1. Bonding in Carbon

Chapter 4

Carbon & its Compounds

Introduction

Covalent Bond: The atomic number of carbons is 6. Its electronic configuration is 2, 4. It requires, 4 electrons to achieve the inert gas electronic configuration. But carbon cannot form an ionic bond.
 It could gain four electrons forming C^4- cation. But it would be difficult for the nucleus with six protons to hold on to ten electrons.
It could lose four electrons forming C⁴⁺ cations. But it requires a large amount of energy to remove four electrons.
Thus, carbon overcomes this problem by sharing of its valence electrons with other carbon atoms or with atoms of other elements.
The bond formed by mutual sharing of electron pairs between two atoms in a molecule is known as Covalent Bond.

Types of Covalent Bond:
Single Covalent Bond: When a single pair of electrons are shared between two atoms in a molecule. For example; F₂, Cl₂, H₂ etc.
The atomic number of hydrogen is 1. Hence it has one electron in its K shell and it requires one more electron to fill the K shell. So, two hydrogen atoms share their electrons to form a molecule of hydrogen, H₂.

Double Covalent Bond: When two pairs of electrons are shared between two atoms in a molecule. For example; O₂, CO₂ etc.
The atomic number of oxygen is 8. So it has six electrons in its L shell and it requires two more electrons to complete its octet. So each atom of oxygen shares two electrons with another atom of oxygen. The two electrons contributed by each oxygen atom give rise to a double bond between the two atoms.

Triple Covalent Bond: When three pairs of electrons are shared between two atoms in a molecule. For example; N₂ etc.
Nitrogen has the atomic number 7. So, it has five electrons in its L shell and it requires three more electrons to complete its octet. So, in order to attain an octet, each nitrogen atom in a molecule of nitrogen contributes three electrons giving rise to three shared pairs of electrons that results in a triple bond between the two atoms.

Allotropes of Carbon

• Different forms of an element that have same chemical properties but different physical properties are known as Allotropes.
• There are three allotropes of carbon - Diamond, graphite and Fullerene

(i) Diamond
In diamond, each carbon atom is bonded to four other carbon atoms forming a rigid three-dimensional structure.
→ It is the hardest substance known.
→ It has high melting point.
→ It is a bad conductor of electricity.
→ It is used in making jewellery. It is also used in cutting and drilling tools.

(ii) Graphite
→ Each carbon atom is bonded with other three carbon atoms in the same plane forming hexagonal rings.
→ These rings are stacked over each other through weak Van der Waals forces.
→ Graphite is also a very good conductor of electricity.
→ It is used as dry lubricant.
→ It is used in making pencil lead.

(iii) Fullerene
→ C₆₀, also known as Buck minster fullerene, is the most common form of fullerenes.
→ It has carbon atoms arranged in the shape of a football.
→ It consists of 60 carbon atoms arranged in 12 pentagons and 20 hexagons.

Versatile nature of carbon
Carbon is included in ten formations of a variety of compounds. This is due to the following two reasons:
(i) Catenation: Carbon has the unique ability to form covalent bonds with other atoms of carbon, giving rise to large molecules. This property is called catenation.
Carbon exhibits catenation property due to the following reasons:
→ Size of the carbon atom is very small. This enables its nucleus to hold the shared pair of electrons strongly.
→ The carbon-carbon bond is quite strong.
(ii) Tetravalent Nature: Since carbon has a valency of four, it is capable of bonding with four other atoms of carbon or atoms of some other mono-valent element.