Oxygen is a highly reactive non-metal and is one of the most significant elements present on the Earth. It is widely used in various manufacturing processes and is the element that sustains the life.

 Discovery and History

The discovery of element as a unique element dates to 2nd century when Philo observed the association of process of combustion with presence of air. Robert Hook, in 1665 proposed the presence of unique substance in air that is released when potassium nitrate is heated. Later, John Mayow (1668) proposed that there is a certain element termed as “nitoarial spirit” (for oxygen) present in air that is consumed in combustion and respiration. In 1774, Carl Wilhelm Scheele and Joseph Priestley independently discovered oxygen, and named it “fire air” and “dephlogisticated air”, respectively due to its role in combustion. The name oxygen originates from combination of two words, oxys and genes, that are Greek word for “acid forming”. The name was first proposed by Antoine Lavoisier [1].


Periodic Table ClassificationGroup 16
Period 2
State at 20CGas
ColorColorless gas
Electron Configuration[He] 2s2 2p4
Electron Number8
Proton Number8
Electron Shell2, 6
Density1.43 g.cm-3 at 20°C
Atomic number8
Atomic Mass15.99 g.mol -1
Electronegativity according to Pauling3.44


Oxygen is considered as the most abundant element in the biosphere of Earth, by mass. Biosphere involves the land, sea and air that support life. Oxygen constitutes around 49.2% of Earth’s crust [2]. Oxygen is the third most abundant element in the Universe. The most common allotrope of elemental oxygen is dioxygen O2. It is primarily present in the atmosphere of the Earth and is a major part of gaseous content of the biosphere. Oxygen is the 2nd most abundant component of Earth’s atmosphere (present in about million billion tons or 21% of earth’s atmosphere). Another allotrope of oxygen, known as ozone, is a trioxygen molecule. Ozone is present in the upper atmosphere and provides protection against harmful UV rays form sun by absorbing them. Oxygen is a major component of the water bodies on Earth and constitutes around 88.8% by mass of oceans [3]. The production of free oxygen on Earth started around 3.5 billion years ago and lead to a gradual increase over the centuries. The aerobic environment and the significantly high concentration of oxygen on earth is attributed to the oxygen cycle. Oxygen is continuously replenished into the Earth’s environment, by the outstanding process of photosynthesis (a process by which light energy from sun splits water molecule to release free oxygen). Elemental or free oxygen is present in solution form in water bodies, where it plays crucial role in providing support to ocean life. About 45-70% of environmental oxygen content is provided by green algae and cyanobacteria, while rest is contributed by the terrestrial plants [4]. Cellular respiration is a vital energy production phenomenon that occurs in all plants and animals, and lead to oxygen consumption while photosynthesis continuously replenish the oxygen being consumed.

Physical Properties

Oxygen is a colorless, tasteless and odorless gas. It readily dissolves in water, and more conveniently in freshwater as compared to seawater. The freezing point of oxygen is −218.79 °C, and it condenses at −182.95 °C. Oxygen, in both of its liquid and solid state, appear as clear, sky-blue color compound. Oxygen is highly combustible element but not flammable. It only helps in burning but does not burn itself.  Oxygen is a poor conductor of electricity and heat. Oxygen is denser than air (1.429 grams per liter) [5].

Chemical Properties

Oxygen is a very reactive element. Oxygen has an oxidation state of -2 in almost all compounds. While -1 is present in some peroxides [6]. The most common compound of oxygen is water, which is an oxide of hydrogen. Oxygen has a high electronegativity. Oxygen is also present in the form of carbon dioxide in trace amount in the atmosphere. Oxygen compounds including various silicates (silicon-oxygen mineral) are abundantly present in the mantle and crust of the Earth. Oxygen also reacts with transition metals and form dioxygen complexes with them, such as myoglobin and hemoglobin (oxygen carrying proteins present in the blood). Various significant organic compounds also contain oxygen, including citric acid glycerol, acetic anhydride and acetamide. The most common reaction of oxygen is termed as oxidation. Ozone is a powerful oxidizing agent [7]

Significance and Uses

  • The most common use of oxygen is in melting, refining and manufacturing of steel and various metals.
  • It is widely used in the manufacturing of various chemicals.
  • Oxygen is widely used in making life support kits and storage for medical and recreational activities.
  • Oxygen is used in making oxyacetylene for welding.
  • It is used as oxidant in rocket propellent, by combining hydrogen with liquid oxygen.
  • It is used in purification processes of various metals.

