Chemical Properties of Group 16 Elements: Class 12 Chemistry

Chemical Properties of Group \(16\) Elements: Group \(16\) or \({\rm{VIA}}\) elements are generally called the oxygen family. It includes the elements such as oxygen, sulphur, selenium, tellurium and polonium. Out of these elements, oxygen and sulphur are non-metals, selenium and tellurium are metalloids, and polonium is a radioactive metal. In this article, we are going to discuss the chemical properties of these elements.

Group 16 Elements

 The elements such as oxygen \({\rm{(O)}}\), sulphur \({\rm{(S)}}\), Selenium \({\rm{(Se)}}\), tellurium \({\rm{(Te)}}\) and polonium \({\rm{(Po)}}\) constitute the group \(16\) or \({\rm{VIA}}\) of the periodic table. The first two members of this group are non-metals. The next two are metalloids, and the last member of the family is a radioactive element with a very short life period. Group \(16\) elements are collectively called chalcogens (ore-forming) because many of the metal ores occur as oxides and sulphides.

All the elements in group \(16\) have an \({\rm{n}}{{\rm{s}}^2}{\rm{n}}{{\rm{p}}^4}\) electronic configuration. This means that all of them have six electrons in their outermost shell.

Let us go through the chemical properties of these elements.

Chemical Properties of Group 16 Elements

1. Oxidation States

In group \(16\) elements, the four p-electrons in the outermost shell are arranged in the three ‘\({\rm{p}}\)’ orbitals as \({\rm{np}}_{\rm{x}}^2{\rm{np}}_{\rm{y}}^1{\rm{np}}_{\rm{z}}^{\rm{1}}.\) Hence, there are two half-filled ‘\({\rm{p}}\)’ orbitals that are responsible for the chemical bonding with other elements. Therefore, they show the properties of normal elements with a valency of \(2\) and a maximum valency of \(6\).

For example, \(-2\) is the predominant oxidation state of oxygen. The stability of the \(-2\) oxidation state decreases down the group. Thus, polonium rarely shows a \(-2\) oxidation state. As oxygen is less electronegative than fluorine, in \({\rm{O}}{{\rm{F}}_2}\), it has a \(+2\) oxidation state. The other elements show \( + 2,\, + 4,\, + 6\) oxidation states. Out of these, \(+4\) are \(+6\) more common. The stability of the \(+6\) oxidation state decreases down the group while that of the \(+4\) oxidation state increases due to the inert pair effect.

2. Trends in Chemical Reactivity

The chemical reactivity of the elements varies from the highly electronegative element oxygen to the decidedly metallic polonium. The chemical reactivity of the group \(16\) elements towards the metals and hydrogen decreases while moving down the group. The element oxygen combines with both metals and non-metals generally at a higher temperature. However, the element oxygen is inert at room temperature because the atoms in the oxygen molecule are held together by a strong double covalent bond. Therefore, it is difficult to break these bonds.

3. Reaction with Hydrogen

All the elements of group \(16\) combine with hydrogen and form volatile hydrides (Binary compounds of hydrogen with other elements are called hydrides) of the type \({{\rm{H}}_2}{\rm{R}}\). Water, \({{\rm{H}}_2}{\rm{O}}\) is a liquid, whereas the other hydrides are offensive smelling gases at normal temperature. The liquid nature of \({{\rm{H}}_2}{\rm{O}}\) is due to the presence of hydrogen bonding in the molecules of water.

The stability of the hydrides decreases from oxygen to polonium as we go down the group, the size of the central atom increases. This prevents the formation of a stable covalent bond between the large and small atoms. Thus, a small-sized oxygen atom forms a strong bond with hydrogen, while polonium which is a very large atom, does not form a stable covalent bond. Due to the decrease in stability of the hydrides, the tendency to give hydrogen increases and hence, the reducing character of the hydrides decreases down the group.

The acidic nature of the hydrides increases from \({{\rm{H}}_2}{\rm{O}}\) to \({{\rm{H}}_2}{\rm{Te}}\) because of the decrease in bond enthalpy.

