Introduction
Carbon compounds are substances that contain carbon atoms bonded with other carbon atoms or with elements such as hydrogen, oxygen, nitrogen, sulfur, and halogens. Carbon forms a large number of compounds because of its unique properties like catenation and tetravalency.
The physical and chemical properties of carbon compounds make them useful in fuels, medicines, plastics, food, textiles, and many industrial products.
Why Carbon Compounds are Unique?
Carbon compounds possess special characteristics because:
- Carbon is tetravalent (valency = 4).
- Carbon forms strong covalent bonds.
- Carbon shows catenation (self-linking property).
- Carbon can form single, double, and triple bonds.
- Carbon compounds can exist as straight chains, branched chains, and rings.
Physical Properties of Carbon Compounds
1. Low Melting and Boiling Points
Most carbon compounds have relatively low melting and boiling points because they are covalent compounds.
Examples
| Compound | Boiling Point |
|---|---|
| Methane | -161.5°C |
| Ethanol | 78°C |
| Propane | -42°C |
Reason
- Covalent molecules have weak intermolecular forces.
- Less energy is required to separate molecules.
2. Poor Conductors of Electricity
Most carbon compounds do not conduct electricity.
Reason
- Covalent compounds do not produce free ions.
- Absence of mobile charged particles prevents electrical conduction.
Examples
- Methane
- Ethane
- Ethanol
- Benzene
Exception
Graphite conducts electricity due to the presence of free electrons.
3. Insoluble in Water
Most carbon compounds are insoluble or only slightly soluble in water.
Reason
- Carbon compounds are generally non-polar.
- Water is a polar solvent.
- “Like dissolves like” principle applies.
Examples
| Soluble in Water | Insoluble in Water |
|---|---|
| Ethanol | Benzene |
| Acetic Acid | Kerosene |
| Glucose | Petrol |
4. Soluble in Organic Solvents
Carbon compounds dissolve easily in organic solvents.
Common Organic Solvents
- Benzene
- Ether
- Chloroform
- Acetone
Chemical Properties of Carbon Compounds
1. Combustion
Carbon compounds burn in oxygen to produce carbon dioxide, water, heat, and light.
General Equation
Carbon Compound + Oxygen → Carbon Dioxide + Water + Heat
Example
Methane combustion:
CH₄ + 2O₂ → CO₂ + 2H₂O + Heat
Characteristics
- Produces heat and light.
- Used as fuels.
- Complete combustion gives a blue flame.
2. Oxidation
Carbon compounds can be oxidized in the presence of oxidizing agents.
Common Oxidizing Agents
- Alkaline potassium permanganate (KMnO₄)
- Acidified potassium dichromate (K₂Cr₂O₇)
Example
Ethanol → Ethanoic Acid
3. Addition Reaction
Unsaturated hydrocarbons undergo addition reactions.
Example
Ethene + Hydrogen → Ethane
C₂H₄ + H₂ → C₂H₆
Conditions
- Nickel or Palladium catalyst
- Heating
This process is called hydrogenation.
Uses
- Conversion of vegetable oils into vanaspati ghee.
4. Substitution Reaction
Saturated hydrocarbons undergo substitution reactions.
Example
CH₄ + Cl₂ → CH₃Cl + HCl
Conditions
- Presence of sunlight
In this reaction, hydrogen atoms are replaced by chlorine atoms.
Important Properties of Carbon Compounds
| Property | Description |
|---|---|
| Covalent Nature | Carbon compounds are mainly covalent. |
| Low Melting Point | Weak intermolecular forces. |
| Low Boiling Point | Less energy required for separation. |
| Poor Electrical Conductivity | No free ions present. |
| Insoluble in Water | Mostly non-polar compounds. |
| Soluble in Organic Solvents | Similar molecular nature. |
| Combustible | Burn easily in oxygen. |
| Oxidizable | Can undergo oxidation reactions. |
| Addition Reactions | Seen in unsaturated hydrocarbons. |
| Substitution Reactions | Seen in saturated hydrocarbons. |
NCERT Key Points for Revision
- Carbon compounds are mainly covalent compounds.
