Carbon And its Compounds-C

CloseWhen one hydrogen atom in a hydrocarbon is replaced by another atom or group (e.g., –OH, –Cl), carbon’s valency remains 4 because it still forms four bonds. The atomic mass and structure change, and reactivity often changes dramatically.

CloseCarbon skeletons (straight, branched, or ring) can exist as saturated compounds (only single bonds, e.g., cyclohexane) or unsaturated compounds (double/triple bonds, e.g., cyclohexene). Chain arrangement does not determine saturation.

CloseHydrocarbons (compounds of only C and H) exhibit structural diversity: straight chains (n-butane), branched chains (isobutane), and rings (cyclohexane, benzene). This is due to carbon’s catenation ability.

CloseEthane (C₂H₆) has the structure H₃C–CH₃. Each carbon atom is bonded to three hydrogen atoms and one carbon atom, satisfying carbon’s tetravalency (4 bonds).

CloseIntroducing heteroatoms (O, N, halogens) into carbon compounds creates functional groups (–OH, –NH₂, –Cl, etc.) that impart specific chemical properties and reactivity, different from the parent hydrocarbon.

CloseTetravalency (ability to form four bonds) allows carbon to bond with many elements, while catenation (self-linking) allows formation of long chains, branches, and rings. Together, these create millions of compounds.

CloseAbundance alone is not enough (silicon is also abundant). Carbon’s unique ability to form stable, long chains and rings via strong C–C covalent bonds is the real reason for the vast number of carbon compounds.

CloseEthyne (acetylene) is an alkyne with a triple bond between two carbons. Each carbon is bonded to one hydrogen. C₂H₄ is ethene, C₂H₆ is ethane, CH₄ is methane.

Closen-Butane (straight chain) and isobutane (branched chain) have the same molecular formula C₄H₁₀ but different structural arrangements of atoms. This is structural isomerism, not allotropy or isotopes.

CloseThe carbon-carbon single bond has a bond energy of approximately 348 kJ/mol. This high strength, along with carbon’s small size, allows stable long-chain molecules that do not easily break apart.

CloseTraditionally, organic chemistry excludes carbonates (CO₃²⁻), bicarbonates (HCO₃⁻), and oxides of carbon (CO, CO₂) because these are simple ionic or covalent molecules better classified as inorganic compounds.

CloseButane (C₄H₁₀) has two structural isomers: n-butane (straight chain) and isobutane (2-methylpropane, branched chain). No other structural isomers exist for C₄H₁₀.

CloseAlkanes have the general formula CₙH₂ₙ₊₂ and contain only single covalent bonds (saturated). Alkenes have double bonds, alkynes have triple bonds, and arenes are aromatic hydrocarbons.

CloseTetravalency allows carbon to form four bonds with various elements; catenation allows it to form stable bonds with itself, creating chains and rings. No other element combines these two properties so effectively.

CloseUnsaturated compounds contain at least one multiple bond (C=C or C≡C). They can add more atoms (e.g., hydrogen) across the multiple bond, unlike saturated compounds (only single bonds).

CloseBefore 1828, the “vital force theory” held that organic compounds could only be synthesized by living organisms using a special “vital force,” and could not be made artificially.

CloseIn 1828, Wohler heated ammonium cyanate (NH₄CNO), an inorganic salt, and obtained urea (NH₂–CO–NH₂), an organic compound. This disproved the vital force theory.

CloseSaturated compounds (alkanes) have no double or triple bonds; every carbon atom forms four single bonds, maximizing the number of hydrogen atoms (CₙH₂ₙ₊₂). They are “saturated” with hydrogen.

CloseAlkenes contain at least one carbon-carbon double bond (C=C) and have the general formula CₙH₂ₙ. Examples: ethene (C₂H₄), propene (C₃H₆). Alkynes have triple bonds; alkanes have single bonds.

CloseCarbon’s small atomic radius means its 6 protons strongly attract the shared electron pairs in covalent bonds. The small size increases electron density between nuclei, making bonds short and strong.

CloseCyclohexane is a saturated cyclic hydrocarbon (cycloalkane) with 6 carbon atoms in a ring. Each carbon is bonded to two hydrogens (and two carbons), giving formula C₆H₁₂. C₆H₆ is benzene (aromatic).

CloseEthyne (C₂H₂, acetylene) has a triple bond (one sigma + two pi bonds) between the two carbon atoms, sharing three pairs of electrons (six electrons total). No carbon-carbon bond can have more than three bonds.

CloseAlkanes are saturated hydrocarbons with only C–C and C–H single bonds. Alkenes contain at least one C=C double bond, making them unsaturated and more reactive than alkanes.

CloseCarbon bonds readily with H, O, N, S, halogens, and metals, forming millions of compounds. This “friendliness” (versatility) is due to its tetravalency and moderate electronegativity.

