Chapter 4: Carbon and Its Compounds
Introduction
Carbon is a unique element that forms a vast number of compounds, making it essential for life and various industrial applications. It is present in all living organisms and exists in different forms, such as coal, graphite, and diamond. Carbon compounds, especially organic compounds, form the basis of life, including carbohydrates, proteins, fats, and nucleic acids.
Bonding in Carbon – The Covalent Bond
Carbon has an atomic number of 6, which means it has 6 electrons. The electronic configuration of carbon is 2,4, meaning that it has 4 valence electrons in its outermost shell. To achieve stability, carbon needs 4 more electrons to complete its octet (8 electrons in the outer shell).
Why Does Carbon Form Covalent Bonds?
- Carbon cannot lose 4 electrons, as this requires a large amount of energy.
- Carbon cannot gain 4 electrons, as it would become unstable with 10 electrons.
- Instead, carbon shares electrons with other atoms to form covalent bonds.
Example of Covalent Bonding
- Methane (CH₄):
- Carbon shares its 4 electrons with 4 hydrogen atoms to form 4 single covalent bonds.
- Structure:
- Ethene (C₂H₄):
- Two carbon atoms share two pairs of electrons, forming a double bond.
- Structure: H − C = C − H
- Ethyne (C₂H₂):
- Two carbon atoms share three pairs of electrons, forming a triple bond.
- Structure: H − C ≡ C − H
Versatile Nature of Carbon
1. Catenation
Catenation is the property of carbon that allows it to form long chains, branched chains, and rings by bonding with other carbon atoms.
Examples of Catenation:
- Methane (CH₄): 1 Carbon
- Ethane (C₂H₆): 2 Carbons
- Propane (C₃H₈): 3 Carbons
- Cyclohexane (C₆H₁₂): Ring Structure
2. Tetravalency
Carbon has 4 valence electrons, allowing it to form 4 covalent bonds with different elements like hydrogen, oxygen, nitrogen, and chlorine.
Example of Tetravalency:
- Carbon Dioxide (CO₂): Carbon forms two double bonds with oxygen. O = C = O
Saturated and Unsaturated Carbon Compounds
Carbon compounds are classified based on the type of bonding between carbon atoms.
1. Saturated Carbon Compounds (Alkanes)
- These compounds contain only single bonds between carbon atoms.
- General formula: CₙH₂ₙ₊₂
Examples of Alkanes:
- Methane (CH₄)
- Ethane (C₂H₆)
- Propane (C₃H₈)
2. Unsaturated Carbon Compounds
Alkenes: Contain at least one double bond (C=C).
- General formula: CₙH₂ₙ
- Example: Ethene (C₂H₄)
Alkynes: Contain at least one triple bond (C≡C).
- General formula: CₙH₂ₙ₋₂
- Example: Ethyne (C₂H₂)
Chemical Properties of Carbon Compounds
1. Combustion Reaction (Burning of Carbon Compounds)
Carbon compounds burn in oxygen to produce carbon dioxide, water, and energy.
Example:
CH4 + 2O2 → CO2 + 2H2O + Heat
2. Oxidation Reaction
Alcohols can be oxidized to form acids.
Example:
C2H5OH + [O] → CH3COOH + H2O
3. Addition Reaction
Unsaturated hydrocarbons undergo addition reactions, where hydrogen or other elements are added.
Example:
C2H4 + H2 → C2H6
4. Substitution Reaction
Saturated hydrocarbons undergo substitution reactions, where one hydrogen atom is replaced by another element like chlorine.
Example:
CH4 + Cl2 → CH3Cl + HCl
Important Carbon Compounds
1. Ethanol (C₂H₅OH) – Alcohol
- Found in alcoholic beverages, medicines, and fuels.
- Harmful Effects: Affects the nervous system, causes liver damage.
Example of Ethanol Reaction:
- Ethanol reacts with sodium: C2H5OH + Na → C2H5ONa + H2
2. Ethanoic Acid (CH₃COOH) – Acetic Acid
- Found in vinegar, used in food preservatives and medicines.
- Reacts with baking soda to release carbon dioxide gas.
Example:
CH3COOH + NaHCO3 → CH3COONa + H2O + CO2
Soaps and Detergents
1. Soaps
- Made from natural oils and fats + NaOH/KOH.
- Do not work well in hard water (due to calcium & magnesium ions).
Example of Soap Formation (Saponification):
Fat + NaOH → Soap + Glycerol
2. Detergents
- Made from petroleum chemicals, work well in hard water.