- They generally have low melting and boiling points.
- Most carbon compounds are poor conductors of electricity.
- They are usually insoluble in water but soluble in organic solvents.
- Carbon compounds undergo combustion and oxidation reactions.
- Unsaturated hydrocarbons show addition reactions.
- Saturated hydrocarbons show substitution reactions.
- Carbon compounds are important fuels and industrial chemicals.
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Practice Questions
Short Answer Questions
1. Why do carbon compounds have low melting and boiling points?
Answer:
Because carbon compounds are covalent compounds with weak intermolecular forces.
2. Why do most carbon compounds not conduct electricity?
Answer:
They do not contain free ions or free electrons for electrical conduction.
3. What is combustion?
Answer:
Combustion is the process in which a substance burns in oxygen producing heat and light.
4. What is hydrogenation?
Answer:
Hydrogenation is the addition of hydrogen to unsaturated hydrocarbons in the presence of a catalyst.
5. Name two oxidizing agents used for carbon compounds.
Answer:
- Potassium permanganate (KMnO₄)
- Potassium dichromate (K₂Cr₂O₇)
Fill in the Blanks
- Carbon compounds are mainly __________ compounds.
Answer: Covalent - Most carbon compounds are poor conductors of __________.
Answer: Electricity - Ethene undergoes __________ reaction.
Answer: Addition - Methane burns in oxygen to form carbon dioxide and __________.
Answer: Water - Saturated hydrocarbons generally undergo __________ reactions.
Answer: Substitution - Carbon compounds are usually insoluble in __________.
Answer: Water - Carbon exhibits __________ due to self-linking property.
Answer: Catenation - Ethanol can be oxidized into __________ acid.
Answer: Ethanoic - Complete combustion generally produces a __________ flame.
Answer: Blue - Carbon has a valency of __________.
Answer: Four
MCQs (Multiple Choice Questions)
1. Carbon compounds are mainly:
A. Ionic
B. Metallic
C. Covalent
D. Electrovalent
Answer: C. Covalent
2. Most carbon compounds have:
A. High melting points
B. Low melting points
C. Infinite melting points
D. No melting points
Answer: B. Low melting points
3. Which carbon allotrope conducts electricity?
A. Diamond
B. Coal
C. Graphite
D. Coke
Answer: C. Graphite
4. Carbon compounds are generally insoluble in:
A. Benzene
B. Ether
C. Chloroform
D. Water
Answer: D. Water
5. Combustion of methane produces:
A. CO₂ and H₂O
B. H₂ and O₂
C. CO and H₂
D. CH₄ and O₂
Answer: A. CO₂ and H₂O
6. Ethene belongs to:
A. Saturated hydrocarbon
B. Alkane
C. Unsaturated hydrocarbon
D. Cycloalkane
Answer: C. Unsaturated hydrocarbon
7. Hydrogenation is an example of:
A. Substitution reaction
B. Addition reaction
C. Oxidation reaction
D. Neutralization reaction
Answer: B. Addition reaction
8. Methane undergoes:
A. Addition reaction
B. Substitution reaction
C. Decomposition reaction
D. Neutralization reaction
Answer: B. Substitution reaction
9. Which oxidizing agent is commonly used in NCERT?
A. NaCl
B. HCl
C. KMnO₄
D. NaOH
Answer: C. KMnO₄
10. The valency of carbon is:
A. 1
B. 2
C. 3
D. 4
Answer: D. 4
Conclusion
The properties of carbon compounds arise mainly due to their covalent nature. They generally have low melting and boiling points, are poor conductors of electricity, and are insoluble in water. Chemically, they undergo combustion, oxidation, addition, and substitution reactions. These properties make carbon compounds essential in daily life, industry, medicine, fuels, and biological systems.