Tetravalency of Carbon: Catenation, Hybridisation and Examples

Ever wondered what material is the pencil lead made of? It’s Carbon- the most versatile element and the only element known to form the longest chain of compounds. The Tetravalency of Carbon atom can be defined as the ability of Carbon to bond with other atoms by sharing its valence electrons. 

The atomic number of Carbon is 6, which says that it has 4 electrons in its outermost shell. Carbon follows the octet rule and makes four covalent bonds with other atoms to achieve a stable electrical state. This proves that Carbon is tetravalent. In this article, let us learn more about the Tetravalency of Carbon atom with examples. 

Structure of Carbon

Carbon is the \({15^{th}}\) most abundant element in the Earth’s crust and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. It is the second most abundant element in the human body by mass (about \(18.5\,\% \)) after oxygen.

Symbol: \({\rm{C}}\)

Atomic mass:  \(12.0107\,{\rm{u}}\)

Atomic number: \({\rm{6}}\)

Electron configuration: \([{\rm{He}}]2{{\rm{s}}^2}2{{\rm{p}}^2}\)

Electronegativity: \(2.55\)

Electrons per shell: \(2.\,4\)

Versatile Nature of Carbon

Carbon is present in group \(14\) of the Periodic Table and has \(4\) electrons in its outermost shell. Due to its unique position in the periodic table, Carbon has become the most important of all other elements. Carbon is a versatile element because of the following properties-

1. Atomic size
2. Tetravalency of Carbon
3. Catenating property of Carbon to form long chains with itself

Learn Uses of Carbon

The ground state electronic configuration of Carbon is \(1{{\rm{s}}^2}2{{\rm{s}}^2}2{{\rm{p}}^2}\)

The number of electrons present in the outermost shell is \(4\).

So with \(4\) valence shell electrons, the Carbon atom is expected to either lose, gain or share \(4\) electrons to attain the stable noble gas configuration of Neon \((2,8).\) But  Carbon atoms cannot lose or gain \(4\) electrons. This is because-

1. It would require a large amount of energy to remove four electrons and forming a \({{\rm{C}}^{{\rm{4 + }}}}\) cation with six protons in its nucleus, holding on to just two electrons.
2. It would be difficult for the nucleus with six protons to hold onto \(10\) electrons that is, four extra electrons forming an anion \({{\rm{C}}^{{\rm{4 – }}}}\)

Hence, Carbon undergoes mutual sharing of \(4\) electrons from other atoms resulting in the formation of \(4\) Covalent bonds. And the property of the carbon atom to form \(4\) covalent bonds with other atoms is known as the tetravalency of the Carbon atom. ‘Tetra’ stands for \(4\).

Hybridization of Carbon

Hybridization is the concept of mixing up atomic orbitals into new hybrid orbitals, generally of lower energy and suitable for the pairing of electrons to form chemical bonds.

\({\rm{S}}{{\rm{p}}^{\rm{3}}}\) Hybridisation

The ground state of Carbon has two electrons in its \(2{\rm{s}}\) orbital and \(1\) electron each in \(2{\rm{Px}}\) and \(2{\rm{Py}}\), \(2{\rm{Pz}}\) orbital is empty. However, in its excited state, one paired electron from the \(2{\rm{s}}\) orbital jumps to occupy the empty \(2{\rm{Pz}}\) orbital.

Hence, there are four orbitals, \(2{\rm{s, 2Px, 2Py,}}\) and \(2{\rm{Pz}}\) singly paired orbitals that readily accept an electron from other atoms. This type of overlap of atomic orbitals results in \({\rm{S}}{{\rm{p}}^{\rm{3}}}\) hybridization. It is the presence of these four hybrid orbitals or Sp³ hybridization of the carbon atom that makes it tetravalent.

For example:

In methane \(({\rm{C}}{{\rm{H}}_4})\) there are four \({\rm{S}}{{\rm{p}}^{\rm{3}}}\) hybridized orbitals of Carbon. This is diagrammatically represented as below-

The four hybrid orbitals in methane are located in such a manner so as to decrease the force of repulsion between them.

Nonetheless, the four orbitals do repel each other and get placed at the corners of a tetrahedron. \({\rm{C}}{{\rm{H}}_4}\) has a tetrahedral shape. The \({\rm{s}}{{\rm{p}}^3}\) hybrid orbitals have a bond angle of \({109.5^ \circ }\)

\({\rm{S}}{{\rm{p}}^2}\) Hybridisation

The ground state of Carbon has two electrons in its \(2{\rm{s}}\) orbital and \(1\) electron each in \(2{\rm{Px}}\) and \(2{\rm{Py}}\), \(2{\rm{Pz}}\) orbital is empty. However, in its excited state, one paired electron from the \(2{\rm{s}}\) orbital jumps to occupy the empty \(2{\rm{Pz}}\) orbital.

Hence, there are four orbitals, \(2{\rm{s, 2Px, 2Py,}}\) and \(2{\rm{P}}z,\) singly paired orbitals that readily accept an electron from other atoms. However, there lies a difference in the manner they overlap with each other.

