The term chalcogens has been derived from the Greek word ‘chalcos’, which literally means ‘ore formers’, as these elements of group 16 in the periodic table are commonly found in copper ores. In this ScienceStruck article, we shall learn about their characteristics and properties in more detail.
|Did You Know?
Humans have been aware of sulfur, a commonly known chalcogen, since ancient times. This element has been mentioned 15 times in the Bible. It was mined by the ancient Romans and Greeks to create incendiary weapons like Greek fire.
Chalcogens are the name of the elements in the periodic table – group 16. The elements in this group are sometimes collectively referred to as the ‘oxygen family’. These elements include oxygen (O), sulfur (S), selenium (Se), polonium (Po), and tellurium(Te). The man-made element livermorium is thought to be a chalcogen too. The compounds of these elements are known as chalcogenides. Of all the elements in this group, only oxygen is a gas, while the rest are solids, and only oxygen and sulfur are usually found in their pure form.
Common Properties of Chalcogens Group
- All chalcogens are very reactive to alkali earth metals.
- All chalcogens found in metallic ores are found in the form of ions.
- Lighter chalcogens such as sulfur and oxygen are non-toxic, and essential to all types of life. On the other hand, heavier chalcogens like tellurium, selenium, and polonium are toxic and quite harmful.
- Chalcogens have various atomic sizes. However, each of these elements have 6 valence electrons. The density, melting and boiling points, and atomic radius increases with bigger atomic weights.
- Oxygen, sulfur, and selenium are non-metals, while tellurium and polonium are semi-metals, and can conduct electricity.
- Usually, the oxidation number of these elements in a chalcogenide is -2. However, in ores such as pyrite, oxidation values can change.
|Elements||Atomic Number||Number of Electrons|
|Sulfur||16||2, 8, 6|
|Selenium||34||2, 8, 18, 6|
|Tellurium||52||2, 8, 18, 18, 6|
|Polonium||84||2, 8, 18, 32, 18, 6|
|Elements||Melting Point in Celsius||Boiling Point in Celsius|
Physical and Chemical Properties of Chalcogens
- The chemical configuration of oxygen is 1s22s22p4.
- Oxygen is known to react with other atoms, and works to form rust through oxidization.
- The smallest chalcogen is oxygen, which has small atoms having 2 and 6 electrons in its shells.
- It is also the least dense at 0.00143 g/cm3.
- Oxygen reaches its boiling point at -297.31°F.
- Oxygen stays in a gaseous, colorless, odorless, and tasteless state at room temperature.
- It makes up 21% of the atmosphere, 46% of the Earth’s crust, and 65% of an average human body.
- Oxygen comes in 2 allotropes – O2 and O3.
- Due to its small size, oxygen is seldom the central atom of the compound, it cannot bond with more than 4 elements.
- Polonium atoms are the largest of all chalcogens, and are comparatively huge, with 2, 8, 18, 32, 18, and 6 electrons in the shells. It has an electron configuration of 1s22s2p63s2p6d104s2p6d10f145s2p6d106s2p4.
- Polonium has the highest density of 9.196 g/cm3.
- Although the boiling point of a chalcogen increases with the atomic weight, polonium is an exception to this trend, as its boiling point is lower than that of tellurium at 1764°F, despite having a bigger atomic weight.
- Polonium is highly radioactive, and it grows with a blue radiance.
- It only occurs in very rare, trace amounts in the Earth’s crust, and is formed by the radioactive decay of uranium and thorium.
- 33 isotopes of this element can be found and created, each of which are radioactive.
- The electron configuration for tellurium is 1s22s2p63s2p6d104s2p6d105s2p4.
- Its boiling point is the highest among the chalcogens at 1810°F.
- Naturally found as a silver metalloid when in its crystalline form, tellurium becomes very weak and brittle.
- It is a photo conductive element.
- Selenium’s electron configuration is 1s22s2p63s2p6d104s2p4.
- Selenium can conduct electricity despite being a non-metal, with a similar charge to tellurium or polonium.
- It is found in its natural state as a reddish powder. However, after processing, it turns black.
- Seawater constitutes around 200 parts per trillion of selenium.
- Selenium is also photo-conductive, which allows it to get electrically charged by exposure to light.
- The electron configuration of sulfur is 1s22s2p63s2p4.
- Sulfur is a yellow solid, and smells horrible – like rotten eggs when burned.
- It is found in trace amounts in the Earth’s crust and in the human body.
- This element is found in a large variety, such as S, S2, S4, S6, and S8.
- Sulfur shows a large range of oxidation states, from -2 to +6, and is widely found in its common oxides SO2 and SO3.
At present, a lot of research is going into supra-molar chemistry with chalcogens. With the success of this work, we can go much further into fields of biology and nano-technology.