacture of many substances and products directly or indirectly, i.e., in paper production, antibacterial, dyestuffs, food, insecticides, paints, petroleum products, plastics, medications, fabrics, solvents, and lots of other consumer items.

Chlorine is also utilized in organic procedures– for instance, as an oxidizing agent and a substitute for hydrogen. When utilized as a hydrogen substitute, chlorine can bring numerous desired properties in natural compounds, such as its disinfecting properties or its capability to form helpful substances and products like PVC and synthetic rubber.

About 20% of chlorine produced is utilized to make PVC. This is a flexible plastic utilized in window frames, vehicle interiors, electrical circuitry insulation, water pipes, blood bags, and vinyl floor covering.

Chlorine is also used in medicines, blood bags, respiratory inhalants, and other medical devices.

Isotopes of Chlorine

Chlorine has 24 isotopes but only two of them are stable. 35 Cl has a natural abundance of 75 % and 37 Cl has a natural abundance of 24 %. These stable isotopes are used in studies of supplied forms of NaCl and to check the toxicity level of environmental pollutants.


  • What is the atomic number of chlorine?
    • A) 16
    • B) 17
    • C) 18
    • D) 19
    • Answer: B
  • In which form is chlorine rarely present due to its reactivity?
    • A) Elemental form
    • B) Gaseous form
    • C) Liquid form
    • D) Solid form
    • Answer: A
  • What is the major constituent of hydrochloric acid?
    • A) Sodium
    • B) Chlorine
    • C) Oxygen
    • D) Hydrogen
    • Answer: B
  • Who named chlorine and what does the name signify?
    • A) Carl Wilhelm Scheele, greenish-yellowish color
    • B) Sir Humphrey Davy, yellow gas
    • C) Carl Wilhelm Scheele, choking smell
    • D) Sir Humphrey Davy, greenish-yellowish color
    • Answer: D
  • How was chlorine first prepared?
    • A) Heating hydrochloric acid with manganese dioxide
    • B) Reacting sodium with chlorine gas
    • C) Distilling chlorine from seawater
    • D) Burning chlorine crystals
    • Answer: A
  • At what temperature does chlorine exist in gas form?
    • A) 0 ᵒC
    • B) -34.04 ᵒC
    • C) -101.5 ᵒC
    • D) 100 ᵒC
    • Answer: C
  • What family does chlorine belong to in the periodic table?
    • A) Alkali metals
    • B) Noble gases
    • C) Halogens
    • D) Transition metals
    • Answer: C
  • What is the color of pure chlorine in its gas form?
    • A) Red
    • B) Blue
    • C) Greenish-yellowish
    • D) Purple
    • Answer: C
  • What health hazards are associated with chlorine gas?
    • A) Causes itching
    • B) Causes burns and ulcerations
    • C) Improves respiratory health
    • D) Enhances vision
    • Answer: B
  • What is the primary use of chlorine as a disinfectant?
    • A) Whitening teeth
    • B) Sanitizing clothes
    • C) Disinfecting kitchen surfaces
    • D) Enhancing flavor in food
    • Answer: B
  • In what form is chlorine commonly used for water purification?
    • A) Liquid
    • B) Gas
    • C) Solid
    • D) Aqueous solution
    • Answer: B
  • What percentage of chlorine is utilized to make PVC?
    • A) 10%
    • B) 20%
    • C) 30%
    • D) 40%
    • Answer: B
  • Which of the following is NOT a use of chlorine?
    • A) Paper production
    • B) PVC manufacturing
    • C) Chocolate production
    • D) Water pipes
    • Answer: C
  • How many stable isotopes does chlorine have?
    • A) 1
    • B) 2
    • C) 3
    • D) 4
    • Answer: B
  • What is the natural abundance of the stable isotope 35 Cl?
    • A) 50%
    • B) 60%
    • C) 75%
    • D) 90%
    • Answer: C
  • What element is chlorine bonded with in Earth’s crust and oceans?
    • A) Calcium
    • B) Sodium
    • C) Potassium
    • D) Iron
    • Answer: B
  • Who first prepared chlorine and how was it done?
    • A) Sir Humphrey Davy, heating hydrochloric acid
    • B) Carl Wilhelm Scheele, reacting sodium with chlorine gas
    • C) Sir Humphrey Davy, burning chlorine crystals
    • D) Carl Wilhelm Scheele, heating hydrochloric acid with manganese dioxide
    • Answer: D
  • What does the name “chlorine” mean in Greek?
    • A) Yellow gas
    • B) Greenish-yellowish
    • C) Choking smell
    • D) Respiratory irritant
    • Answer: B
  • What is the boiling point of chlorine?
    • A) -101.5 ᵒC
    • B) -34.04 ᵒC
    • C) 0 ᵒC
    • D) 100 ᵒC
    • Answer: B
  • Which of the following is NOT a property of chlorine?
    • A) Respiratory irritant
    • B) Skin burns and ulcerations
    • C) Enhances vision
    • D) Greenish-yellowish gas
    • Answer: C
  • What is the primary use of chlorine in water purification?
    • A) Enhancing taste
    • B) Killing germs and microbes
    • C) Providing color
    • D) Improving odor
    • Answer: B
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In conclusion, this tutorial on Chlorine covered its occurrence, naming, history, properties, uses, and isotopes. Chlorine, as the second element in the 17th group and a member of the halogen series, is rarely found in its elemental form due to its high reactivity. It predominantly occurs in Earth’s crust and oceans, bonded with sodium as sodium chloride. The name “chlorine” is derived from the Greek word “khloros,” meaning greenish-yellowish, as given by Sir Humphrey Davy.

Chlorine’s history involves its discovery by Carl Wilhelm Scheele, who accidentally produced the greenish-yellowish gas while heating hydrochloric acid. Sir Humphrey Davy later confirmed its gaseous form and suggested the name chlorine in 1810. The tutorial emphasizes that it took ten years for scientists to accept chlorine as an element.

Discussing the properties of chlorine, its highly reactive nature leads it to exist in bonded forms with elements like sodium, calcium, and potassium. In its pure form, chlorine is a greenish-yellowish gas, posing health hazards such as respiratory irritations, pulmonary diseases, and skin burns.

The uses of chlorine include its essential role in water purification, disinfectants, bleach, and even mustard gas. As a disinfectant, chlorine is used to produce bleach, which has applications in sanitizing clothes and surfaces. Chlorine’s role in water purification ensures the safety of drinking water and swimming pools by eliminating germs and microbes.

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Chlorine’s broader applications extend to the manufacture of various substances like paper, antibacterial agents, dyestuffs, insecticides, paints, plastics, medications, fabrics, and more. About 20% of chlorine production is used to make PVC, a versatile plastic widely employed in diverse products. Additionally, chlorine finds applications in the medical field, including medicines, blood bags, respiratory inhalants, and various medical devices.

Lastly, the tutorial touches on the isotopes of chlorine, highlighting that it has 24 isotopes, but only two of them are stable—35 Cl and 37 Cl, with natural abundances of 75% and 24%, respectively. These stable isotopes play a crucial role in studying forms of NaCl and assessing the toxicity level of environmental pollutants.