In \({\rm{S}}{{\rm{p}}^{\rm{2}}}\) hybridization, a single electron present in the \(2{\rm{P}}z,\) orbital does not undergo hybridization. Instead, it laterally overlaps with the unhybridized \(2{\rm{P}}z,\) atomic orbital of another carbon atom. This results in the formation of a \({\rm{C}}\,{\rm{ – }}\,{\rm{C}}\) double bond. In a \({\rm{C}}\,{\rm{ – }}\,{\rm{C}}\) double bond:-

1. a sigma \({\rm{(}}\sigma {\rm{)}}\) bond is formed due to the overlap of one \({\rm{S}}{{\rm{p}}^{\rm{2}}}\) orbital of the carbon atom and \(1{\rm{s}}\) orbital of the Hydrogen atom and,
2. a pi \({\rm{(\pi )}}\) bond is formed due to the lateral overlapping of unhybridized \(2{\rm{Pz}}\) orbitals.

For example-

In Ethene \({\rm{(}}{{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{4}}}{\rm{)}}\)

The \(3\) \({\rm{S}}{{\rm{p}}^{\rm{2}}}\) hybrid orbitals in ethene \({\rm{(CH2 = }}\,{\rm{CH2)}}\) form a planar structure with a bond angle of \(120\) degrees.

\({\rm{Sp}}\) Hybridisation

The ground state of Carbon has two electrons in its \(2{\rm{s}}\) orbital and \(1\) electron each in \(2{\rm{Px}}\) and \(2{\rm{Py}}\) orbital. The \(2{\rm{Pz}}\) orbital is empty. However, in its excited state, one paired electron from the \(2{\rm{s}}\) orbital jumps to occupy the empty orbital jumps to occupy the empty \(2{\rm{Pz}}\) orbital.

Hence, there are four orbitals, \(2{\rm{s,}}\,\,{\rm{2Px,}}\,\,{\rm{2Py,}}\) and \(2{\rm{Pz}}\) singly paired orbitals that readily accept an electron from other atoms. However, there lies a difference in the manner they overlap with each other.

In Sp hybridization,  the single electron present in the \(2{\rm{Pz}}\) and \(2{\rm{Py}}\) orbital does not undergo hybridization. Instead, they laterally overlap with the unhybridized \(2{\rm{Pz}}\) and \(2{\rm{Py}}\) atomic orbital of another carbon atom.

This results in the formation of a \({\rm{C}}\,{\rm{ – }}\,{\rm{C}}\) triple bond. In \({\rm{C}}\,{\rm{ – }}\,{\rm{C}}\) triple bond:-

1. a sigma \({\rm{(}}\sigma {\rm{)}}\) bond is formed due to the overlap of one sp orbital of the carbon atom and \({\rm{1s}}\) orbital of the Hydrogen atom,
2. a pi \({\rm{(\pi )}}\) ) bond is formed due to the lateral overlapping of unhybridized \({\rm{2Py}}\) orbitals, and
3. a pi \({\rm{(\pi )}}\) ) bond is formed due to the lateral overlapping unhybridized \({\rm{2Pz}}\) orbitals.

\(2\,{\rm{Sp}}\) hybrid orbitals in ethyne \(({{\rm{C}}_{\rm{2}}}{{\rm{H}}_4})\) form a linear structure with a bond angle of \(180\) degrees.

Left: Tetrahedral carbon (methane), Center: trigonal planar (ethene), Right: linear (acetylene)

Summary

In this article, we learnt-

1. The versatile nature of carbon atoms.
2. Tetravalent nature of Carbon and,
3. Its Hybridization

Also read,

FAQs About Tetravalency of Carbon

Let us look at some of the frequently asked questions about Tetravalency of Carbon:

Q.1. What is the Tetravalence of Carbon atom?
Ans: When an atom has a valency of four, then the element is said to exhibit tetravalency. Tetra stands for four. Group \(14\) elements have \(4\) electrons in their valence shell. Hence they share these four electrons with four other atoms to attain stability.

Q.2. What is the reason for the tetravalency of Carbon?
Ans: The reason behind the tetravalent nature of the carbon atom is that it readily shares its four valence electrons with other atoms. Instead of gaining or losing electrons, it attains stability by sharing electrons. As it shares four electrons, Carbon is said to exhibit tetravalency.

Q.3. Why can’t Carbon lose \(4\) electrons?
Ans: Carbon cannot lose \(4\) electrons because it would require a large amount of energy to remove four electrons and forming a \({{\rm{C}}^{4 + }}\) cation with six protons in its nucleus, holding on to just two electrons.

Q.4. Why does carbon show tetravalency?
Ans: Carbon belongs to group \(14\) of the Periodic table, which means it has four electrons in its valence shell. Carbon can either lose, gain or share electrons to attain the stable noble gas configuration of Neon. But this does not happen because it would require a large amount of energy to remove four electrons and form a \({{\rm{C}}^{4 + }}\) cation, and it would be difficult for the nucleus with six protons to hold on to ten electrons, that is, four extra electrons forming an anion \({{\rm{C}}^{4 – }}\) Hence, a carbon atom can attain stability only by sharing electrons. Thus, it exhibits tetravalency.

Q.5. Why the Valency of Carbon is \(4\)?
Ans: The valency of carbon is \(4\) because it has \(4\) valence electrons and needs \(4\) more electrons to complete its octet configuration and attain stability.

Q.6. What are Tetravalency and Catenation of carbon?
Ans: Tetravalency is the property of an atom to mutually share \(4\) electrons to attain stability. Catenation is the self-linking property of an atom to form long-chain compounds. It is due to the tetravalent and Catenating ability of carbon atom that enables it to form long chains of carbon compounds.

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