Notes on group 16 elements

The oxygen family, commonly known as chalcogens, comprises group 16 elements of the periodic table and is regarded as one of the significant group elements. It is composed of oxygen, sulphur, selenium, tellurium, and polonium. Nature has them in both free and mixed states.

The components in group 16 are strongly tied to life. We require oxygen all our lives. It is in charge of specific protein structures in all living species. Because several elements in this group may be recovered from sulphide or oxide ores, they are frequently referred to as chalcogens or ore-forming elements.

Electronic configuration of group 16 elements

• The electronic configuration of the valence shell of the group 16 elements is of the kind ns2np4. As a result, they contain six electrons in their valence shell, with two in the s subshell and four in the p subshell, respectively.

The first four elements in the group 16 elements are collectively called chalcogens, which means “ore-forming elements.” This is because many metal ores may be found in the earth’s crust in the form of sulphides or oxides. Natural oxygen is the most abundant element found in large quantities in the environment. It shapes 20.946 percent of the world’s air volume and 46.6 percent of the world’s mass in many forms, including silicates and diverse compounds such as carbonates, oxides, and sulphates.

• Oxygen: O represents the chemical symbol for oxygen. It is a colourless and odourless gas utilized in human respiration and transformed into carbon dioxide. The oxygen molecule is diatomic (O2). Ozone is a triatomic molecule (O3) present in remnants of oxygen. Oxygen readily mixes with numerous elements. Combustion occurs when specific components are combined, releasing heat energy.

• Sulphur: Sulphur is represented by the letter S. It is a non-metal eighth in cosmic abundance.Sulphur is present in both the combined and free states. Seawater contains around 0.09 percent sulphur in the form of sulphates. The meteorite includes 13% sulphur, which comes from subsurface deposits of pure sulphur in dome-like formations. Anaerobic bacteria operate on sulphate minerals like gypsum to produce sulphur.

• Selenium: Selenium is rarer than oxygen and sulphur. It is free and associated with heavy metals (such as lead, silver, or mercury). Under typical conditions, selenium’s metallic grey form is the most stable.

• Tellurium: Tellurium (atomic number 52) is a chemical element that has characteristics of both metals and non-metals. In the earth’s crust, it is the rarest stable element. It is found in free form and combinations with copper, lead, silver, and gold.

• Polonium: Polonium is the rarest element in Group 16. It is radioactive. It is sometimes utilized in alpha radiation research.

Physical properties of group 16 elements

The atomic and ionic radius rises when we proceed from oxygen to polonium. Group 16 elements physical properties are discussed below:

Ionization enthalpy

When the size of the central atom is increased, the ionization enthalpy drops. As a result, it reduces as we progress from oxygen to polonium because the size of the atom grows in size as we progress down the periodic table.

Electron gain enthalpy

As the size of the central atom increases, the electron gain enthalpy drops as the central atom moves down the group. The negative electron gain enthalpy of the oxygen molecule is smaller than that of the sulphur molecule. Due to the compressed structure of oxygen, there is more repulsion between the electrons already present and the oncoming electron.

Electronegativity

As we progress through the group, the electronegativity diminishes. As a result, it diminishes as we progress from oxygen to polonium, owing to the rise in the size of the nucleus. Learn everything there is to know about electronegativity right now.

Nature of group 16 elements

Oxygen and sulphur are non-metals, while Selenium and Tellurium are metalloids, and polonium is metal under normal circumstances. Polonium is a radioactive element that can cause cancer.

Allotropy

Allotropy is present in every element of group 16. Oxygen exists in two forms: oxygen(O2) and ozone (O3).

The element sulphur exists in various allotropic forms, but only two are stable, and they are Rhombic Sulphur and Monoclinic Sulphur, respectively. It is possible to find amorphous and crystalline forms of Selenium and Tellurium.

Melting and boiling points

As atomic size grows from oxygen to tellurium, the melting and boiling points of the elements increase as well. According to the concept that oxygen exists as a diatomic atom and sulphur exist as a polyatomic particle, the vast difference in the melting and boiling temperatures of oxygen and sulphur may be explained.

Oxidation states

Because the group 16 elements have an ns2 np4 in their outer shell, they can achieve noble gas configuration either by gaining two electrons, forming M-2, or by sharing two electrons, forming two covalent bonds.

Hydrogen bonds

Because of their small size and strong electro-negativity, oxygen can form solid hydrogen bonds with other elements. It is worth noting that the alternate elements in this group have poor electro-negativities and do not form hydrogen bonds.

Chemical properties of group 16 elements

Reaction with oxygen

Molecules of the type MO2 and MO3 are formed when elements of the 16th group interact with oxygen. Trioxides are less acidic than dioxides.

MO2 oxides

Sulphur, selenium, and tellurium react with oxygen to generate oxides: SO2, SeO2, and TeO2. The center atom in these oxides is oxidized to +4. SO2 is a gas, SeO2 is a liquid, and TeO2 is a crystalline solid. These oxides dissolve in water to generate H2MO3 acids. In water, sulphur dioxide dissolves to generate sulphuric acid. So,

SO2+H2O→H2SO3

The same goes for selenium dioxide and water. So,

SeO2+H2O→H2SeO3

The resulting acids strength is,

H2SO3 > H2SeO3 > H2TeO3

MO3 oxides

Sulphur, selenium, and tellurium react with oxygen to generate MO3 oxides. They are SO3, SeO3, and TeO3. Unlike dioxide, these oxides are difficult to manufacture.

In the catalytic oxidation of sulphur dioxide (SO2), sulphur trioxide (SO3 ) is produced . An electric discharge through selenium and oxygen vapours at 4mm pressure produces selenium trioxide (SeO3). Similarly, severe heating of telluric acid yields tellurium trioxide (TeO3).

These trioxides are acidic and dissolve in water to create acids. The sulphur trioxide in water forms sulphuric acid. So,

SO3 + H2O → H2SO4

The strength of the resulting acids diminishes with molecular weight. The weaker the acid,

H2SO4 > H2SeO4 > H2TeO4

Reaction with hydrogen

To generate volatile hydrides of type H2R, all elements in group 16 interact with hydrogen to form hydrides. Other hydrides are odorous gases at room temperature, whereas water is a liquid. Hydrogen bonding in water molecules gives it a liquid state.

From oxygen to polonium, the stability of the hydrides diminishes as the central atom grows in size. The big and small atoms cannot form a stable covalent connection. So a tiny oxygen atom creates a strong covalent connection with hydrogen, whereas substantial atom-like polonium does not. It is important to note that the hydride’s lowering character reduces as its stability decreases. With decreasing bond enthalpy, hydrides become acidic.

Reaction with halogen

They all mix with halogens to generate halides (mono-, di-, tetrahalides, and hexahalides).

Conclusion

We now know the chemistry of group 16 elements. (the oxygen family). Group 16 elements include oxygen, sulphur, selenium, tellurium, and polonium elements. They produce hydrides with oxygen, various oxides, and halogens with hydrogen.