Chalcogen

The chalcogens are the chemical elements in group 16 of the periodic table. This group is also called the oxygen family. It includes oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the radioactive elements polonium (Po) and livermorium (Lv). The name "chalcogen" means "ore-forming" because early scientists noticed these elements were important in forming ores.

Sulfur has been known since ancient times, and oxygen was identified as an element in the 18th century. Selenium, tellurium, and polonium were discovered in the 19th century, while livermorium was made in the year 2000. All chalcogens have six valence electrons, which means they are two electrons short of a full outer shell. This affects how they react with other elements.

These elements play important roles in nature and our lives. Selenium is a nutrient but can be toxic in large amounts. Tellurium can have unpleasant effects, though some organisms can use it. Polonium is always harmful because of its radioactivity. Oxygen is used mainly in steelmaking, sulfur is turned into sulfuric acid for the chemical industry, and selenium is important for making glass. Tellurium is used in things like optical disks and solar cells.

Properties

Chalcogens are elements found in group 16 of the periodic table. They include oxygen, sulfur, selenium, tellurium, polonium, and livermorium. These elements share similar patterns in their electron arrangements, especially in their outer shells, which gives them similar chemical behaviors.

All chalcogens have six valence electrons. Solid, stable chalcogens are usually soft and do not conduct heat well. As you move to chalcogens with higher atomic numbers, their density, melting and boiling points, and atomic and ionic sizes tend to increase.

Different forms of these elements, known as allotropes, exist. For example, oxygen has diatomic oxygen (O₂) and ozone (O₃). Sulfur has over 20 known allotropes, including rhombic sulfur and monoclinic sulfur. Selenium has several allotropes, such as the gray "metallic" form and red and black forms. Tellurium’s typical form is hexagonal, and polonium has two allotropes.

Oxygen, sulfur, and selenium are nonmetals, while tellurium is a metalloid, meaning its properties are between metals and nonmetals. Polonium’s classification is uncertain, but it may be a metalloid. Oxygen behaves differently from the other chalcogens due to its higher electronegativity and lack of vacant d-orbitals.

Chalcogens can form compounds in various oxidation states. Oxygen commonly forms compounds in the -2 state, while sulfur, selenium, and tellurium can have oxidation states of -2, +4, and +6. These elements form many acids and ions, such as sulfates, selenides, and tellurides, and are found in minerals like pyrite.

Compounds

With halogens

Chalcogens make compounds with halogens called chalcohalides or chalcogen halides. Many of these are well-known and used in chemistry. Some more complex ones, like sulfenyl and sulfonyl halides, are less known. There are different numbers of known compounds for each halogen: 13 with fluorine, 9 with chlorine, 8 with bromine, and 6 with iodine. Some heavier chalcogen halides interact strongly with other molecules. For example, sulfur hexafluoride is stable and well-known, while some lower-valence sulfur fluorides are less stable. Certain selenium and tellurium compounds also have known structures.

Organic

Alcohols and similar compounds contain oxygen. In thiols, selenols, and tellurols, sulfur, selenium, and tellurium take the place of oxygen. Thiols are better known than selenols or tellurols. Some organic sulfur compounds can smell very bad. There are also compounds like thioethers, selenoethers, and telluroethers. Some of these are used in industry.

With metals

There are many compounds where metals bond with chalcogens. Some include alkali metals and transition metals. Certain rare earth metals also form bonds with chalcogens. These compounds can have unique structures and properties. Some metal chalcogenides might help in making tiny particles more stable.

With pnictogens

Chalcogens bond with phosphorus and other pnictogens like arsenic and antimony. These bonds have been studied for over 200 years and are used in things like insecticides and matches. Many such compounds have been discovered, though fewer are known for tellurium. Some of these compounds can form long chains or rings.

Other

Chalcogens can bond with elements from the carbon group, such as silicon and tin. They also form hydrides, though some like tellurium hydride are unstable. Chalcogens form oxides and sulfides, like sulfur dioxide and selenium sulfide, which is used in some shampoos. Some boron compounds also include chalcogens, mostly sulfur.

History

Early discoveries

Sulfur has been known since ancient times and is mentioned in the Bible fifteen times. It was known to the ancient Greeks and commonly mined by the ancient Romans. In the Middle Ages, it was a key part of alchemical experiments. In the 1700s and 1800s, scientists Joseph Louis Gay-Lussac and Louis-Jacques Thénard proved sulfur to be a chemical element.

