CBSE Class 10 Science Notes: Carbon and Its Compounds

Covalent Bonding and Properties

Definition: Covalent bonding involves the sharing of electrons between atoms, primarily non-metals, to achieve a stable electronic configuration (octet rule).

Core Principles:

• Atoms share electrons to attain a full outer shell (like noble gases).
• Forms molecules with relatively weak intermolecular forces.

Basic Properties of Covalent Compounds:

• Generally have low melting and boiling points (due to weak forces).
• Poor conductors of electricity (no free ions or electrons).
• Often soluble in non-polar solvents (like benzene) and less soluble in polar solvents (like water).

Versatility of Carbon

Key Concept: Carbon’s unique ability to form a vast number of compounds stems from its tetravalency (ability to form four bonds) and its capacity to catenate (form chains and rings).

Key Properties:

• Catenation: Carbon atoms can link with each other to form long chains (straight, branched) and rings.
• Multiple Bonding: Carbon can form single, double, and triple bonds with itself and other atoms (e.g., O, N).
• Tetravalency: Carbon’s ability to form four bonds allows for diverse structures.

Hydrocarbons: Saturated and Unsaturated

Definition: Hydrocarbons are organic compounds containing only carbon and hydrogen atoms.

Key Concepts:

• Saturated Hydrocarbons (Alkanes): Single bonds only; general formula $C_nH_{2n+2}$
• Unsaturated Hydrocarbons: Contain at least one double or triple bond.
• Alkenes: Contain at least one carbon-carbon double bond; general formula $C_nH_{2n}$
• Alkynes: Contain at least one carbon-carbon triple bond; general formula $C_nH_{2n-2}$

Examples:

• Alkanes: Methane ($CH_4$), Ethane ($C_2H_6$), Propane ($C_3H_8$)
• Alkenes: Ethene ($C_2H_4$), Propene ($C_3H_6$)
• Alkynes: Ethyne (Acetylene, $C_2H_2$), Propyne ($C_3H_4$)

Homologous Series

Definition: A homologous series is a group of organic compounds with the same functional group and similar chemical properties, where each member differs from the next by a $CH_2$ unit.

Key Features:

• Members have similar chemical properties.
• Each member differs by $CH_2$.
• Show a gradual change in physical properties (e.g., boiling point increases with molecular weight).

Nomenclature Basics

Definition: Naming organic compounds systematically using a set of rules.

Key Rules (Simplified for beginners):

• Alkanes: Prefix (number of carbons) + -ane (e.g., methane – 1 carbon, ethane – 2 carbons)
• Alkenes: Prefix (number of carbons) + -ene (e.g., ethene – 2 carbons, propene – 3 carbons)
• Alkynes: Prefix (number of carbons) + -yne (e.g., ethyne – 2 carbons, propyne – 3 carbons)
• Halogens (e.g., Chlorine, Fluorine): Prefix + “chloro-” , “fluoro-” etc. (e.g., chloromethane, fluoromethane)
• Alcohols: Prefix (number of carbons) + -ol (e.g., methanol, ethanol)
• Aldehydes: Prefix (number of carbons) + -al (e.g., methanal, ethanal)
• Ketones: Prefix (number of carbons) + -one (e.g., propanone, butanone)

Chemical Reactions of Carbon Compounds

Overview: Carbon compounds undergo various chemical reactions.

Combustion:

• Complete Combustion:
  • Products: Carbon dioxide ($CO_2$) and water ($H_2O$)
  • Example: $CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$
  • Relevance: Used for energy production (burning fuels like natural gas, propane).
• Incomplete Combustion:
  • Products: Carbon monoxide ($CO$), carbon (soot, C), and water ($H_2O$)
  • Example: $2CH_4 + 3O_2 \rightarrow 2CO + 4H_2O$
  • Relevance: Occurs with insufficient oxygen; produces toxic carbon monoxide.

Oxidation:

• Example: Ethanol ($C_2H_5OH$) is oxidized to ethanoic acid ($CH_3COOH$).
• This requires an oxidizing agent (e.g., acidified potassium permanganate, $KMnO_4$, or acidified potassium dichromate, $K_2Cr_2O_7$).

Addition Reactions:

• Typical for unsaturated hydrocarbons (alkenes and alkynes).
• A reagent adds to the double or triple bond.
• Example: Ethene ($C_2H_4$) + Hydrogen ($H_2$) $\xrightarrow{Ni/Pt/Pd}$ Ethane ($C_2H_6$)

Substitution Reactions:

• Typical for saturated hydrocarbons (alkanes).
• An atom or group replaces another atom or group.
• Example: Methane ($CH_4$) + Chlorine ($Cl_2$) $\xrightarrow{UV light}$ Chloromethane ($CH_3Cl$) + Hydrogen chloride (HCl). (Multiple chlorination is possible)

Ethanol and Ethanoic Acid

Overview: Important organic compounds with distinct properties and uses.

Ethanol ($C_2H_5OH$):

• Properties: Colorless liquid, volatile, good solvent, miscible with water.
• Uses: Solvent (paints, varnishes), fuel (in some countries, also in some motor fuels), alcoholic beverages.

Ethanoic Acid (Acetic Acid, $CH_3COOH$):

• Properties: Colorless liquid, sour taste, miscible with water.
• Uses: Vinegar (5-8% solution), food preservative, used in the manufacture of various chemical products.

Soaps and Detergents

Definition: Cleaning agents.

How They Clean (Basic Action):

• Soaps/detergents have a long non-polar (hydrophobic) tail and a polar (hydrophilic) head.
• The hydrophobic tail dissolves in grease/oil.
• The hydrophilic head interacts with water, allowing the grease and dirt to be washed away.

Difference Between Soap and Detergent:

• Soaps: Sodium or potassium salts of long-chain fatty acids. Form scum with hard water (containing calcium and magnesium ions).
• Detergents: Synthetic cleaning agents. Generally, they are sulfonates or sulfates. Do not form scum with hard water and are more effective in hard water than soaps.