The Element Chlorine
Introduction to Chlorine
The element chlorine of the periodic table is a clear yellowish-green gas. It belongs to the halogen family of elements, along with fluorine and bromine. It gets its name from the Greek word Kloros, meaning greenish-yellow. Chlorine typically exists in nature as a diatomic element but the single species Cl- is essential to many compounds. Chlorine has a storied history of its use for atrocities in war but it also has numerous applications and uses in our modern world from food to consumer products to the environment.
Interesting Facts about Chlorine
- As one of the diatomic elements, along with hydrogen, fluorine, iodine, bromine, oxygen, and nitrogen, lone chlorine atoms seldom exist in nature
- Chlorine is the ninth most abundant element in the human body
- Chlorine is the third most abundant element in the earth’s oceans
- Gaseous chlorine is so pungent most humans can detect the smell of it in concentrations as low as 3.5 ppm
- Chlorine is the 21st most abundant element in the earth’s crust
- In organic chemical reaction mechanisms, chlorine often replaces hydrogen atoms within molecules
- The first-ever chain chemical reaction was observed by German chemist Max Bodenstein in 1913 when he made chlorine and hydrogen gas explode upon light exposure
- Although its primary oxidation number is a negative one, chlorine can on rare occasions exhibit plus one, +3, +4, +5, +6, and +7
- Oxyacids occur when chlorine reacts with alkaline solutions
- In the lab, chemists prepare chlorine through oxidizing hydrochloric acid with permanganate salts
Chlorine Element in the Periodic Table
Chlorine, atomic symbol Cl, has an atomic number of 17 and lies in group 17, the halogen group, of the periodic table. The element is situated below fluorine, to the right of sulfur, to the left of neon, and above bromine. Specifically, chlorine lies in the third period. It has seven valence electrons and has extremely high reactivity. It will form compounds with all elements except for krypton, argon, neon, and helium. These noble gases tend to not form compounds with anything!
Chlorine has an electronegativity of 3.16 on the Pauling scale. Its full electron configuration is 1s22s22p63s23p5.
The Chlorine Element in Our Bodies
Most people consume around 6 g of chlorine per day in the form of sodium chloride, also known as table salt. People have long feared the possible negative health consequences of salt overconsumption, despite the fact that it is an essential mineral for the body. We now know that proper hydration and exercise effectively counteracts any salt overconsumption. The body can remove excess sodium through sweat and urination. At any given time, chlorine (in the form of chloride) can exist in the blood at approximately 0.3% concentration, in the bones at 900 ppm, and in tissue at 0.2 to 0.5% concentration. The human body has around 95 g of chlorine in total at any given time.
Chlorine also plays a role in the function of the human immune system. In 1996, The Journal of Clinical Investigation published a paper describing how white blood cells produce small volumes of chlorine gas in order to defend the body against invasive pathogens.
Stomach acid, responsible for doing the heavy lifting of food digestion, primarily contains hydrochloric acid. Without such a strong acid, we would be unable to digest proteins into their separate amino acid components.
Applications of Chlorine Element in the World Today
In industry, chlorine is produced via electroless use of brine. Chemical industry uses around 30% of the chlorine gas produced today. Specifically, 20% is used for water purification, 10% is used in bleachers, 15% is used in solvents, and about a quarter of chlorine produced is used for PVC (polyvinyl chloride).
Bleaches made with chlorine have a wide range of uses. Recycling firms use them to remove ink before recycling paper. Paper manufacturers also use chlorine to produce wood pulp. Outside of direct involvement, companies also indirectly use chlorine in many noteworthy industrial processes.
Around 85% of pharmaceutical drugs require the use of chlorine at some point in their production. Pharmaceutical companies use chlorine in the manufacturing process of both silicones and polymers. Interestingly, the finished products typically do not contain chlorine.
Consumer products that contain chlorine include pesticides, paint strippers, flame retardants, and domestic bleaches. These are examples of products in which chlorine is essential to makeup.
PVC is a well-known use of chlorine. Of note, PVC has diverse applications such as the creation of blood transfusion bags, double glazing window frames, water bottles, outdoor furniture, electrical insulation, and vinyl flooring just to name a few. Incredibly, PVC has proven to be one of the most marketable discoveries of modern chemistry.
As first mentioned, many industrial chemicals include chlorine, most notably carbon tetrachloride, chloroform, sodium hypochloride, and hydrochloric acid. Once widespread outside of the industry, the aforementioned chemicals now have strict regulations due to their damaging health effects on those who do not handle them properly.
In Maidstone, England, in 1897, chlorine was first discovered to be useful in disinfecting tap water. Purification then became the standard method throughout great Britain, later spreading to the rest of the developed world at the time. Usually, water purifiers bubble chlorine from hypochlorite bleach up a column of water. A solution of alkali sodium hydroxide then trickles down, forming NaOCl, a strong oxidizing agent. NaOCl is generally safe, can remain stable for several months, and readily kills bacteria and viruses.