Health Hazards

At high levels oxygen acts as a toxic gas. Prolonged exposure to high levels of oxygen present at a partial pressure of more than 50 kilopascals, can lead to various health effects, including convulsion, difficulty in breathing and unconsciousness. The use of oxygen incubators for premature babies have been ceased due to toxic effect of high oxygen levels that led to blindness. Oxygen helps combustion, so concentrated sources of oxygen can be a potential risk of explosion or fire.

Isotopes of Oxygen

There are three isotopes in naturally occurring oxygen: oxygen-16, oxygen, -17 and oxygen-18. These are stable isotopes of oxygen and oxygen-16 is the most abundant of all isotopes with a natural abundance of 99.76%. There are fourteen radioactive isotopes of oxygen [8].




 [1]. Mary Elvira Weeks, The discovery of the elements. IV. Three important gases., J. Chem. Educ., 1932, 9 (2), p 215

[2]. “Oxygen”. Los Alamos National Laboratory. Archived from the original on October 26, 2007. Retrieved December 16, 2007.

[3]. Cook & Lauer 1968, p. 500

[4]. Fenical, William (September 1983). “Marine Plants: A Unique and Unexplored Resource”. Plants: the potentials for extracting protein, medicines, and other useful chemicals (workshop proceedings). DIANE Publishing. p. 147. ISBN 978-1-4289-2397-3.

[5]. “Oxygen Facts”. Science Kids. February 6, 2015. Retrieved November 14, 2015.

[6]. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9., p. 28

[7]. http://www.elementalmatter.info/oxygen-properties.htm

[8]. Oxygen Nuclides / Isotopes”. EnvironmentalChemistry.com. Retrieved December 17, 2007.



Chromium is a transition metal that was discovered by Gottlob Lehmann in 1766. It has a shiny surface that is resistant to corrosion and this quality makes its ideal for manufacturing and coating of wide range of material, including cars and bikes.

History and Discovery

Chromium was initially discovered in red crystalline mineral form, known Siberian red lead, by Johann Gottlob Lehmann (1766). Later, chromium was discovered as a novel, and isolated metal by Louis-Nicolas Vauquelin in 1797. The name chromium has been derived from Greek word, chroma, which means color. The name was given to this metal as it exists in diverse colors and was suggested by, Antoine Francois de Fourcroy (1755-1809) and René-Just Haüy (1743-1822). Chromium has a distinct shine and forms various compounds in different colors that include green, purple, black, yellow, and orange [1].



Periodic Table ClassificationGroup 6
Period 4
State at 20CSolid
ColorSilvery metallic
Electron Configuration[Ar] 3d5 4s1
Electron Number24
Proton Number24
Electron Shell2, 8, 13, 1
Density7.19 g.cm-3 at 20°C
Atomic number24
Atomic Mass51.99 g.mol -1
Electronegativity according to Pauling1.66


Chromium is the 13th most abundant element in the Earth’s crust [2]. Chromium is not present in free form. It is present in form of various ores, and the most common ore is iron chromium oxide FeCr 2 O4, which is termed as chromite. Chromite is the principal source of chromium that is used in pigments, worldwide. Chromium is released in the environment by erosion of rocks that contain chromium. Volcanic activities also play important role in the distribution of chromium. The largest producer of chromite is South Africa, followed by India, Brazil, Turkey, Finland and Kazakhstan [3]. Russia has deposits of the rare native form of chromium in Udachnaya Pipe, from which native chromium and diamonds are extracted. The annual production of chromite is about 28.8 million metric tons, which is primarily being used in the production of steel.

Physical Characteristics

Chromium is steel-gray in color. It is shiny, hard and brittle metal, that is easy to break. The density of chromium is 7.1 g.cm-3. Chromium has a highly polishable texture. It is resistant to tarnishing upon exposure with air. Chromium has outstanding magnetic properties. It is very dense metal and has a thermal conductivity of 93.9 W [4].

Chemical Characteristics

Chromium form variety of compounds and exists in many oxidation states, including +3, +6, +1. +4 and +5. The predominant and most stable oxidation state of chromium is +3 [5]. Large number of chromium [III] compounds are present, such as compound of chromium with sulfuric and hydrochloric acid. Chromium (VI) compounds, including chromate anion (CrO42-), are powerful oxidizing agents.

