Chalcogens are the Group 16 elements of the modern periodic table consisting of 5 elements oxygen, sulphur, selenium, tellurium and polonium. The elements in this group are also known as chalcogens or ore-forming elements because many elements can be extracted from sulphide or oxide ores. The chalcogens are the elements that belong to group 16 of the modern periodic table (or the oxygen family).
In this article, we are going to learn about what are chalcogens, elements under the chalcogen family and their properties in detail.
What are Chalcogens?
Group 16 elements also called Chalcogens are the elements in the oxygen family. They are a group of five elements: oxygen, sulfur, selenium, tellurium, and polonium. Sometimes oxygen is excluded from the chalcogen family for generalizing the chemical properties of the group. The chemical properties of oxygen are quite different from the other members of the group.
The synthetic element Livermorium (symbol Lv) is also considered a part of the chalcogen family.
How to Isolate Chalcogens?
To isolate elements of chalogens various methods are used that include,
- Oxygen is one of the largest constituent of air and separation of air results in the formation of oxygen and nitrogen.
- We can easily extract Sulfur from natuarla oil and petroleum.
- Tellurium and Selenium are produced as the byproduct of refining of copper.
- Particle accelerators is used to create Livermorium and Polonium.
Elements of Chalcogen Family
In the modern periodic table, Chalcogens is composed of five elements: oxygen, sulphur, selenium, tellurium, and polonium. Oxygen is abundant on the planet. When the proportions of different types of atoms found in the universe were calculated, oxygen was determined to be the fourth most abundant element after hydrogen, helium, and neon. It constitutes about 89% of water, 46% of the earth's crust and 20 % of the air.
Electronic Configuration of Chalcogen Family
The symbol, atomic number and electronic configuration of elements of Chalcogens are given below in this article.
|
Oxygen | O | 8 | [He] 2s2 2p4 |
Sulphur | S | 16 | [Ne] 3s2 3p4 |
Selenium | Se | 34 | [Ar] 3d10 4s2 4p4 |
Tellurium | Te | 52 | [Kr] 4d10 5s2 5p4 |
Polonium | Po | 84 | [Xe]4f14 5d10 6s2 6p4 |
Now let's learn about them in detail.
Oxygen
Oxygen is denoted by the symbol O. It is a colourless and odourless gas that is converted into carbon dioxide during the human respiration process. Oxygen is a diatomic molecule. Oxygen is also found in trace amounts as a triatomic molecule (O3), which is known as ozone. Many elements combine easily with oxygen. The evolution of heat energy occurs during the combination of some elements; this process is known as combustion.
Sulphur
Symbol S represents sulfur. It's a nonmetal that ranks ninth in terms of cosmic abundance. Sulphur can be found in both the combined and free states. Sulfates account for about 0.09 per cent of the sulphur found in seawater. The meteorite contains 12% sulphur, and a significant amount of sulphur is found in underground deposits of pure sulphur present in dome-like structures. Sulphur is formed in this environment by the action of anaerobic bacteria on sulphate minerals such as gypsum.
Selenium
Selenium is rarer than oxygen or sulphur. It can be found in a few minerals both free and combined with heavy metals (such as lead, silver, or mercury). Under typical settings, the grey metallic form of selenium is the most stable form of the element.
Tellurium
Tellurium is a chemical element with the atomic number 52 and properties intermediate between metals and nonmetals. It is one of the earth's crust's rarest stable elements. It is frequently found in its free state as well as in compounds with elements such as copper, lead, silver, and gold.
Polonium
It is the rarest element in the group of sixteen elements. It is a radioactive substance. Polonium is occasionally used in alpha radiation applications in science.
Physical Properties of Group 16 Elements (Chalcogens Family)
Some important physical properties of Group 16 elements are:
- Electronic Configuration
- Atomic/Ionic Radii
- Ionization Enthalpies
- Electron Gain Enthalpies
- Electronegativities
- Metallic Nature
- Melting and Boiling Points
Now, we will study them in detail.