4. Reaction with Oxygen

The group \(16\) elements such as sulphur, selenium and tellurium combine with oxygen to form the oxides of the type \({\rm{M}}{{\rm{O}}_2}\) and \({\rm{M}}{{\rm{O}}_3}\). Out of these, the trioxides are more acidic than the dioxides. Let us discuss them in detail:

(i) Oxides of MO₂ Type

The elements such as sulphur, selenium and tellurium combine with oxygen to form the oxides such as \({\rm{S}}{{\rm{O}}_2},\,{\rm{Se}}{{\rm{O}}_2}\) and \({\rm{Te}}{{\rm{O}}_2}\)_, respectively. The oxidation number of the central atom in these oxides is \(+4\). The \({\rm{S}}{{\rm{O}}_2}\) is a gas, \({\rm{Se}}{{\rm{O}}_2}\) is a volatile solid, and \({\rm{Te}}{{\rm{O}}_2}\) is a non-volatile crystalline solid. These oxides generally dissolve in water to form the corresponding acids of the general formula \({{\rm{H}}_2}{\rm{M}}{{\rm{O}}_3}\). For example, sulphur dioxide dissolves in water to form sulphurous acid. That is,

\({\rm{S}}{{\rm{O}}_2} + {{\rm{H}}_2}{\rm{O}} \to {{\rm{H}}_2}{\rm{S}}{{\rm{O}}_3}\)

Similarly, selenium dioxide dissolves in water to form selenous acid. That is,

\({\rm{Se}}{{\rm{O}}_2} + {{\rm{H}}_2}{\rm{O}} \to {{\rm{H}}_2}{\rm{Se}}{{\rm{O}}_3}\)

The strength of the acids thus formed is,

\({{\rm{H}}_2}{\rm{S}}{{\rm{O}}_3} > {{\rm{H}}_2}{\rm{Se}}{{\rm{O}}_3} > {{\rm{H}}_2}{\rm{Te}}{{\rm{O}}_3}\)

(ii) Oxides of MO₃ Type

The elements such as sulphur, selenium and tellurium also combine with oxygen to form the oxides of \({\rm{M}}{{\rm{O}}_3}\) type. They are \({\rm{S}}{{\rm{O}}_3},\,{\rm{Se}}{{\rm{O}}_3}\) and \({\rm{Te}}{{\rm{O}}_3}\)_, respectively. However, such oxides are difficult to prepare compared to dioxide.

The sulphur trioxide \(\left( {{\rm{S}}{{\rm{O}}_3}} \right)\) is made by the catalytic oxidation of sulphur dioxide \(\left( {{\rm{S}}{{\rm{O}}_2}} \right)\). Selenium trioxide \(\left( {{\rm{Se}}{{\rm{O}}_3}} \right)\) is prepared by passing an electric discharge through the vapours of selenium and oxygen at \({\rm{4mm}}\) pressure. Similarly, tellurium trioxide \(\left( {{\rm{Te}}{{\rm{O}}_3}} \right)\) is produced by the strong heating of telluric acid.

These trioxides are acidic in nature, and they dissolve in water to form the corresponding acids. For example, sulphur trioxide dissolves in water to form sulphuric acid. That is,

\({\rm{S}}{{\rm{O}}_3} + {{\rm{H}}_2}{\rm{O}} \to {{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4}\)

The strength of the acids thus formed decreases with the increase in molecular weight. The decreasing order the acid strength will be,

\({{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4} > {{\rm{H}}_2}{\rm{Se}}{{\rm{O}}_4} > {{\rm{H}}_2}{\rm{Te}}{{\rm{O}}_4}\)

5. Reaction with Halogen

All the elements of group \(16\) combine with halogens to form different types of halides such as monohalides, dihalides, tetrahalides and hexahalides.

