Group 16: Chalcogen Family

Group 16 is also called oxygen family. This group includes Oxygen (O), Sulfur (S), Selenium (Se), Tellurium (T) and Polonium (Po) and Livermorium (Lv). This group is also known as Chalcogen Family. Group 16 elements are non-metals with high ionization energy. They are found in free and combined state, and are sometimes referred to as ore-forming elements. Group 16 elements have six valence electrons. They have a tendency to gain two electrons, while losing two electrons. Group 16 elements can be extracted from oxide ores. Oxygen is a colorless gas with high electronegativity. It is essential for all life forms. Oxygen has a limited tendency for catenation, where it forms bonds with identical atoms. From all the elements in the universe, sulfur is the most abundant on Earth. Sulfur, like phosphorus, is an inorganic element. The most common basic triode is sulfur trioxide. The element Tellurium is not metallic, but it is present in the earth’s crust. Tellurium is found in a variety of selenides, and is also present as a metal (Peterson & Stoll, 2003).

 

1. Electronic configuration of Group 16 elements

General electronic configuration of group 16 is ns2 np4 while the electronic configuration of group 16 members is as follows (Knapp, 2004).

 

O [8] 1s2 2s2 2p4 or [He] 2s2 2p4
S [16] 1s2 2s2 2p6 3s2 3p4 or [Ne] 3s2 3p4
Se [34] 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4 or [Ar] 3d10 4s2 4p4
Te [52] 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p4 or [Kr] 5s2 4d10 5p4
Po [84] 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p4 or [Xe] 6s2 4f14 5d10 6p4
Lv [116] 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10 7p4 or [Rn] 7s2 5f14 6d10 7p4

 

2. Anomalous behavior of Oxygen

* Unlike most chemical elements, oxygen has an unusual behavior. It exhibits anomalous properties at different temperatures. This makes it one of the most abundant elements in the universe.
* The anomalous behavior of oxygen is caused by two different factors. First, oxygen is a member of the chalcogen group. This means that it does not have d-orbitals in its valence shell. Secondly, the single bond that it has is weaker than that of other chalcogens. This means that oxygen cannot exhibit oxidation states beyond 2.
* The other factor causing the anomalous behavior of oxygen is the p-p bond that it forms with other elements. Oxygen molecules are able to form p-p bonds because of its high electronegativity. However, the p-p bond is weaker than sigma bonds. This makes it possible for oxygen to form compounds with other elements.

 

3. Trend in the physical properties of Group 16 Elements

Group 16 elements are characterized by a low first ionization enthalpy. They also have higher second ionization enthalpy. They also have an increased number of inner electrons. They are also less susceptible to dry air at room temperature. They have an increased van der Waals force. They are primarily solids at ordinary temperatures. Group 16 elements show following trend in their physical properties (Woollins, et al., 2011).

 

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3.1. Atomic and ionic radii of Group 16 Elements

Atomic and ionic radius of group 16 elements increases from oxygen to polonium while atomic and ionic radii of Livermorium is unknown.

 

Atomic radius group 13 periodic table

 

Figure 1: Atomic radius of Group 16 elements

 

Ionic radius group 13 periodic table

 

Figure 2: Ionic radius of Group 16 elements

 

3.2. Ionization energy of Group 16 Elements

Ionization energy of group 16 elements decrease from oxygen to Livermorium
Ionization energy of group 16 elements in kilo joule per mole:

 

First ionization energy group 13 periodic table

 

Figure 3: First Ionization Energy of the Group 16 elements

 

3.3. Electronegativity of Group 16 Elements

Electronegativity of group 16 elements decrease from oxygen to polonium while this value is unknown for Livermorium

 

O     3.5

S    2.5

Se   2.4

Te    2.1

Po    2.0

 

3.4. Melting and boiling point of Group 16 Elements

Melting and boiling point of group 16 elements increase from oxygen to Livermorium while melting and boiling point of tellurium is highest among all the group members.

 

melting and boiling points group 13 periodic table

 

Figure 4: Melting and Boiling Points of the Group 16 elements

 

4. Chemical properties of Group 16 Elements

Group 16 elements form hydrides with hydrogen, and are capable of forming halides with halogens. These elements can also form oxides. . The elements of group 16 have a greater number of electrons than group 15 elements (Knapp, 2004; Woollins, et al., 2011).

 

4.1. Allotropy of group 16 elements

 

4.1.1. Allotropes of oxygen

Oxygen has two allotropes – ozone and dioxygen. Ozone, an oxygen allotrope, has a strong stench and is toxic to living things. Ozone is formed by electric discharge in the presence of molecular oxygen. Its chemical properties are very similar to dioxygen. Ozone is an important oxidizing agent in the atmosphere. Its chemical properties are important for the immune system, as it functions as a shield against UV radiation. It has more oxidative ability than dioxygen.

 

4.1.2. Allotropes of Sulfur

• Unlike other chemical elements, sulfur has a large number of allotropes. Allotropes are structural modifications that allow the atoms of a certain element to be changed over to another without changing their mass.There are 30 allotropes of sulfur. These allotropes have different bond lengths, angles, and compositions.
• Among the chemical elements, sulphur is second only to carbon in the number of solid allotropes it forms. Sulphur allotropes contain cyclic sulphur molecules with S8 puckered rings. Each ring consists of 8 sulphur atoms, and the inter-bond angle ranges from 45 degrees to 90 degrees. These ring structures decrease the intra-chain and inter-chain distances.

 

4.1.3. Allotropes of selenium

• Having properties similar to sulphur, selenium is found in many allotropes. These include metallic, amorphous, and crystalline forms. Selenium is a trace element that is essential for animals and plants. The most widely used form is black selenium. In addition to its role in xerography, sound films, and alarm devices, selenium is also used in photocells and solar panels.
• It is found in seafood and poultry. It also increases antioxidant levels in the body. Currently, it is used as a ceramic pigment. It has also been used to increase the abrasion resistance of vulcanized rubber. It is also used as an ingredient in anti-dandruff shampoos.

 

4.2. Reaction with halogens

Oxygen reacts with fluorine and form oxygen difluoride and di oxygen difluoride

 

Reaction of Group 13 elements with halogens

Scheme 3: Reaction of Group 16 elements with halogens

 

Conclusion

Often referred to as the oxygen group, group 16 of the periodic table is a family of five chemical elements. These elements are known as Chalcogens. This group is characterized by the presence of electron configurations that involve six electrons in the outermost shell of the atom.

 

References

1. Kilian, P., Knight, F. R., & Woollins, J. D. (2011). Synthesis of ligands based on naphthalene peri-substituted by Group 15 and 16 elements and their coordination chemistry. Coordination Chemistry Reviews, 255(11-12), 1387-1413.
2. Knapp, C., & Passmore, J. (2004). On the way to “solid nitrogen” at normal temperature and pressure? Binary azides of heavier group 15 and 16 elements. Angewandte Chemie International Edition, 43(37), 4834-4836.
3. Peterson, K. A., Figgen, D., Goll, E., Stoll, H., & Dolg, M. (2003). Systematically convergent basis sets with relativistic pseudopotentials. II. Small-core pseudopotentials and correlation consistent basis sets for the post-d group 16–18 elements. The Journal of chemical physics, 119(21), 11113-11123.