Significance and Use

  • The widest usage of chromium is in the making of metal alloys. Chromium can impart strength corrosion resistance and shine to various metals and is widely used in the manufacturing of steel.
  • Chromium is widely used as coating agent, as it is highly durable and strong as compared to other metals. Chromium plating is used for bikes and cars.
  • Chromium has been widely used in the manufacturing of dyes, pigments and paints due to its unique and wide range of colors.
  • Chromium oxides are used for dying glass and ceramics. It imparts natural green color and is also used by armed forces to paint their tanks and vehicles to imitate infrared reflectance of green leaves and give them camouflage.
  • Chromium is widely used for tanning of leather. Chromium has the ability to cross link the collagen fibers of leather and provide stability.
  • Chromium is used in the making of blast furnace, kilns, brick mold and sand in foundry for casting of metals.
  • Chromium compounds (with acids) are used for cleaning purposes due to their oxidizing properties.

Health Hazards

Chromium has a significant role in the body of living organisms. In humans, chromium plays crucial role in the metabolism of sugar in the body. Chromium deficiency is also linked with diabetes by affecting the function of insulin (a hormone that plays important role in the metabolism of sugar, proteins and fat) [6]. In contrast, Cr (VI) is highly toxic compound. It can lead to mutagenic effect and lung damaging effects if inhaled. If Cr (VI) is ingested in contaminated water, it can lead to various stomach complications, including tumors. The range of oral toxicity concentration is 50 to 150 mg/kg of Cr (VI). Skin contact with hexavalent chromium can aggravate allergic reaction termed as allergic contact dermatitis [7]. Chromium can enter our body through food cooked in stainless steel pots. Chromium (III) is also considered toxic and have mutagenic effects on DNA [8]. Large amounts of chromium compounds are being released into environment by various industries, tanneries (paints, dyes, leather manufacturing), and pose threat of contamination of soil and water.

 Isotopes of Chromium

Natural chromium has four isotopes: chromium-50, chromium-52, chromium-53, chromium-54. There are twenty-one other isotopes of chromium. Chromium-53 is the most abundant among all isotopes. Several isotopes of chromium are used for medical purposes. For instance, chromium-51 is used for studying survival and growth of red blood cells and for measuring blood volume [9].




[1]. Per Enghag, Encyclopedia of the elements: technical data, history, processing, applications.,p 577- 578, John Wiley and Sons, 2004

[2]. Emsley, John (2001). “Chromium”. Nature’s Building Blocks: An A-Z Guide to the Elements. Oxford, England, UK: Oxford University Press. pp. 495–498. ISBN 978-0-19-850340-8.

[3]. Papp, John F. “Mineral Yearbook 2015: Chromium” (PDF). United States Geological Survey. Retrieved 2015-06-03.

[4]. http://www.chemistryexplained.com/elements/A-C/Chromium.html

[5]. Clark, Jim. “Oxidation states (oxidation numbers)”. Chemguide. Retrieved 3 October 2018

[6] Chromium”. Office of Dietary Supplements, US National Institutes of Health. 2016. Retrieved 26 June 2016.

[7]. “ToxFAQs: Chromium”. Agency for Toxic Substances & Disease Registry, Centers for Disease Control and Prevention. February 2001. Archived from the original on 2014-07-08. Retrieved 2007-10-02.

[8]. Eastmond, David A.; MacGregor, J. T.; Slesinski, R. S. (2008). “Trivalent Chromium: Assessing the Genotoxic Risk of an Essential Trace Element and Widely Used Human and Animal Nutritional Supplement”. Critical Reviews in Toxicology. 38 (3): 173–190. doi:10.1080/10408440701845401. PMID 18324515.

[9]. Naturally occurring isotope abundances: Commission on Atomic Weights and Isotopic Abundances report for the International Union of Pure and Applied Chemistry in Isotopic Compositions of the Elements 1989, Pure and Applied Chemistry, 1998, 70, 217. [Copyright 1998 IUPAC]


Gold is a precious metal which has been in human use since 2000 BC. It is unreactive and is highly resistant to corrosion which makes it favorable for wide range of medicinal, ornamental and structural use.