Electronic Configuration
Group 16 elements or elements of the oxygen family have six electrons in their outermost shell. So the general electronic configuration of them is ns2, np4. Electronic configuration of each member of the oxygen family is,
|
Oxygen(O) | [He] 2s2 2p4 |
Sluphur(S) | [Ne] 3s2 3p4 |
Selenium(Se) | [Ar] 3d10 4s2 4p4 |
Tellurium(Te) | [Kr] 4d10 5s2 5p4 |
Polonium(Po) | [Xe]4f14 5d10 6s2 6p4 |
Atomic/Ionic Radii
Atomic radii or ionic radii of elements increase as they move down the periodic table. The chalcogen with the smallest atomic and ionic radius (excluding livermorium) is oxygen, and the chalcogen with the largest (excluding livermorium) is polonium. The addition of protons and the increase in effective nuclear charge cause elements' atomic radii to decrease over time. As a result, the atomic radius of oxygen will be much smaller than that of lithium.
Ionization Enthalpies
Ionization Enthalpies of the elements of the oxygen family are less compared to those of the nitrogen family. The general trend of moving down the group from oxygen to polonium, suggests that the ionization enthalpy or potential decreases on moving down the group.
On moving left to right the general trend of the ionization enthalpy suggest that it increases along the period.
Electron Gain Enthalpies
Electron Gain Enthalpies decrease with an increase in the atom's size. As a result, the electron gain enthalpies of the chalcogens decrease as one moves down the group. It is worth noting that oxygen has a lower negative electron gain enthalpy than sulphur, which can be attributed to the compressed atomic structure of oxygen, which contributes to interelectronic repulsion between the valence electrons and any other approaching electron.
Electronegativities
Electronegativity decreases as one moves down a group due to a variety of factors, including an increase in atomic radius and an increase in electron-electron repulsion. The most electronegative chalcogen is oxygen, and the least electronegative chalcogen is polonium (livermorium not considered).
Metallic Nature
Non-metal elements include oxygen and sulphur. Metalloids include selenium and tellurium. Under normal conditions, polonium has metallic properties. It should be noted, however, that polonium is a radioactive element.
Melting and Boiling Points
Melting and Boiling points of elements increase as they progress down a group due to the increase in atomic sizes and atomic masses (as a result of increased intermolecular forces of attraction). Among chalcogens, oxygen has the lowest melting and boiling points. The significant difference in the melting and boiling points of sulphur and oxygen can be attributed to the fact that oxygen exists in the atmosphere as a diatomic molecule, whereas sulphur is typically found as a polyatomic molecule.
Note:
- Fluorine is the most electronegative element while Oxygen is the second most electronegative element.
- All the members of group 16 i.e. oxygen family exhibit allotropy.
- Sulphur(S) in the oxygen family show catenation property similar to that of carbon.
Chemical Properties of Group 16 Elements
Some important chemical properties of Group 16 elements are:
- Allotropes
- Oxidation States
- Reactions with Hydrogen
Now, we will study them in detail.
Allotropes
Almost all chalcogens have multiple allotropes. The most common oxygen allotropes are dioxygen and ozone. In fact, there are nine known allotropes of oxygen. Furthermore, there are over 20 known allotropes of sulphur. Selenium is known to have at least five different allotropes, while polonium is known to have two. Monoclinic sulphur and rhombic sulphur are the two most stable allotropic forms of sulphur. It should be noted that selenium and tellurium are both crystalline and amorphous elements.
Oxidation States
Because the chalcogens' general electronic configuration is ns2 np4, they can achieve a stable electronic configuration by gaining two electrons or participating in covalent bonding. When they gain two electrons, the ion formed has the general formula M2- (where M denotes a chalcogen). The chalcogens exhibit regular oxidation states of -2, +2, +4, and +6.
Reactions with Hydrogen
When chalcogens react with dihydrogen, they usually form hydrides with the general formula H2M (where M can be any chalcogen – oxygen, sulphur, selenium, tellurium, or polonium). This chemical reaction takes the following general form:
M (chalcogen) + H2 (dihydrogen) → H2M (hydride of the chalcogen)
Chemistry of Livermorium
Livermorium with atomic number Z=116 is the newest member of the Oxygen family. In the May of 2012, IUPAC approved the name "Livermorium" (symbol Lv) for the element with atomic number 116 which becomes the newest member of the Group 16 elements. It is a heavy element and is radioactive in nature.
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