While many have used chlorine to promote human prosperity, others have famously used it as an element of war. The German army released hundreds of cylinders of chlorine gas onto British troops in Flanders on the morning of April 22, 1915, marking the beginning of the age of chemical warfare. Another chlorine-based gas, phosgene (carbon oxychloride, COCl2), also served as a suffocating agent during the First World War.
The 20th century also saw chlorine used to innovate for peaceful reasons. The insecticide DDT, which contains five chlorine atoms per molecule, became widespread during the 1940s and 50s. However, American biologist Rachel Carson discovered that the compound was highly carcinogenic, and also had a devastating impact on the environment in the food chain. After showing DDT reduced the local songbird population, the compound became heavily restricted by law. Her findings are seen generally as the genesis of the modern environmentalism movement.
Chlorine is also famously known for being used to treat swimming pools. Hypochlorite compounds are added to the water, dissolving into elemental chlorine, which is very effective at killing harmful microbes.
When and How was Chlorine Discovered?
A substance that would eventually be proven to be chlorine was first described by Flemish chemist Jan Baptista Van Helmont in the 1630s. It was similarly identified by German chemist Carl Wilhelm Scheele in 1774, who was able to perform further experimentation on it but was still unable to isolate and identify the new element. He produced elemental chlorine by reacting hydrochloric acid with manganese (IV) oxide. Interestingly, he noted that the gas product readily reacted with metals and had a pungent smell. Consequently, Scheele called the substance ” dephlogisticated muriatic air”. Chlorine was officially identified and named by British chemist Sir Humphry Davy in the year 1810.
Where is Chlorine Present in the Universe?
Chlorine is found in great abundance in seawater in the form of salt but is also found in the earth’s crust. Minerals such as carnallite and sylvite are chlorine-containing.
Chlorine Element Chemistry: Compounds, Reactions, Properties, Ions
Chlorine is a dense, pungent, and highly reactive gas. It is soluble in water. About 3 L of gas will dissolve in 1 L of water at 10°C. Chlorine reacts with nearly all elements, save for the noble gases. In some reactions, it will form multiple stable chlorides. In nature, chlorine exists in two isotopes: chlorine–35 and chlorine–37, which have 76% and 24% abundance respectively. An artificially created isotope, chlorine-36 has a half-life of about 300,000 years, has radioactivity, and has importance in ongoing research.
Typically, chlorine remains in its diatomic state, Cl2. It has seven valence electrons, so it needs just one electron to complete its octet, hence its high reactivity. Importantly, while fluorine is the most electronegative element, chlorine actually has a higher electron affinity. This means chlorine is more likely to form negative ions than its halogen cousin fluorine. This makes chlorine a chief oxidizer, as it readily removes electrons from other atoms. Being a good oxidizing agent is the magic behind many of its real-world applications.
Chlorine Element Compounds:
Dichlorine Monoxide (Cl2O) – Yellow gas generated by passing chlorine over mercuric oxide. The anhydride of hypochlorous acid, it condenses into a liquid at 4°C.
Dichlorine Heptoxide (Cl2O7) – A transargonic chlorine oxide with a melting point of -91°C. Boiling point 82°C. Made by mixing tetra phosphorus decoxide (P4O10) with perchloric acid (HClO4).
Perchloric acid (HClO4) – A mineral acid typically found as an aqueous solution. Highly corrosive to metals and tissue. Clear and odorless. Perchloric acid or rupture its surrounding container if exposed to heat for a prolonged period.
Hydrochloric acid (HCl) – also known as muriatic acid, HCl is a pungent, colorless solution. It has strong acidity and serves as the main acid used by the human stomach during digestion.
Sodium Hypochlorite (NaClO) – made by electrolysis of sodium chloride solution, this compound is notorious for being a household sterilizing and bleaching agent. The hypochlorite ion is an excellent oxidizer.
Hypochlorous Acid (HClO) – a weak acid created by adding a strong acid to a solution of hypochlorite ions
Physical Properties of Chlorine:
Boiling Point: -34.04°C
Density: 1.562 g/cm3
Atomic Mass: 35.43 u
Electronegativity (Pauling Scale): 3.16
Classification: Non-metal, halogen family
Crust Abundance: 0.017%
Key Isotopes: Cl-35, Cl-37
Electron Configuration (Noble gas notation): [Ne]3s23p5
Toxicity: Highly toxic
Specific Gravity: 1.41
Isolation of Chlorine
Generally, chlorine is isolated by the electrolysis of natural minerals. Chemists call the process of brine electrolysis “the chloralkali process”. Further, this involves one of three types of cells: mercury cells, diaphragm cells, or membrane cells.
Where can I buy Elemental Chlorine?
Chemical retailers sell many easily found chlorine products. A cheaper way to obtain chlorine is through pool chemicals, but this is often in the form of an acid.