History and Discovery

Gold is the metal of prehistoric times and it was collected from water streams in form of particles. The Egyptians in around 2000 BC started mining of gold. And gold made items, such as masks, graves etc. have been found to contain gold from civilization of 3800 to 2000 BC. Pure gold has been found from around 6000 years ago Israel kingdom [1]. Gold coins were made in the reign of King Croesus of Lydia (modern Turkey) (561-547 BC).  Gold has been considered as perfect and precious metal since ancient times, and long relentless but in vain efforts have been made over centuries to transform various metals into gold, a concept known as alchemy. The word gold has been originated from the word “geolo” used by Anglo-Saxon civilization that inhabited England in the 5th century. Geolo (Sanskrit origin meaning to shine) means yellow. The symbol of gold comes from a word of Latin origin, aurum, which is originated from Aurora, which is the goddess of morning glow [2].


Periodic Table ClassificationGroup 11
Period 6
State at 20CSolid
ColorMetallic yellow
Electron Configuration[Xe] 4f14 5d10 6s1
Electron Number79
Proton Number79
Electron Shell2, 8, 18, 32, 18, 1
Density19.32 g.cm-3 at 20°C
Atomic number79
Atomic Mass196.97 g.mol -1
Electronegativity according to Pauling2.54


Gold is widely present in the Earth’s crust (0.3 ppm by weight). It is also present in river beds as rock bound gold is released by erosion of rock by running water. Gold also exists in the form of alloy, such as amalgam (with mercury) or with silver. Gold is found in association of pyrites deposits and from quarts and gravels.  Naturally, most of the gold present in the Earth’s crust is in combination with silver. The term “electrum” is used for gold ore that have silver content of more than 20%. The biggest producer of gold is China from around two third of the gold (around 455 tons) in world is produced. The other countries where gold is being mined include USA, Canada and Russia. The annual production of gold in the world is 2500 tons per year. Oceans, including the Northeast Pacific and Atlantic contain about 10–30 parts per quadrillion, that makes about 10–30 g/km3 of gold in form of flakes or nuggets [3].

Physical Characteristics

Gold is a reddish yellow metal. It is highly ductile and malleable. Gold is a soft metal and is usually used in alloyed form to provide strength and durability. About 1 ounce of gold can be hammered or pressed into 300 square feet sheet. The unit carat is used for the percent purity of gold, especially in jewellery. Twenty-four carats gold is considered as pure gold. Gold has the ability to conduct heat and electricity with great efficiency. And is considered as a fairly dense metal with density of 19.32 g/cm3 [4].

Chemical Characteristics

Gold is an inert metal and considered as the most noble metal. However, these are many diverse forms of gold, with oxidation number ranging from -1 to +5. The dominant form of gold is Au(I) and Au (III). Gold is resistant to attack by oxygen at any temperature. Gold is unreactive and resistant to most acids. It can dissolve in a mixture of hydrochloric acid and nitric acid, known as aqua regia. Gold is also soluble in alkaline solutions of cyanide. Gold forms amalgam with mercury but it does not involve a chemical reaction. Gold is highly resistant to corrosion. Gold can react with certain halogens, such as fluorine to form gold (III) fluoride. Gold in powdered form can react with chlorine to form gold chloride. Various alloys of gold are formed to alter the strength and hardness of gold and create exotic colors [5].

Uses and Significance

  • Gold is a precious metal and widely used in making of jewellery, coinage, crowns and decorative items.
  • It is widely used in making components of computerized devices, such as corrosion resistant electrical conductors.
  • Gold is used in the glass industry for making colored-glass.
  • It is used as fillers in tooth restoration.
  • Certain salts of gold are used for medicinal purpose.
  • Flakes of gold are used in various drinks and sweets.
  • Gold plating is used in helmets used by astronauts as gold due to its inert nature can provide protection against dangerous and harmful effects of solar radiations.
  • Radioactive isotope of gold (Au-198) has been used to treat various cancers including prostate and bladder.

Health Hazard

Gold is a non-toxic metal. It may cause irritation in eye or skin and prolonged exposure can lead to irritation in lungs. There is no ecotoxicity of gold as it is insoluble in water. Gold is used for therapeutic purpose in a treatment called Chrysoteraphy, for relieving pain in rheumatoid arthritis. Recently, gold particles based anti-cancer drugs have been investigated.

