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 helped create ores.

Sulfur has been known since ancient times, and oxygen was found to be an element in the 1700s. Selenium, tellurium, and polonium were discovered in the 1800s, while livermorium was made in the year 2000. All chalcogens have six valence electrons, which means they need two more to have a full outer shell. This affects how they mix with other elements.

These elements are important in nature and our daily lives. Selenium is good for us in small amounts but can be harmful in larger amounts. Tellurium can cause unpleasant effects, but some living things can use it. Polonium is always dangerous because it is radioactive. Oxygen is mainly used in steelmaking, sulfur is used to make 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 in group 16 of the periodic table. They include oxygen, sulfur, selenium, tellurium, polonium, and livermorium. These elements have similar patterns in their electron arrangements, which makes them behave similarly in chemical reactions.

All chalcogens have six valence electrons. Solid 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.

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.

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. It is mentioned in the Bible and was used by the ancient Greeks and the ancient Romans. In the 1700s and 1800s, scientists Joseph Louis Gay-Lussac and Louis-Jacques Thénard showed that sulfur is a chemical element.

Scientists made oxygen by focusing sunlight on a sample of mercuric oxide. Joseph Priestley did this in 1774. Carl Wilhelm Scheele did the same thing earlier in 1771 but shared his findings later in 1777.

Tellurium was found in 1783 by Franz Joseph Müller von Reichenstein. He found it in a sample that looked like bismuth sulfide but was not. Later, Martin Klaproth purified it and named it tellurium after the Latin word for earth.

Selenium was found in 1817 by Jöns Jacob Berzelius. He saw a reddish-brown substance at a factory that made sulfuric acid. He thought it might be tellurium, but it was a new element. He named it selenium after the Greek moon goddess Selene.

Periodic table placing

Three chalcogens—sulfur, selenium, and tellurium—helped scientists notice patterns in elements. Around 1865, John Newlands listed elements by weight and showed that similar elements appeared every eight places. His list included oxygen, sulfur, selenium, tellurium, and osmium.

After 1869, Dmitri Mendeleev made the periodic table. He placed oxygen at the top of a group above sulfur, selenium, and tellurium. Later, Marie Curie and Pierre Curie discovered polonium.

Modern discoveries

In 1898, Marie Curie and Pierre Curie found that a sample of pitchblende gave off more radioactivity than expected. After working with a lot of pitchblende, they discovered polonium.

Livermorium was first made in 2000 at the Joint Institute for Nuclear Research by using curium and calcium. It was called ununhexium until it was named livermorium in 2012.

Names and etymology

The name chalcogen comes from Greek words meaning "ore-former". This is because many metal ores contain chalcogens. Oxygen’s name means “acid-forming”. Sulfur’s name comes from ancient words. Selenium is named after the moon goddess Selene. Polonium is named for 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 the air we breathe, water, the Earth's crust, and much of the human body. Stars create oxygen in their cores. Sulfur is found in soil, water, and the air, and it is a part of many minerals. Selenium and tellurium are less common on Earth but are still found in small amounts in soil, water, and some minerals. Polonium is very rare. Livermorium can only be made in science labs.

Chalcophile elements

Chalcophile elements 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 are less common in the Earth's crust than in space.

See also: Chalcophile and Goldschmidt classification

Production

Every year, we make about 100 million metric tons of oxygen. One way to get oxygen is by cooling air until it becomes a liquid and then warming it up. This makes the other gases go away, and we are left with mostly oxygen. Another way is to pass air through special materials that take in other gases, leaving the oxygen.

Sulfur is often taken from oil, natural gas, and tar. Selenium is made in small amounts from waste materials left over from refining copper. Tellurium is made as a by-product when we process copper. Polonium is made in special reactors. 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 our bodies work. We also use oxygen to make steel, create chemicals, treat water, and as part of rocket fuel.

Sulfur is used to make important chemicals like sulfuric acid. It is also used to make rubber stronger and is part of mixtures for fireworks and treating soil. Selenium is mainly used to make glass and metals, and it helps in farming and electronics. 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 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.

Tellurium is not known to be needed for animal life, but some tiny organisms use it.

Polonium does not play a role in living things.

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. 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

A scientist named Jons Jacob Berzelius called some chemical salts "amphid salts" a long time ago. These salts came from elements in the 16th group of the periodic table, such as 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.