What are Chalcogens Definition Electronic Configuration Properties and Common Compounds
What are Chalcogens?
Chalcogens are the elements belonging to the group 16 according to the modern periodic table. There are five different chalcogen elements, which are, oxygen, sulfur, selenium, tellurium, and polonium. Livermorium, denoted by Lv, is a synthetic element which is believed to belong to the chalcogen group. However, it is not an uncommon situation wherein oxygen is excluded when it comes to the chalcogen family. The oxygen family characteristics are quite different from the other elements of the groups.
All the elements of the chalcogen family have 6 valence shell electrons. They are also referred to as ore-forming elements because a huge of metals exist in the oxides or sulphides form in the Earth’s crust. Many chalcogens from the chalcogen group also tend to occur as different allotropes, for example, oxygen consists of 9 allotropes and on the other hand, sulphur has more than 20. However, tellurium has just one allotrope known so far. In this article, we will learn about what are chalcogens, and their physical and chemical properties.
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Electron Affinity Order of Chalcogens
The general electronic configuration of the chalcogens elements is written as ns²np⁴, wherein, ‘n’ refers to the value of the principal quantum number which corresponds to the valence shell of an element. The electronic configurations of chalcogens are shown below.
The electron configuration of livermorium, which is believed to be a chalcogen element, is predicted as [Rn]5f¹⁴6d¹⁰7s².
Physical Properties of Chalcogens
Atomic/Ionic Radii of the Chalcogens
The atomic radii also called as the ionic radii of elements tend to increase when it progresses down a group. The chalcogen having the lowest atomic radius is oxygen, whereas the chalcogen having the largest atomic radius is polonium (excluding livermorium).
The atomic radii of elements tend to decrease across periods because of the addition of protons and the increasing effective nuclear charge. Hence, the atomic radius of oxygen is much smaller when compared to lithium.
Ionization Enthalpies of Chalcogens
The ionisation enthalpy decreases as the radius or the size of the atom increases. Hence, the ionisation enthalpies of the chalcogens tend to decrease when progressing down in the group. Amongst all the chalcogen elements, oxygen is known to have the highest ionization enthalpy.
The ionisation enthalpy tends to increase when progressing across the group since there is an increase in the effective nuclear charge as we progress across the period. Hence, oxygen has a higher ionisation enthalpy than lithium.
Electron Gain Enthalpies of Group 16 Elements
As the size of the atom tends to increase, the electron gain enthalpy tends to decrease. Hence, the electron gain enthalpies of chalcogens tend to decrease while progressing down the group. However, oxygen has a lesser negative electron gain enthalpy than sulfur, which is explained by the compressed atomic structure that oxygen has, which tends to contribute to the interelectronic repulsion that occurs between the valence electrons and other approaching electrons.
Electronegativities of Chalcogens
The electronegativity tends to decrease when progressing down the group because of several factors like the increase in the electron-electron repulsion and the increase in the atomic radius. The most electronegative known chalcogen element is oxygen and the least electronegative known chalcogen element is polonium when we do not consider livermorium.
Metallic Nature of the Group 16 Elements
Oxygen and sulfur are non-metals.
Selenium and tellurium are metalloids.
Under the standard conditions, polonium tends to exhibit metallic characteristics. However, polonium is a radioactive element.
Chemical Properties of the Chalcogens
Allotropy Exhibited by Group 16 Elements
Almost all of the chalcogens have more than one allotrope. The most common allotropes of oxygen are known as dioxygen and ozone. Oxygen has 9 different allotropes that are known. Furthermore, sulfur has more than 20 known allotropes.
Selenium has at least 5 different allotropes and polonium has 2 allotropes. The two most stable allotropes of sulfur are known as monoclinic sulfur and rhombic sulfur. Selenium and tellurium tend to exist in both the crystalline and amorphous forms.