Isotopes of Gold

There are 35 isotopes of gold, with mass numbers ranging from 171 to 205. These are the artificially produced isotopes of gold. The natural gold consists of one stable isotope, Au-197, which is the only stable isotope. The isotopes with atomic masses above 197 decay by emission of β rays [6].



[1]. Gopher, A.; Tsuk, T.; Shalev, S. & Gophna, R. (August–October 1990). “Earliest Gold Artifacts in the Levant”. Current Anthropology. 31 (4): 436–443. doi:10.1086/203868. JSTOR 2743275.

[2]. Eric. J. Holmyard, Makers of Chemistry., 1931, Oxford at the Clarendon Press. p163

[3]. Kenison Falkner, K.; Edmond, J. (1990). “Gold in seawater”. Earth and Planetary Science Letters. 98 (2): 208–221. Bibcode:1990E&PSL..98..208K. doi:10.1016/0012-821X(90)90060-B.

[4]. https://www.webelements.com/gold/physics.html

[5]. https://sciencestruck.com/chemical-properties-of-gold

[6]. “Nudat 2”. National Nuclear Data Center. Retrieved 12 April 2012



 Hydrogen is one of the three most abundant elements present on Earth. It was discovered in 1766 by Henry Cavendish and is widely used for various industrial, medical and recreational purposes.

Discovery and History

The informal discovery of hydrogen dates to 1500s when Paracelsus (alchemist) observed the production of bubbles (gas) when sulfuric acid was added to iron and later Robert Boyle (1671) observed the production of same flammable bubbles. But the formal discovery of hydrogen was reported by Henry Cavendish (1766), who analyzed the bubbles and showed that burning of hydrogen lead to the production of water. Hence the gas was named hydro-genes (1783 by Antoine Lavoisier), which is the Greek word for “water-former”. In 1898, James Dewar successfully liquified hydrogen [1]. In as early as 1783, hydrogen gas was used in air balloons by Jacques Charles, which demonstrated the power and reliability of hydrogen for providing the lift for air-travel. And later, Henri Giffard (1852), made the first hydrogen-lifted airship. Hydrogen-lifted airships found tremendous usage in the World War 1, where they were used for transferring people, as observation platforms and as bombers. Hydrogen also has a notorious event related to its name, the incident of Hindenburg airship (1937), were combustion of hydrogen led to the destruction of the ship in the midair and brought an end to the era of hydrogen-based air-travels [2].


Periodic Table ClassificationGroup 1
Period 1
State at 20CGas
ColorColorless gas
Electron Configuration1s1
Electron Number1
Proton Number1
Electron Shell1
Density0.09 g.cm-3 at 20°C
Atomic number1
Atomic Mass1.01 g.mol -1
Electronegativity according to Pauling2.20


Hydrogen is ubiquitous in nature as it is present in water. It is considered as the 3rd most abundant element in the Earth’s atmosphere and the most abundant element in the universe. Hydrogen is the main component of living systems (hydrocarbons). [3]. Hydrogen is found in significant abundance in undetected form of mass, such as dark matter, and in gas giant planets and stars. In gaseous form, it is present only in a small fraction and makes around 1 part per million in volume.  Hydrogen is mostly present in its atomic and plasma states, which have significantly different properties as compared to the molecular (gaseous) form. In its plasma form, hydrogen give rise to natural phenomenon of Birkeland currents and aurora (by interacting with magnetosphere of the Earth). The neutral atomic state of hydrogen is mainly present in the interstellar medium ISM (outer space) [4].

 Physical Characteristics

Hydrogen gas is the lightest of all gases. It has the lowest density (0.0899*10 -3 g.cm -3 at 20 °C) as compared to all other gases. Hydrogen is odorless and colorless gas. It is non-toxic and nonmetallic at standard conditions (standard temperature and pressure). Hydrogen has an atomic number of 1 and atomic mass of 1.007825g.mol-1. It has a boiling point of -252.8C and a melting point of -259.2 C.

