Carbon: Allotropes, Compounds, Fuels, and Organic Chemistry Basics

TAKEAWAYS:

• Carbon forms four covalent bonds due to its valency of 4, leading to diverse structures like chains, rings, and networks.
• Allotropes (diamond, graphite, fullerenes) show how carbon’s bonding affects properties—hardness, conductivity, and shape.
• Carbon oxides (CO, CO₂) and carbonates are crucial in industry, respiration, and environmental chemistry (e.g., global warming).
• Fossil fuels (coal, petroleum, natural gas) are carbon-based energy sources with environmental trade-offs.
• Organic chemistry revolves around carbon’s ability to catenate (form long chains) and bond with H, O, N, etc.
• NEB exam focus: Identify allotropes, write balanced equations for combustion/reactions, and explain carbon’s role in fuels and life.

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Carbon: The Element of Life and Industry

Carbon is the 4th most abundant element in the universe and the backbone of all life on Earth. It is found in fossil fuels, diamonds, graphite, and every organic compound (from sugars to plastics). Its unique ability to form strong covalent bonds in straight chains, branched chains, and rings makes it the most versatile element.

Why is Carbon Special?

Carbon has 4 valence electrons, allowing it to form four covalent bonds with other atoms (e.g., hydrogen, oxygen, nitrogen). This leads to:

1. Catenation: Carbon atoms can bond with other carbon atoms to form long chains or rings (e.g., alkanes, benzene).
2. Versatility: It bonds with H, O, N, S, halogens, creating millions of compounds.
3. Stability: C-C and C-H bonds are strong and unreactive, making organic compounds durable.

Carbon’s electron configuration explains its bonding behavior.

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Allotropes of Carbon: Same Element, Different Forms

Allotropes are different forms of the same element with distinct properties. Carbon has three main allotropes:

1. Diamond: Hardest natural substance, used in jewelry and cutting tools.
2. Graphite: Soft, conducts electricity, used in pencils and electrodes.
3. Fullerenes: Hollow molecules (e.g., C₆₀ "buckyballs"), used in nanotechnology.

1. Diamond

• Structure: Each carbon atom is tetrahedrally bonded to 4 others in a 3D network.
• Properties:
  • Hardest known material (10 on Mohs scale).
  • Does not conduct electricity (no free electrons).
  • High melting point (3550°C).
• Uses: Jewelry, industrial cutting, heat sinks.

2. Graphite

• Structure: Carbon atoms form layers of hexagons, with weak forces between layers.
• Properties:
  • Soft and slippery (layers slide over each other).
  • Conducts electricity (delocalized electrons in layers).
  • Lubricant and moderator in nuclear reactors.
• Uses: Pencils, electrodes, lubricants.

3. Fullerenes (e.g., C₆₀)

• Structure: Hollow soccer-ball-shaped molecules (60 carbon atoms in hexagons and pentagons).
• Properties:
  • Nanoscale size (1 nm diameter).
  • Conducts electricity (like graphite but in molecules).
  • Superstrong and lightweight.
• Uses: Drug delivery, lubricants, superconductors.

Comparison Table: Allotropes of Carbon

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Carbon Compounds: Oxides and Carbonates

1. Carbon Monoxide (CO)

• Formation: Incomplete combustion of carbon/fuels. mermaid flowchart TD A[Dead Plants/Animals] --> B[Heat & Pressure Over Millions of Years] B --> C[Coal] B --> D[Petroleum] D --> E[Refining] E --> F[Gasoline\nDiesel\nKerosene] B --> G[Natural Gas] G --> H[CH4\nCleaner Fuel]

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## Carbon in Organic Chemistry
Organic chemistry is the study of **carbon compounds**, which include:
- **Hydrocarbons**: Only C and H (e.g., methane \( CH_4 \), ethane \( C_2H_6 \)).
- **Functional groups**: Atoms/groups that determine reactivity (e.g., -OH in alcohols, -COOH in acids).

### Key Concepts:
1. **Homologous Series**: Families of organic compounds with the **same functional group** and similar properties (e.g., alkanes: \( C_nH_{2n+2} \)).
2. **Isomerism**: Compounds with the **same formula but different structures** (e.g., butane and isobutane).
   figure
{"type":"curves","lines":[{"label":"CO₂ Levels","from":[1950,315],"to":[2020,415],"trend":"up"}],"xlabel":"Year","ylabel":"CO₂ (ppm)","caption":"Rising CO₂ levels since 1950"}

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NEB Exam Tips for Unit 12

1. Allotropes: Know the structure, properties, and uses of diamond, graphite, and fullerenes. Draw their structures.
2. Equations: Balance equations for:
   • Combustion of carbon (CO and CO₂ formation).
   • Carbonates + acids (e.g., $CaC{O}_3+HCl$).
3. Fossil Fuels: Explain formation, refining, and environmental impact.
4. Organic Basics: Recognize homologous series, isomers, and functional groups.
5. Diagrams: Label diagrams of fractional distillation, allotropes, and molecular structures.

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NEB-Style Questions (Practice)

Short Answer (5 marks)

1. Describe the structure and uses of graphite. Why is it a good lubricant?
2. Write the balanced equation for the reaction between calcium carbonate and hydrochloric acid. What gas is evolved?
3. What are homologous series? Give an example with two members.

Long Answer (10 marks)

4. Explain how coal, petroleum, and natural gas are formed. Discuss their advantages and disadvantages as energy sources.
5. With labeled diagrams, compare the structure and properties of diamond and graphite. Why does diamond not conduct electricity while graphite does?

Practical (5 marks)

6. A student burns 12 g of carbon in limited oxygen and collects 22 g of CO. Calculate:
   • The mass of oxygen used.
   • The mass of CO₂ that would form if oxygen were in excess.

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Answer Key for Practice:

1. Graphite has hexagonal layers with weak forces between them, making it soft and slippery (good lubricant). Uses: pencils, electrodes.
2. $CaC{O}_3+2HCl\to CaC{l}_2+C{O}_2+H_{2}O$. Gas evolved: CO₂.
3. Homologous series: Family of organic compounds with the same functional group and general formula differing by $C{H}_2$. Example: Alkanes ($C_n{H}_{2n+2}$): methane ($C{H}_4$), ethane ($C_2{H}_6$).
4. See note for formation details. Advantages: energy-rich; disadvantages: pollution, non-renewable.
5. Diamond: 3D tetrahedral network, hard, non-conductive. Graphite: hexagonal layers, soft, conductive (delocalized electrons).
6. Using $C+O_2\to C{O}_2$ and $2C+O_2\to 2CO$:
   • Moles of CO = 22 g / 28 g/mol = 0.786 mol.
   • Mass of O used = (0.786 × 16) g = 12.58 g.
   • For excess O₂: 12 g C → 12/12 = 1 mol C → 1 mol CO₂ → 44 g CO₂.

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Final Note: Carbon is the building block of life and industry. Master its allotropes, compounds, fuels, and organic chemistry basics to excel in NEB exams! Practice drawing structures and balancing equations regularly.