Carbon and Its Compounds

1. Introduction

Carbon is one of the most important elements in chemistry. A very large number of compounds contain carbon, including substances present in living organisms, fuels, medicines, plastics, fibres and many household products.

The ability of carbon to form strong covalent bonds with itself and with other elements allows it to form an enormous variety of compounds.

2. Covalent Bond

A covalent bond is formed when atoms share electrons. Carbon generally forms covalent bonds because it has four valence electrons and does not easily gain or lose four electrons to form a stable ion.

Why Does Carbon Form Covalent Bonds?

Carbon has atomic number 6 and electronic configuration 2,4. It needs four more electrons to complete its outer shell. Losing or gaining four electrons would require a very large amount of energy, so carbon generally achieves stability by sharing electrons.

Example: Methane

In methane, carbon shares electrons with four hydrogen atoms to form four covalent bonds.

3. Electron Dot Structures

Electron dot structures represent valence electrons using dots around the chemical symbols. They help us understand how atoms share electrons to form covalent bonds.

Important Molecules

• Hydrogen (H₂)
• Oxygen (O₂)
• Nitrogen (N₂)
• Methane (CH₄)
• Ethane (C₂H₆)

4. Properties of Covalent Compounds

• Covalent compounds generally have low melting and boiling points compared with many ionic compounds.
• Many covalent compounds are poor conductors of electricity because they do not contain freely moving ions.
• Many molecular covalent compounds are soluble in organic solvents rather than water, although solubility varies greatly with molecular structure.

5. Versatile Nature of Carbon

Carbon shows two major properties that allow the formation of a huge number of compounds: tetravalency and catenation.

Tetravalency

Carbon has valency four. It can therefore form four covalent bonds with the same or different atoms.

Catenation

Catenation is the ability of carbon atoms to form bonds with other carbon atoms, producing chains, branched structures and rings.

6. Hydrocarbons

Compounds made up of carbon and hydrogen only are called hydrocarbons.

Saturated Hydrocarbons

Hydrocarbons containing only carbon-carbon single bonds are called saturated hydrocarbons.

Unsaturated Hydrocarbons

Hydrocarbons containing one or more carbon-carbon double or triple bonds are called unsaturated hydrocarbons.

7. Alkanes, Alkenes and Alkynes

8. Homologous Series

A homologous series is a family of organic compounds having the same functional group and similar chemical properties, in which successive members differ by a –CH₂– unit.

9. Nomenclature of Carbon Compounds

Systematic naming helps identify organic compounds based on their carbon chain and functional groups.

Common Carbon Roots

10. Functional Groups

A functional group is an atom or group of atoms that gives an organic compound its characteristic chemical properties.

11. Ethanol

Ethanol is an alcohol with the molecular formula C₂H₅OH. It contains the –OH functional group.

Oxidation of Ethanol

Ethanol can be oxidised to ethanoic acid using suitable oxidising agents.

Uses

• Used as a solvent.
• Used in medicines and laboratory products.
• Used as a fuel or fuel component in suitable applications.

12. Ethanoic Acid

Ethanoic acid is a carboxylic acid with the formula CH₃COOH. Its dilute aqueous solution is commonly known as vinegar.

Reaction with Sodium Hydrogen Carbonate

Esterification

Ethanoic acid reacts with an alcohol in the presence of a suitable acid catalyst to form an ester and water.

Esters often have pleasant fruity smells and are used in perfumes and flavouring materials.

13. Chemical Properties of Carbon Compounds

Combustion

Carbon compounds generally burn in oxygen to produce carbon dioxide and water, releasing energy when combustion is complete.

Oxidation

Certain carbon compounds can be oxidised by suitable oxidising agents.

Addition Reaction

Unsaturated compounds can undergo addition reactions in which atoms are added across double or triple bonds.

Substitution Reaction

Saturated hydrocarbons can undergo substitution reactions in which one atom or group is replaced by another.

14. Soaps and Detergents

Soap

Soaps are generally sodium or potassium salts of long-chain fatty acids.

Cleansing Action

Soap molecules contain a water-attracting ionic end and a hydrocarbon end that interacts with oily dirt. In water, soap molecules form structures called micelles that help surround and remove grease and dirt.

Micelles

In a micelle, the hydrophobic hydrocarbon tails point toward oily material while the hydrophilic ends remain associated with water.

Problem with Hard Water

Soap reacts with calcium and magnesium ions present in hard water to form insoluble substances called scum. This reduces cleansing efficiency.

Detergents

Detergents are synthetic cleansing agents that generally do not form insoluble scum with calcium and magnesium ions in the same way as ordinary soaps. They therefore work better in hard water.

15. Saturated and Unsaturated Compounds

16. Important Formulae

17. Quick Revision

Official Study Sources

Use the official NCERT textbook and current CBSE Academic resources for curriculum-aligned study.