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Carbon
Carbon is the seventeenth most abundant element by mass in the Earth's crust and is widely distributed in both free and combined forms. In its elemental state, carbon is found in coal, graphite, and diamond. In its combined state, it exists as metal carbonates, hydrocarbons, and carbon dioxide (0.03%) in the atmosphere. Carbon's versatility makes it one of the most crucial elements in the world.
1.0Introduction
Carbon is undoubtedly the most versatile element, capable of combining with elements like hydrogen, oxygen, chlorine, and sulfur to form a wide range of materials. These include everything from living tissues to pharmaceuticals and plastics, making carbon essential to both biological systems and industrial applications.This versatility is why organic chemistry, a major branch of chemistry, is entirely devoted to carbon-containing compounds. Carbon is an essential constituent of all living organisms.
12C and 13C are two stable naturally occurring isotopesof carbon. Additionally, a third isotope, 14C, is radioactive with a half-life of 5,770 years and is used for radiocarbon dating.
2.0Unique characteristics of Carbon
- Smaller Size and Higher Electronegativity: Carbon differs from other group members due to its smaller atomic size and higher electronegativity.
- Higher Ionization Enthalpy: Carbon has a higher ionisation enthalpy compared to its heavier counterparts.
- Absence of d Orbitals: Carbon lacks available d orbitals, unlike heavier elements in the group, which limits its bonding capabilities.
- Limited Covalence: Carbon can only accommodate four pairs of electrons around it, restricting its maximum covalence to four. However, other group members can expand their covalence due to the presence of d orbitals.
- Ability to Form pπ–pπ Multiple Bonds: Carbon has ability to form pπ–pπ multiple bonds with itself and other tiny, highly electronegative atoms. Examples include C=C, C≡C, C=O, C=S, and C≡N.
- Catenation: Carbon strongly links with other carbon atoms through covalent bonds, forming chains and rings. This property is known as catenation.
- Strength of C—C Bond: The strength of the C—C bond contributes to Carbon's ability to show catenation, which decreases as we move down the group.
- Allotropic Forms: Carbon's ability to form pπ–pπ bonds and its catenation property allows it to exist in various allotropic forms.
3.0Allotropes of Carbon
- Crystalline Forms:
- Diamond: A well-known crystalline form of carbon, characterised by its hardness and high refractive index.
- Graphite is another crystalline form known for its ability to conduct electricity and its use as a lubricant.
- Fullerenes: Discovered in 1985 by H.W. Kroto, E. Smalley, and R.F. Curl, fullerenes represent a third form of Carbon. Fullerenes are composed of carbon atoms arranged in a spherical, tubular, or ellipsoidal shape. The discovery of fullerenes was so significant that Kroto, Smalley, and Curl were awarded the Nobel Prize in Chemistry in 1996.
- Amorphous Forms:
- Carbon also exists in amorphous forms, such as coal, charcoal, and carbon black, which do not have a well-defined crystalline structure.
4.0Form of Carbon Compounds
- Organic Compounds: Organic compounds, often called carbon compounds, are essential to living organisms. They can be synthesised both naturally and in the laboratory. Carbon is a fundamental element in these compounds, which include significant categories such as lipids, carbohydrates, nucleic acids, and proteins.
- Examples: Toluene, benzene, heptane, sucrose.
- Inorganic Compounds: Inorganic carbon compounds can be found in various minerals and natural sources and can be synthesised in the laboratory.
- Examples: Carbonates, oxalates, oxides of carbon, carbon-nitrogen compounds, sulfides of carbon, carboranes, halides of carbon.
- Organometallic Compounds: These compounds contain at least one carbon-metal bond. They are significant in various chemical processes and applications.
- Examples: Ferrocene, tetraethyl lead, Zeise’s salt.
- Carbon Alloys: Carbon is a crucial component in many alloys, created through processes like smelting that involve coke, a form of Carbon. These alloys often contain metals like chromium, aluminium, zinc, and iron.
- Examples: Cast iron, steel.
5.0Chemical Reactions of Carbon
- Combustion Reaction: Carbon reacts with oxygen to produce carbon dioxide, heat, and light. This reaction is the basis of combustion.
- Unsaturated carbon emits a yellow flame and produces soot, while saturated carbon burns with a blue flame. Combustion can be either complete or incomplete.
- Oxidation Reaction: Carbon and its compounds can be oxidised in oxygen, producing carbon monoxide or dioxide.
- Not all oxidation reactions are combustion reactions, and vice versa.
- Addition Reaction: Carbon can form long chains of atoms through addition reactions, converting unsaturated compounds into saturated ones. For example, heating ethene in the presence of hydrogen and a nickel catalyst forms ethane.
CH2=CH2 + H2 + (Nickel Catalyst) → CH3−CH3
- Substitution Reaction: A substitution reaction occurs when one functional group in a compound is replaced with another. For example, methanol and chloride ions are produced in the reaction of methyl chloride with hydroxide.
CH3Cl + OH− → CH3OH + Cl−
These reactions illustrate carbon's versatility in forming various compounds and participating in essential chemical processes.
6.0Uses of Carbon
- Graphite Fibers: Embedded in plastic materials, they form high-strength, lightweight composites used in products like tennis rackets, fishing rods, aircraft, and canoes.
- Graphite:
- Due to its conductivity, graphite is used for electrodes in batteries and industrial electrolysis.
- Graphite crucibles are inert to dilute acids and alkalis, making them suitable for various chemical processes.
- Activated Charcoal: Its high porosity makes it ideal for adsorbing poisonous gases, filtering water to remove organic contaminants, and controlling odours in air conditioning systems.
- Carbon Black: It is used as a black pigment in ink and a filler in automobile tyres to enhance durability.
- Coke: Employed as a fuel and primarily as a reducing agent in metallurgical processes.
- Diamond: Valued as a precious stone, diamonds are widely used in jewellery and are measured in carats (1 carat = 200 mg).