Early attempts to separate oxygen from air were hampered by the fact that air was thought of as a single element up to the 17th and 18th centuries. Robert Hooke, Mikhail Lomonosov, Ole Borch, and Pierre Bayden all successfully created oxygen, but did not realize it at the time. Oxygen was discovered by Joseph Priestley in 1774 when he focused sunlight on a sample of mercuric oxide and collected the resulting gas. Carl Wilhelm Scheele had also created oxygen in 1771 by the same method, but Scheele did not publish his results until 1777.

Tellurium was first discovered in 1783 by Franz Joseph Müller von Reichenstein. He discovered tellurium in a sample of what is now known as calaverite. Müller assumed at first that the sample was pure antimony, but tests he ran on the sample did not agree with this. Muller then guessed that the sample was bismuth sulfide, but tests confirmed that the sample was not that. For some years, Muller pondered the problem. Eventually he realized that the sample was gold bonded with an unknown element. In 1796, Müller sent part of the sample to the German chemist Martin Klaproth, who purified the undiscovered element. Klaproth decided to call the element tellurium after the Latin word for earth.

Selenium was discovered in 1817 by Jöns Jacob Berzelius. Berzelius noticed a reddish-brown sediment at a sulfuric acid manufacturing plant. The sample was thought to contain arsenic. Berzelius initially thought that the sediment contained tellurium, but came to realize that it also contained a new element, which he named selenium after the Greek moon goddess Selene.

Periodic table placing

Three of the chalcogens (sulfur, selenium, and tellurium) were part of the discovery of periodicity, as they are among a series of triads of elements in the same group that were noted by Johann Wolfgang Döbereiner as having similar properties. Around 1865 John Newlands produced a series of papers where he listed the elements in order of increasing atomic weight and similar physical and chemical properties that recurred at intervals of eight; he likened such periodicity to the octaves of music. His version included a "group b" consisting of oxygen, sulfur, selenium, tellurium, and osmium.

After 1869, Dmitri Mendeleev proposed his periodic table placing oxygen at the top of "group VI" above sulfur, selenium, and tellurium. Chromium, molybdenum, tungsten, and uranium were sometimes included in this group, but they would be later rearranged as part of group VIB; uranium would later be moved to the actinide series. Oxygen, along with sulfur, selenium, tellurium, and later polonium would be grouped in group VIA, until the group's name was changed to group 16 in 1988.

Modern discoveries

In the late 19th century, Marie Curie and Pierre Curie discovered that a sample of pitchblende was emitting four times as much radioactivity as could be explained by the presence of uranium alone. The Curies gathered several tons of pitchblende and refined it for several months until they had a pure sample of polonium. The discovery officially took place in 1898. Prior to the invention of particle accelerators, the only way to produce polonium was to extract it over several months from uranium ore.

The first attempt at creating livermorium was from 1976 to 1977 at the LBNL, who bombarded curium-248 with calcium-48, but were not successful. After several failed attempts in 1977, 1998, and 1999 by research groups in Russia, Germany, and the US, livermorium was created successfully in 2000 at the Joint Institute for Nuclear Research by bombarding curium-248 atoms with calcium-48 atoms. The element was known as ununhexium until it was officially named livermorium in 2012.

Names and etymology

In the 19th century, Jons Jacob Berzelius suggested calling the elements in group 16 "amphigens", as the elements in the group formed amphid salts (salts of oxyacids, formerly regarded as composed of two oxides, an acid and a basic oxide). The term received some use in the early 1800s but is now obsolete. The name chalcogen comes from the Greek words χαλκος (chalkos, most narrowly "copper", but the term was also used for bronze, brass, any metal in the poetic sense, ore, and coin), and γενές (genes, born, gender, kindle, produce). It was first used in 1932 by Wilhelm Biltz's group at Leibniz University Hannover, where it was proposed by Werner Fischer. The word "chalcogen" gained popularity in Germany during the 1930s because the term was analogous to "halogen". Although the literal meanings of the modern Greek words imply that chalcogen means "copper-former", this is misleading because the chalcogens have nothing to do with copper in particular. "Ore-former" has been suggested as a better translation, as the vast majority of metal ores are chalcogenides and the word χαλκος in ancient Greek was associated with metals and metal-bearing rock in general; copper, and its alloy bronze, was one of the first metals to be used by humans.

Oxygen's name comes from the Greek words oxy genes, meaning "acid-forming". Sulfur's name comes from either the Latin word sulfurium or the Sanskrit word sulvere; both of those terms are ancient words for sulfur. Selenium is named after the Greek goddess of the moon, Selene, to match the previously discovered element tellurium, whose name comes from the Latin word telus, meaning earth. Polonium is named after Marie Curie's country of birth, Poland. Livermorium is named for the Lawrence Livermore National Laboratory.

