Bonding in Carbon - The Covalent Bond

Carbon is a unique element due to its ability to form covalent bonds by sharing electrons with other atoms. In the context of carbon compounds, this property allows it to form strong bonds with itself and other elements, resulting in a wide variety of molecules. Let’s explore how carbon achieves this and the implications for the physical and chemical properties of its compounds.

Why Carbon Forms Covalent Bonds

Carbon has an atomic number of 6, which means its electron configuration is 2, 4. It has four valence electrons in its outermost shell (L shell). To achieve a stable noble gas configuration, carbon needs four more electrons to fill its valence shell, reaching the stable octet configuration.

There are two theoretical possibilities for carbon:

Gaining four electrons to form a $\boldsymbol{\textbf{C}^{4-}}$ anion: This would require gaining four extra electrons, which would create a significant imbalance in charge and is energetically unfavorable.
Losing four electrons to form a $\boldsymbol{\textbf{C}^{4+}}$ cation: This would result in a very unstable cation with only two electrons left, again highly unfavorable.

Instead of losing or gaining electrons, carbon forms covalent bonds by sharing electrons with other atoms, which allows both participating atoms to achieve noble gas configurations.

Types of Covalent Bonds in Carbon Compounds

Carbon can form single, double, or triple covalent bonds, depending on the number of electrons shared between atoms. This gives rise to different types of molecules:

Single Bond: When two atoms share one pair of electrons. Example: Methane ( $\boldsymbol{\textbf{CH}_4}$ ), where carbon shares one electron with each hydrogen atom.

$\boldsymbol{\textbf{CH}_4 \quad (\textbf{Methane})}$
Double Bond: When two atoms share two pairs of electrons. Example: Ethene ( $\boldsymbol{\textbf{C}_2\textbf{H}_4}$ ), where carbon shares two pairs of electrons between two carbon atoms.

$\boldsymbol{\textbf{C}_2\textbf{H}_4 \quad (\textbf{Ethene})}$
Triple Bond: When two atoms share three pairs of electrons. Example: Ethyne ( $\boldsymbol{\textbf{C}_2\textbf{H}_2}$ ), where there are three shared pairs of electrons between two carbon atoms.

$\boldsymbol{\textbf{C}_2\textbf{H}_2 \quad (\textbf{Ethyne})}$

Each of these bonding configurations results in different chemical properties, such as reactivity and stability.

Electron Dot Structures

To visualize the covalent bonding in carbon compounds, we use electron dot structures. These diagrams represent the valence electrons of atoms as dots and help depict how atoms share electrons.

For example, the electron dot structure of methane ( $\boldsymbol{\textbf{CH}_4}$ ) shows carbon in the center, sharing electrons with four hydrogen atoms:

$\boldsymbol{\textbf{H} \cdot \textbf{C} \cdot \textbf{H}}$

Here, each dot represents a shared electron pair forming a covalent bond.

Properties of Covalent Compounds

Low Melting and Boiling Points: Covalent compounds generally have low melting and boiling points compared to ionic compounds because the intermolecular forces between covalent molecules are weak.
Poor Conductors of Electricity: Since covalent compounds do not form ions, they do not conduct electricity in either solid or molten states.
Solubility: Most covalent compounds are soluble in non-polar solvents like benzene but are insoluble in water (a polar solvent).

Real-life Applications

Hydrocarbons as Fuels: Covalent compounds like methane ( $\boldsymbol{\textbf{CH}_4}$ ), ethane ( $\boldsymbol{\textbf{C}_2\text{H}_6}$ ), and propane ( $\boldsymbol{\textbf{C}_3\text{H}_8}$ ) are widely used as fuels in domestic and industrial applications due to their ability to release a significant amount of energy when combusted.
Organic Chemistry: Covalent bonding in carbon forms the basis of organic chemistry, which studies millions of carbon compounds essential to life and industry. Pharmaceuticals, plastics, and even food items are based on covalent compound.

Practice Questions with Answers

Q1: Draw the electron dot structure of methane (CH₄) and explain how the covalent bond is formed.

Answer: In methane, carbon shares one electron with each hydrogen atom. The electron dot structure shows carbon in the center with dots representing shared electron pairs.
- $\boldsymbol{\textbf{H} \cdot \textbf{C} \cdot \textbf{H}}$

Q2 Explain why covalent compounds generally have low melting and boiling points.

Answer: Covalent compounds have low melting and boiling points because the forces of attraction between the molecules (intermolecular forces) are weak, requiring less energy to break.