 Chemical Characteristics

Hydrogen is a highly (combustible) flammable gas. Hydrogen is more soluble in organic solvents and less soluble in water. At room temperature, hydrogen is stable and unreactive. However, under different environmental conditions, various metals absorb hydrogen, such as the absorption of hydrogen by steel can cause brittleness in steel [5]. Hydrogen becomes highly reactive at higher temperatures. And lead to the dissociation of its diatomic form into free atom of hydrogen, which is highly reactive and a powerful reducing agent. Free hydrogen radical can react with chlorides and oxides of various metals to form free metals. It can lead to the formation of hydrides of various metals, non-metals such as, H2S, NAH, PH3 and KH. One of the most common compounds produced by elemental hydrogen is hydrogen peroxide (H2O2) with oxygen. The light atomic nature of hydrogen impart various favorable properties to it, including low viscosity, and high thermal conductivity and specific heat as compared to all other gases.

Significance and Uses

  • Hydrogen is widely used to produce ammonia.
  • The reaction of combination of hydrogen atoms is quite exothermic. And this heat is used in atomic hydrogen welding process.
  • Hydrogen is widely used for the catalytic hydrogenation process, which is used in the production of vegetable ghee from vegetable oil (unsaturated fats to saturated fats).
  • Hydrogen is becoming popular as green fuel (clean fuel, with no emission of carbon dioxide or other toxic compounds). Various fuel cells are being manufactured for making internal combustion engines for making pollution free buses and cars.
  • Hydrogen is used as rocket fuel and as rocket propellent.
  • Hydrogen provides protective and stable atmosphere for the production of flat glass sheets in glass industry.
  • It is used in electronic industry for the manufacturing of silicon chips (as flushing gas).
  • Hydrogen is widely used in power stations as a coolant in generators.

Health Effects of Hydrogen Gas

Hydrogen is toxic to the body and can absorbed by inhalation which can lead to oxygen deficiency in the body. affected individuals lead to hypoxia and show symptoms such as headaches, dizziness, ringing in ears, nausea, vomiting and unconsciousness. If untreated, victim can turn blue and it can be fatal. When hydrogen is exposed to air, it can lead to formation of explosive mixtures. Heating of hydrogen can also cause violent combustion or explosion [7].

Isotopes of Hydrogen

There are three naturally occurring isotopes of hydrogen, named 1H (protium), 2H (deuterium), and 3H (tritium). Protium is the most abundant hydrogen isotope (99.98%). Tritium is the most stable radioisotope and have a half-life of 12.32 years. All heavier isotopes of hydrogen are synthetic and are extremely unstable. Deuterium has found major applications in nuclear magnetic resonance studies [6].




[1]. Presenter: Professor Jim Al-Khalili (21 January 2010). “Discovering the Elements”. Chemistry: A Volatile History. 25:40 minutes in. BBC. BBC Four.

[2]. Emsley, John (2001). Nature’s Building Blocks. Oxford: Oxford University Press. pp. 183–191. ISBN 978-0-19-850341-5.

[3]. Miessler, G. L.; Tarr, D. A. (2003). Inorganic Chemistry (3rd ed.). Prentice Hall. ISBN 978-0-13-035471-6

[4]. Gagnon, S. “Hydrogen”. Jefferson Lab. Retrieved 5 February 2008.

[5] Rogers, H. C. (1999). “Hydrogen Embrittlement of Metals”. Science. 159 (3819): 1057–1064. Bibcode:1968Sci…159.1057R. doi:10.1126/science.159.3819.1057. PMID 17775040.

[6]. https://www.lenntech.com/periodic/elements/h.htm

[7] https://courses.lumenlearning.com/introchem/chapter/isotopes-of-hydrogen/


Zirconium is a transition metal discovered in 1789. It is a lustrous metal and is widely used in manufacturing of wide range of durable, strong and noncorrosive materials.

History and Discovery

Several zirconium related minerals, including Zircon have been mentioned in biblical writings. Zirconium was discovered by Martin Klaproth in 1789, and in 1824 Jacob Berzelius (Swedish chemist) isolated an impure form of this metal. Zirconium was isolated in pure form by Anton E. van Arkel and J.H. de Boer (1925). The name Zirconium has been originated from the Persian word zargun, that means “golden colored” [1].  Zirconium came into lime light after the 1940s, when its use in the nuclear power plants was identified.