Occurrence

The four lightest chalcogens—oxygen, sulfur, selenium, and tellurium—are found naturally on Earth. Sulfur and oxygen are part of copper ores, while selenium and tellurium are found in tiny amounts in these ores. Polonium forms from the decay of other elements, but it is not found naturally in large amounts. Livermorium does not occur naturally at all.

Oxygen is very common. It makes up 21% of the air we breathe, 89% of water, 46% of the Earth's crust, and 65% of the human body. Stars much bigger than our Sun create oxygen in their cores. Sulfur is also found in soil, water, and the air, and it is a part of many minerals. Selenium and tellurium are much less common on Earth but are still found in small amounts in soil, water, and some minerals. Polonium is very rare and only found in tiny traces. Livermorium can only be made in science labs.

Chalcophile elements

Chalcophile elements are those that stay close to Earth's surface because they easily combine with chalcogens, especially sulfur, to form compounds. These elements do not mix well with oxygen and prefer to bond with sulfur. Because of this, they ended up separated from other elements when Earth's crust formed. This makes them less common in the Earth's crust than they are in space, but not as rare as some other elements.

See also: Chalcophile and Goldschmidt classification

Production

Each year, about 100 million metric tons of oxygen are made. The most common way to get oxygen is by cooling air until it becomes a liquid and then warming it up. This process lets all other gases escape, leaving mostly oxygen behind. Another way to get oxygen is by passing air through special materials that absorb other gases, leaving oxygen.

Sulfur used to be mined directly from the ground, but today it is more often taken from oil, natural gas, and tar. Selenium is produced in small amounts each year, mostly from waste materials left over from refining copper. Tellurium is a by-product made while processing copper. Polonium is made in special reactors by bombarding certain materials with neutrons. Livermorium is created in labs by smashing tiny particles together, and only a very small amount has ever been made.

Applications

Oxygen is very important for living things because it helps with how our bodies work. We also use oxygen in making steel, creating chemicals, treating water, and even as part of rocket fuel.

Sulfur is used to make important chemicals like sulfuric acid. It is also part of mixtures that make rubber stronger and is used in making fireworks and treating soil. Selenium is mainly used to make glass and metals, and it helps in farming and electronics too. Tellurium is used in computer parts and solar panels. Polonium, because it gives off special kinds of energy, is used in research and some batteries, but it is rare and not used much. Livermorium is too rare to have any uses right now. Chalcogens, the group of elements this belongs to, help in making tiny parts for computers and studying how molecules connect and change.

Biological role

Main articles: Dioxygen in biological reactions, Sulfur cycle, and Selenium in biology

Oxygen is very important for almost all living things because it helps make energy. It is also part of many things in our bodies, like water, the building blocks of proteins, and DNA. Our blood and bones contain a lot of oxygen.

All animals need sulfur, which is found in some proteins. Plants take sulfur from the soil, and it helps metals move in our bodies. We get about 900 milligrams of sulfur each day. Some sulfur compounds smell very strong.

Animals and some plants need small amounts of selenium for certain enzymes. We usually get between 6 and 200 micrograms of selenium each day from foods like mushrooms and brazil nuts. Selenium can help protect us from harmful metals.

Tellurium is not known to be needed for animal life, but some tiny organisms use it. We get small amounts of tellurium from food and the environment.

Polonium does not play a role in living things and is very harmful because it is radioactive.

Toxicity

Oxygen is usually safe, but using it in very high amounts can be harmful. Pure oxygen can be risky for sports divers at deep underwater depths, and ozone, another form of oxygen, can hurt the breathing system.

Sulfur is normally harmless and even helpful for our bodies, but too much of it can irritate the eyes, skin, and lungs. Some sulfur compounds, like hydrogen sulfide and sulfur dioxide, can be very harmful.

Selenium is needed in tiny amounts by our bodies, but too much can cause bad breath and body smells. Long-term exposure can lead to weight loss, tiredness in making red blood cells, and skin problems.

Tellurium can make breath smell bad and cause stomach problems if eaten in small amounts. Larger amounts can make people very sick.

Polonium is very dangerous if swallowed or breathed in, and it can harm the body seriously.

Amphid salts

Long ago, a scientist named Jons Jacob Berzelius called certain chemical salts "amphid salts." These salts came from elements in the 16th group of the periodic table, like oxygen, sulfur, selenium, and tellurium. People used this name in the early 1800s, but we don't use it anymore. Today, we call these elements chalcogens.