The different formula halides formed by group \(16\) elements are given in the table:

Let us explain different types of halides formed by group \(16\) elements in detail:

(i) Monohalides: The important monohalides formed from group \(16\) elements are \({{\rm{S}}_2}{{\rm{F}}_2},\;{{\rm{S}}_2}{\rm{C}}{{\rm{l}}_2},\,{{\rm{S}}_2}{\rm{B}}{{\rm{r}}_2},\,{\rm{S}}{{\rm{e}}_2}{\rm{C}}{{\rm{l}}_2}\) and \({\rm{S}}{{\rm{e}}_2}{\rm{B}}{{\rm{r}}_2}\). They are dimeric halides. These halides undergo disproportionation reaction as,

\(\mathop {2{\rm{S}}{{\rm{e}}_2}{\rm{C}}{{\rm{l}}_2}}\limits^{ + 1} \to \mathop {{\rm{SeC}}{{\rm{l}}_4}}\limits^{ + 4} + \mathop {3{\rm{Se}}}\limits^0 \)

The structure of the above halides is similar to that of \({{\rm{H}}_2}{{\rm{O}}_2}\). For example, the structure of \({{\rm{S}}_2}{\rm{C}}{{\rm{l}}_2}\) is,

(ii) Dihalides: Except oxygen, all elements of group \(16\) forms dichlorides and dibromides. The dihalides are formed by \({\rm{s}}{{\rm{p}}^3}\) hybridisation and have a tetrahedral structure. Because of the presence of two lone pairs of electrons, these dihalides will have a net structure found as in water. For example, the structure of \({\rm{SC}}{{\rm{l}}_2}\) is.

(iii) Tetrahalides: The elements of group \(16\) will form tetrahalides like \({\rm{S}}{{\rm{F}}_4},\,{\rm{Se}}{{\rm{F}}_4},\,{\rm{Te}}{{\rm{F}}_4}\), etc. They have \({\rm{s}}{{\rm{p}}^3}\) hybridisation and generally have a trigonal bipyramidal structure where one of the equatorial positions is occupied by a lone pair of electrons. Such type of geometry is also known as sea-saw geometry.

For example, the geometry of \({\rm{S}}{{\rm{F}}_4}\) can be given as,

Among the tetrahalides, tetrafluorides are the most stable.

(iv) Hexahalides: Amongst hexahalides, hexafluorides are stable halides. All hexafluorides have an octahedral structure. For example, the sulphur in \({\rm{S}}{{\rm{F}}_6}\) is \({\rm{s}}{{\rm{p}}^3}{{\rm{d}}^2}\) hybridised and has an octahedral structure. It can be represented as,

Anomalous Behavior of Oxygen

Oxygen, which is the first member of group \(16\), differs from other members of the family. This is caused due to its small size, high electronegativity and the non-availability of the \({\rm{d}}\)-orbitals. That is, due to the small size and the high electronegativity of oxygen, the \({\rm{O}}\)-atom carries a partial negative charge in water molecules which results in the strong hydrogen bonding which is found in \({{\rm{H}}_2}{\rm{O}}\) but not in \({{\rm{H}}_2}{\rm{S}}\). Because of the strong electronegativity, the compounds of oxygen are more ionic than the compounds of the other elements of the group.

Due to the absence of \({\rm{d}}\)-orbitals, its covalency is limited to four, whereas the other elements can show covalency beyond four.

Summary

We are now familiar with the chemical properties of group \(16\) elements (the oxygen family). They are also known as chalcogens. Group \(16\) consists of the elements such as oxygen, sulphur, selenium, tellurium and polonium. They generally combine with hydrogen to form the corresponding hydrides, combine with oxygen to form a different type of oxides, and they even combine with halogens to form several halides also. The other chemical properties and the properties of such compounds formed from group \(16\) are explained well in this article.

FAQs on Chemical Properties of Group 16 Elements

Frequently asked questions related to chemical properties of group 16 elements is listed as follows:

Q.1. What are the chemical properties of group \(16\) elements?
Ans: The chemical properties of group \(16\) elements include the trends in chemical reactivity, oxidation state, reaction with oxygen, halogens, hydrogen, etc.

Q.2. What are the chemical properties of an element?
Ans: The chemical properties of an element include acidity, reactivity, flammability, toxicity, the heat of combustion, etc.

Q.3. Is conductivity a chemical property?
Ans: No, conductivity is not a chemical property. It is a physical property.

Q.4. What are group 16 elements called?
Ans: Group \(16\) elements are generally called chalcogens.

Q.5. Why is group 16 called chalcogens?
Ans: Group \(16\) elements are generally called chalcogens (ore-forming) because many of the metal ores occur as oxides and sulphides.

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