Periodic Table ClassificationGroup 4
Period 5
State at 20CSolid
Electron Configuration[Kr] 4d2 5s2
Electron Number40
Proton Number40
Electron Shell2,8,18,10,2
Density6.49 g.cm-3 at 20°C
Atomic number40
Atomic Mass91.22 g.mol -1
Electronegativity according to Pauling1.2


Zirconium is an abundant metal. The commercial source of zirconium are the alluvial deposits present in beaches of ocean, beds of old lakes and streams. The most abundant mineral form of zirconium is baddeleyite (zirconium dioxide). The most common impurity in zirconium metal is hafnium, but for commercial use (except in nuclear reactors), zirconium with 1% hafnium is considered as pure metal. Today, the biggest producers of zirconium include South Africa, Australia, Indonesia, India, China and Sri Lanka. And around 900,000 tons per year of zircon (ZiSO4) are produced in the world [2].

Physical Characteristics

Zirconium is a grey-white element. It is shiny, lustrous, and malleable transition metal. In powder form, zirconium exists in black color. The physical characteristics of pure and impure form of zirconium greatly vary, as impure zirconium is hard and brittle, while in pure form, it is soft and ductile [3]. Zirconium is lighter than steel (have density of 6.49 g.cm-3 at 20C). The atomic number of zirconium is 40 and its atomic mass is 91.22 g.mol-1. The melting point of zirconium is 1852°C and boiling point is 4400°C. Its oxidation state is +4. It is present in the Group 4 (IV)b of the periodic table [4].

Chemical Characteristics

Zirconium is a resistant metal, with outstanding ability to withstand corrosion and heat. It can absorb significant amounts of various gases, including nitrogen, hydrogen and oxygen. Zirconium reacts vigorously with air and in divided or powder form, it can lead to spontaneous and dangerous ignition. It is unreactive with alkalis and acids and does not dissolve in them. Zirconium does not form radioactive isotopes when bombarded with neutrons [5].

Significance and Uses

  • The most common use of zirconium is in nuclear applications. It is used in the manufacturing of engineering material for nuclear reactors. For instance, zirconium based cladding fuel rods are being used and core structure of reactors is also made from zirconium. Further, zirconium does not readily absorb neutron and can withstand any mechanical damage caused from neutron bombardment in nuclear reactors.
  • Zirconium readily absorbs oxygen which makes it desirable candidate for removing residual gases from electron tubes or vacuum tubes (used in making television or computer screens).
  • Zirconium is used in making refractory materials, including crucibles, rocket launch structures, furnaces, incinerators and ovens.
  • It is used in various ceramic industries for opacification purposes (adjustment of glaze content).
  • Zirconium is used as hardening agent in making alloys, including magnesium and steel.
  • It is widely used in fabrication of valves, and pumps due to its high resistant to corrosion.
  • It is widely used in packaging and paper industry for making surface coats as zirconium have outstanding strength and resistance.

Health Hazards

Zirconium metal and its salts have low toxicity (environmental and biological) as they are scarcely soluble in water. If ingested, zirconium does not get absorbed in the tissues and passes the gut without causing any hazard. Plants also don’t absorb zirconium present in the soil. However, the radioactive isotopes zirconium 95 is a radionuclide with considerably high half-life and continue to persist in the environment and cause cancer risks for decades [5].

Isotopes of Zirconium

Zirconium have five natural isotopes, zirconium-90 (51.46 percent), zirconium-92 (17.11 percent), zirconium-91 (11.23 percent), zirconium-96 (2.80 percent) and zirconium-94 (17.40 percent). There are 28 artificial isotopes of zirconium, which range in atomic mass from 78 to 110. The zirconium-93 is the most stable artificial isotope of zirconium, while zirconium-110 is the least stable isotope (with half-life of around 30 milliseconds). 110Zr is the most radioactive isotope and the heaviest [6].



[1]. Harper, Douglas. “zircon”. Online Etymology Dictionary.

[2]. Nielsen, Ralph (2005) “Zirconium and Zirconium Compounds” in Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. doi:10.1002/14356007.a28_543

[3]. Emsley, John (2001). Nature’s Building Blocks. Oxford: Oxford University Press. pp. 506–510. ISBN 0-19-850341-5.

[4]. Lide, David R., ed. (2007–2008). “Zirconium”. CRC Handbook of Chemistry and Physics. 4. New York: CRC Press. p. 42. ISBN 978-0-8493-0488-0.

[5] https://www.lenntech.com/periodic/elements/zr.htm

[6]. https://www.britannica.com/science/zirconium