Carbon and Its Compounds

The Versatile Nature of Carbon

Carbon forms millions of organic compounds due to two unique chemical capabilities:

1. Catenation: The unique ability of carbon to form long, stable covalent bonds with other carbon atoms, producing linear chains, branched networks, and closed ring structures.
2. Tetravalency: Carbon has atomic number $6$ (electronic configuration $2,4$). It requires $4$ electrons to achieve noble gas configuration. It shares $4$ valence electrons with other atoms forming covalent bonds.

Why Carbon Does Not Form $C^{4+}$ or $C^{4-}$ Ions:

• Gaining $4$ electrons ($C^{4-}$): Carbon nucleus ($6$ protons) cannot hold $10$ electrons securely due to immense inter-electronic repulsion.
• Losing $4$ electrons ($C^{4+}$): Requires an exceptionally large amount of ionization energy to overcome nuclear attraction and remove four successive electrons.

Allotropes of Carbon

Homologous Series & Functional Groups

A homologous series is a family of organic compounds having the identical functional group, similar chemical properties, and where successive members differ by a $-\text{CH}_2-$ unit and a molecular mass of $14\text{ u}$.

Major Functional Groups:

• Alcohol ($-\text{OH}$): Methanol ($\text{CH}_3\text{OH}$), Ethanol ($\text{C}_2\text{H}_5\text{OH}$)
• Aldehyde ($-\text{CHO}$): Methanal / Formaldehyde ($\text{HCHO}$), Ethanal ($\text{CH}_3\text{CHO}$)
• Ketone ($-\text{C(=O)}-$): Propanone / Acetone ($\text{CH}_3\text{COCH}_3$)
• Carboxylic Acid ($-\text{COOH}$): Ethanoic acid / Acetic acid ($\text{CH}_3\text{COOH}$)

Important Reactions of Ethanol & Ethanoic Acid

1. Reactions of Ethanol ($\text{C}_2\text{H}_5\text{OH}$):

• Combustion: $\text{C}_2\text{H}_5\text{OH} + 3\text{O}_2 \rightarrow 2\text{CO}_2 + 3\text{H}_2\text{O} + \text{Heat}$
• Reaction with Sodium: $2\text{C}_2\text{H}_5\text{OH} + 2\text{Na} \rightarrow 2\text{C}_2\text{H}_5\text{ONa}\text{ [Sodium Ethoxide]} + \text{H}_2 \uparrow$
• Dehydration with Conc. $H_2SO_4$:

$$\text{CH}_3\text{CH}_2\text{OH} \xrightarrow[\Delta]{443\text{ K},\, \text{Conc. } \text{H}_2\text{SO}_4} \text{CH}_2=\text{CH}_2 + \text{H}_2\text{O}$$

2. Reactions of Ethanoic Acid ($\text{CH}_3\text{COOH}$):

• Esterification (Formation of Sweet-Smelling Ester):

$$\text{CH}_3\text{COOH} + \text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{Acid catalyst}} \text{CH}_3\text{COOC}_2\text{H}_5\text{ [Ethyl Ethanoate]} + \text{H}_2\text{O}$$

• Saponification (Alkaline Hydrolysis of Ester to form Soap):

$$\text{CH}_3\text{COOC}_2\text{H}_5 + \text{NaOH} \rightarrow \text{CH}_3\text{COONa}\text{ [Sodium Acetate]} + \text{C}_2\text{H}_5\text{OH}$$

Cleansing Action of Soaps and Detergents

Soaps are sodium or potassium salts of long-chain fatty acids (e.g., Sodium Stearate: $C_{17}H_{35}COO^-Na^+$).

Structure of a Soap Molecule:

1. Hydrophobic Tail: Long hydrocarbon chain that is water-repelling and oil-soluble.
2. Hydrophilic Head: Ionic carboxylate end ($-COO^-Na^+$) that is water-attracting.

Hydrophobic Tail (dissolves in grease)  ~~~~~~~(O) Hydrophilic Head (dissolves in water)

Micelle Formation:

When soap is dissolved in water, the molecules arrange radially into spherical clusters called micelles:

• The hydrophobic tails point inward, trapping the oily dirt droplet at the core.
• The ionic hydrophilic heads project outward into water, forming a protective ionic sphere.
• Because of negative charge repulsion between ionic heads, micelles do not coalesce and remain suspended as a stable emulsion, easily washed away during rinsing.