Reactions Between Group 16 Elements and Hydrogen
Chalcogens tend to form hydrides when they react with dihydrogen and has a generic formula H₂M, wherein, M refers to any given chalcogen element. The generic format of the chemical reaction is as follows:
M (chalcogen) + H₂ (dihydrogen) → H₂M (hydride of chalcogen)
FAQs on Chalcogens in Group 16 of the Periodic Table
1. What are chalcogens in chemistry?
The chalcogens are the Group 16 elements of the periodic table: oxygen, sulfur, selenium, tellurium, and polonium.
- They are also called the oxygen family.
- They have six valence electrons with general outer configuration ns2 np4.
- They commonly form −2 oxidation state compounds, such as O2 in water (H2O) and sulfide ion S2-.
- The name “chalcogen” means “ore-forming,” because many metal ores are oxides or sulfides.
2. Which elements belong to Group 16 (the oxygen family)?
The elements in Group 16 are oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po).
- Atomic numbers: O (8), S (16), Se (34), Te (52), Po (84).
- Oxygen and sulfur are nonmetals; selenium and tellurium are metalloids; polonium is metallic and radioactive.
- All show similar valence shell configuration ns2 np4, giving related chemical properties.
3. What is the general electronic configuration of chalcogens?
The general electronic configuration of chalcogens is ns2 np4 in the outermost shell.
- They have six valence electrons.
- They need two more electrons to complete an octet, so they commonly form 2− ions (e.g., O2-, S2-).
- This configuration explains their typical oxidation states of −2, +4, and +6.
4. What are the common oxidation states of chalcogens?
The most common oxidation states of chalcogens are −2, +4, and +6.
- −2 state: seen in H2O and H2S.
- +4 state: seen in SO2 and SeO2.
- +6 state: seen in SO3 and H2SO4.
- Oxygen usually shows −2 but can show −1 in peroxides like H2O2.
5. How does the reactivity of chalcogens change down the group?
The reactivity of chalcogens generally decreases down Group 16.
- Oxygen is highly reactive and forms strong oxides.
- Reactivity decreases from sulfur to tellurium due to increasing atomic size and decreasing electronegativity.
- Oxidizing power decreases down the group.
- Metallic character increases from oxygen to polonium.
6. Why is oxygen different from other chalcogens?
Oxygen differs from other chalcogens due to its small size, high electronegativity, and absence of d-orbitals.
- It forms strong hydrogen bonds in H2O.
- It cannot expand its octet, unlike sulfur or selenium.
- It commonly forms O=O double bonds in O2.
- It shows unique oxidation states like −1 in peroxides (H2O2).
7. What are hydrides of chalcogens?
Hydrides of chalcogens are binary compounds formed between hydrogen and Group 16 elements, such as H2O, H2S, H2Se, and H2Te.
- They have the general formula H2E (E = chalcogen).
- Acidity increases down the group: H2O < H2S < H2Se < H2Te.
- Thermal stability decreases down the group.
8. How are sulfur dioxide and sulfur trioxide formed?
Sulfur dioxide is formed by burning sulfur in oxygen, and sulfur trioxide is formed by further oxidation of sulfur dioxide.
- Formation of sulfur dioxide: S(s) + O2(g) → SO2(g)
- Formation of sulfur trioxide: 2SO2(g) + O2(g) → 2SO3(g) (in presence of catalyst V2O5).
- These reactions are key steps in the Contact Process for manufacturing sulfuric acid.
9. What are the physical properties of chalcogens?
Chalcogens show a gradual change from nonmetallic to metallic properties down the group.
- Oxygen is a diatomic gas (O2).
- Sulfur is a yellow solid, commonly as S8 rings.
- Density, melting point, and boiling point increase down the group.
- Electrical conductivity increases from sulfur (poor conductor) to tellurium (semiconductor).
10. What is the importance of chalcogens in everyday life and industry?
Chalcogens are essential elements widely used in biological systems, industry, and chemical manufacturing.
- Oxygen is vital for respiration and combustion.
- Sulfur is used to produce H2SO4, one of the most important industrial chemicals.
- Selenium and tellurium are used in semiconductors and photovoltaic cells.
- Many metal ores occur as oxides or sulfides, such as Fe2O3 and ZnS.
