Carbon and its Compounds
1. Bonding in Carbon
Carbon is a unique element in the periodic table due to its ability to form covalent bonds. It has four valence electrons, allowing it to share electrons with other elements to achieve stability.
Formation of Covalent Bond: Covalent bonding involves the sharing of electrons between atoms. These atoms can be either identical or different elements. Unlike ionic bonding, where electrons are transferred, covalent bonding ensures both atoms achieve a stable electronic configuration.
Covalency: The number of electrons an atom shares to form covalent bonds is known as its covalency. Carbon has a covalency of four, meaning it forms four covalent bonds with other atoms.
Characteristics of Covalent Compounds
- Covalent compounds are molecular in nature and exist as discrete molecules.
- They generally have lower melting and boiling points compared to ionic compounds due to weak intermolecular forces.
- These compounds are typically insoluble in water but dissolve in organic solvents like benzene, kerosene, and petrol.
- Covalent compounds do not conduct electricity, as they lack free-moving electrons or ions.
2. Allotropy in Carbon
Allotropy refers to the ability of an element to exist in multiple forms with different physical properties while maintaining the same chemical properties. Carbon exhibits allotropy in both crystalline and amorphous forms.
- Crystalline Allotropes: Diamond and graphite are the most well-known crystalline allotropes.
- Diamond: In diamond, each carbon atom forms strong covalent bonds with four other carbon atoms, resulting in a rigid three-dimensional structure. Diamond is the hardest known natural substance and is used in cutting tools and jewelry.
- Graphite: Graphite consists of hexagonal layers of carbon atoms. Each carbon atom forms bonds with three neighboring atoms, leaving free electrons that make graphite a good conductor of electricity. It is used in pencils, lubricants, and electrodes.
- Amorphous Allotropes: These include coal, charcoal, and lamp black.
- Coal: Coal is a naturally occurring carbon-rich substance used as a fuel.
- Charcoal: Charcoal is produced by heating wood in the absence of oxygen. It has high porosity and is used for filtration and fuel.
- Lamp Black: A fine black powder produced by burning hydrocarbons, commonly used in inks and paints.
- Fullerenes: Fullerenes are a distinct class of carbon allotropes. The first discovered fullerene was C60, which forms a spherical structure resembling a football. Fullerenes have promising applications in nanotechnology.
3. Unique Nature of Carbon
Carbon’s versatility arises due to the following properties:
- Catenation: Carbon has the unique ability to form long chains and rings by bonding with other carbon atoms through covalent bonds. The extent of catenation depends on the strength of these bonds.
- Variable Oxidation States: Carbon exhibits multiple oxidation states, allowing it to form diverse compounds.
- Formation of Multiple Bonds: Carbon can form single, double, and triple bonds, leading to the classification of saturated and unsaturated compounds.
4. Saturated and Unsaturated Carbon Compounds
Saturated Compounds: These compounds contain only single bonds between carbon atoms. Examples include alkanes like methane (CH4) and ethane (C2H6).
Unsaturated Compounds: These compounds contain double or triple bonds between carbon atoms, making them more reactive than saturated compounds. Examples include alkenes (ethylene, C2H4) and alkynes (acetylene, C2H2).
5. Classification of Carbon Compounds
Straight Chain Compounds
These compounds feature a continuous, linear sequence of carbon atoms. Examples include normal butane (C4H10) and normal pentane (C5H12).
Branched Chain Compounds
Compounds that exhibit branching in their carbon skeleton. Examples include iso-butane (C4H10) and neopentane (C5H12).
Closed Chain or Ring Compounds
Cyclic compounds containing carbon atoms arranged in a ring structure, e.g., cyclohexane (C6H12) and benzene (C6H6).
6. Hydrocarbons
Compounds containing only carbon and hydrogen atoms are called hydrocarbons. They are further classified into alkanes, alkenes, and alkynes.
7. Functional Groups
A functional group is an atom or group of atoms that determine the properties of a compound. Examples include:
- Hydroxyl (-OH) for alcohols
- Carboxyl (-COOH) for acids
- Aldehyde (-CHO) for aldehydes
- Ketone (-CO-) for ketones
8. Homologous Series
A series of organic compounds where each member differs by a fixed -CH2- unit. Examples include alkanes, alcohols, and acids.
9. Chemical Properties of Carbon Compounds
- Combustion: Carbon compounds burn in oxygen to release CO2 and water with heat and light.
- Oxidation: Carbon compounds undergo oxidation using oxidizing agents like KMnO4.
- Addition Reaction: Unsaturated hydrocarbons react with halogens and hydrogen.
- Substitution Reaction: Saturated hydrocarbons undergo substitution reactions in the presence of catalysts.
10. Important Carbon Compounds
Examples include alcohols like ethanol (C2H5OH) and acids like acetic acid (CH3COOH).
11. Soaps and Detergents
Soaps: Sodium salts of long-chain carboxylic acids used for cleansing.
Detergents: Sulfate or ammonium salts of hydrocarbons used for washing purposes.