Chapter 4: Carbon and its Compounds

4.1 Bonding in Carbon – The Covalent Bond

Covalent Bonds: Carbon compounds feature covalent bonding, resulting in weak intermolecular forces. Consequently, they exhibit low melting and boiling points compared to ionic compounds.
Electrical Conductivity: Because electrons are shared and no ions or charged particles are formed, carbon compounds are generally poor conductors of electricity.

Electronic Configuration: Carbon has an atomic number of 6, with 4 valence electrons in its outermost shell, meaning it must share electrons to attain a stable noble gas configuration.
Anion Difficulty (C4-): Gaining 4 electrons to form a C4- anion is energetically unfavorable, as a nucleus with 6 protons cannot easily hold 10 electrons.
Cation Difficulty (C4+): Losing 4 electrons to form a C4+ cation requires a massive amount of energy to overcome the nuclear attraction of 6 protons holding onto just 2 remaining electrons.

Single Covalent Bond: Formed by sharing one pair of electrons between two atoms (e.g., in hydrogen molecules, H2, or chlorine, Cl2).
Double Covalent Bond: Formed by sharing two pairs of electrons between adjacent atoms (e.g., in oxygen molecules, O2).
Triple Covalent Bond: Formed by sharing three pairs of electrons (e.g., in nitrogen molecules, N2).
Tetravalency: Carbon is tetravalent, allowing it to form covalent bonds with up to four other atoms, such as in methane (CH4).

Diamond: Each carbon atom is bonded to four other carbon atoms in a rigid, three-dimensional network, making it the hardest known substance.
Graphite: Carbon atoms are arranged in hexagonal arrays in parallel layers. Since each carbon is bonded to three others, one free valence electron per atom allows graphite to conduct electricity.
Fullerenes: Allotropes where carbon atoms are arranged in geodesic spheres, with the first identified being Buckminsterfullerene (C-60), resembling a football.

4.2 Versatile Nature of Carbon

Catenation: The unique ability of carbon to form stable covalent bonds with other carbon atoms, giving rise to incredibly long chains, branches, or rings.
Bond Stability: Carbon-carbon bonds are exceptionally strong and stable due to carbon's small atomic size, allowing the nucleus to hold shared pairs securely.

Saturated Compounds: Carbon chains linked entirely by single bonds, also known as alkanes (e.g., methane, ethane), which are generally less reactive.
Unsaturated Compounds: Carbon chains containing one or more double bonds (alkenes) or triple bonds (alkynes), making them significantly more reactive.

Structural Isomers: Compounds that share the exact same molecular formula but possess different structural arrangements (e.g., butane and isobutane, both C4H10).
Cyclic Compounds: Hydrocarbons arranged in rings, which can be saturated (e.g., cyclohexane, C6H12) or unsaturated (e.g., benzene, C6H6).

Heteroatom: Elements other than carbon and hydrogen (such as Cl, Br, O, N, S) that substitute for hydrogen in a hydrocarbon chain.
Functional Groups: Particular clusters of heteroatoms that confer distinct chemical properties to the organic molecule, including alcohol (-OH), aldehyde (-CHO), ketone (-CO-), and carboxylic acid (-COOH).

Homologous Series: A family of carbon compounds sharing the same functional group and general formula, where successive members differ by a -CH2- unit (and 14 u in molecular mass).
Gradation in Properties: Physical characteristics like melting and boiling points increase systematically with molecular mass, whereas chemical properties remain highly similar due to the identical functional group.

IUPAC Nomenclature: The scientific system used to name organic molecules by identifying the longest carbon chain parent name and adding a prefix or suffix corresponding to its functional group.

4.3 Chemical Properties of Carbon Compounds

Combustion: An oxidation reaction where carbon and its compounds burn in oxygen to yield carbon dioxide, water vapor, heat, and light.
Flame Characteristics: Saturated hydrocarbons typically burn with a clean, blue flame. Unsaturated compounds produce a yellow, sooty flame due to incomplete combustion.

Oxidation: While combustion is complete oxidation, controlled reactions can convert alcohols into carboxylic acids using powerful oxidising agents like alkaline potassium permanganate (KMnO4) or acidified potassium dichromate (K2Cr2O7).

Addition Reaction: Unsaturated hydrocarbons combine with hydrogen in the presence of metallic catalysts (like nickel or palladium) to form saturated hydrocarbons. This process is commercially applied in the hydrogenation of vegetable oils.

Substitution Reaction: Saturated hydrocarbons, which are typically inert, react with chlorine in the presence of sunlight, replacing hydrogen atoms one by one.

4.4 Key Carbon Compounds: Ethanol and Ethanoic Acid

Ethanol: A liquid at room temperature, commonly known as alcohol, which serves as an outstanding solvent in industrial applications and medicines.
Sodium Reaction: Ethanol reacts with sodium metal to produce hydrogen gas and sodium ethoxide.
Dehydration: Heating ethanol to 443 K with excess concentrated sulfuric acid (acting as a dehydrating agent) yields ethene and water.
Denatured Alcohol: Ethanol mixed with poisonous additives like methanol and colored dyes to prevent illegal consumption in industrial workspaces.

Ethanoic Acid: Also known as acetic acid, a weak carboxylic acid. A 5-8% solution of this acid in water is sold commercially as vinegar.
Glacial Acetic Acid: Pure ethanoic acid has a freezing point of 290 K, causing it to freeze easily in cold climates.
Esterification: The reaction of ethanoic acid with absolute ethanol in the presence of an acid catalyst to produce sweet-smelling esters.
Saponification: The alkaline hydrolysis of esters using sodium hydroxide to regenerate alcohol and form soap salts.
Carbonate Reaction: Ethanoic acid reacts vigorously with carbonates and hydrogencarbonates to release carbon dioxide gas, water, and sodium acetate.

4.5 Soaps and Detergents

Soap Molecules: Sodium or potassium salts of long-chain carboxylic acids.
Hydrophilic End: The ionic head of the soap molecule that interacts strongly with water.
Hydrophobic End: The long hydrocarbon tail of the soap molecule that avoids water and binds to oily dirt.
Micelles: Clusters formed by soap molecules in water, where hydrophobic tails cluster inward around a dirt/oil droplet and hydrophilic heads point outward into the water, forming a stable emulsion.

Scum: Insoluble calcium and magnesium precipitates formed when soap reacts with the minerals present in hard water, reducing cleaning efficiency.
Detergents: Cleansing agents consisting of sodium salts of sulfonic acids or ammonium salts that do not form insoluble precipitates with calcium or magnesium, making them highly effective even in hard water.