CloseButane is an alkane with 4 carbon atoms. Using the alkane formula CₙH₂ₙ₊₂, with n=4, we get C₄H₁₀. C₃H₈ is propane, C₂H₆ is ethane, C₅H₁₂ is pentane.

CloseEthane (C₂H₆) is an alkane with two carbon atoms joined by a single bond, each carbon bonded to three hydrogens. CH₄ = methane, C₂H₄ = ethene, C₂H₂ = ethyne.

CloseThe carbon skeleton (or backbone) is the chain, branched, or ring arrangement of carbon atoms in an organic molecule. Hydrogen atoms are attached to this skeleton but are not part of the skeleton itself.

CloseIn 1828, Friedrich Wohler synthesized urea (an organic compound) from ammonium cyanate (an inorganic compound), showing that no “vital force” was needed to make organic compounds.

CloseStructural isomers share the same molecular formula but differ in the bonding arrangement of atoms (e.g., n-butane and isobutane, both C₄H₁₀). Allotropes differ in physical form of the same element.

CloseThe first step is to arrange the carbon skeleton (determine how carbon atoms are connected—straight, branched, or ring). Then, add hydrogen atoms to satisfy carbon’s tetravalency, followed by other atoms.

CloseEthene (ethylene) is an alkene with a double bond between two carbons (C=C). Each carbon is bonded to two hydrogens. C₂H₂ is ethyne (triple bond), C₂H₆ is ethane (single bond).

CloseCarbon chains can range from 1 carbon (methane) to hundreds or even thousands of carbons (e.g., polyethylene, waxes, biological macromolecules). No restriction on chain length exists.

CloseThe vital force theory (early 19th century) claimed that organic compounds could only be produced by living organisms using a mysterious “vital force.” Wohler’s urea synthesis disproved this.

CloseButane (C₄H₁₀) exists as two structural isomers: n-butane (straight chain) and isobutane (2-methylpropane, branched). The molecular formula is identical, but the arrangement of atoms differs.

CloseLarger atoms have valence electrons farther from the nucleus, with more shielding by inner electrons. The nucleus attracts shared electron pairs less strongly, resulting in weaker covalent bonds (e.g., Si–Si weaker than C–C).

CloseThe pi bonds in double/triple bonds are weaker and more exposed than sigma bonds, making unsaturated compounds prone to addition reactions (e.g., hydrogenation, halogenation). Saturated alkanes are relatively unreactive.

CloseStrong C–C and C–H bonds (348–435 kJ/mol) provide the stability needed for millions of different molecular structures to exist without decomposing. Weak bonds would cause rapid breakdown.

CloseMethane = CH₄ (1 C), ethane = C₂H₆ (2 C), propane = C₃H₈ (3 C). They form the first three members of the alkane homologous series (CₙH₂ₙ₊₂).

CloseCarbon’s small size (atomic radius ~70 pm) allows its nucleus to strongly attract shared electron pairs, creating short, strong bonds. Large atoms form weaker bonds (e.g., lead–lead bonds are very weak).

CloseEthene (C₂H₄) has a carbon-carbon double bond (C=C)—one sigma bond and one pi bond. This distinguishes it from ethane (single) and ethyne (triple).

CloseAlkynes contain at least one carbon-carbon triple bond (C≡C) and have the general formula CₙH₂ₙ₋₂. Examples: ethyne (C₂H₂), propyne (C₃H₄). Alkenes have double bonds; alkanes are saturated.

CloseSaturated compounds (alkanes) have only strong sigma bonds, no pi bonds, and no electron-deficient sites. They undergo substitution reactions (with difficulty) but not addition, making them relatively inert.

CloseCyclohexane (C₆H₁₂) is a cyclic (ring) hydrocarbon where six carbon atoms form a closed loop. The “cyclo” prefix indicates a ring structure, not straight or branched.

CloseEthane (C₂H₆) has a carbon-carbon single covalent bond (C–C). Each carbon uses one of its four valence electrons to bond to the other carbon, and the remaining three bond to hydrogens.

CloseHydrocarbons are binary compounds composed exclusively of carbon and hydrogen. Examples: methane (CH₄), ethene (C₂H₄), benzene (C₆H₆). Adding oxygen or other elements gives functionalized derivatives.

CloseBenzene is an aromatic hydrocarbon with 6 carbon atoms and 6 hydrogen atoms, arranged in a ring with alternating double and single bonds (delocalized pi electrons). C₆H₁₂ is cyclohexane (saturated).

CloseNeon is a noble gas with a completely filled outer shell (2,8). It is chemically inert and does not form bonds with any element, including carbon. Carbon readily forms compounds with O, S, and N.

CloseHydrogen atoms in hydrocarbons can be substituted by atoms or groups (e.g., –Cl, –OH, –NH₂) that have a valency of 1, so carbon’s tetravalency remains satisfied. Noble gases do not bond; metals generally form ionic compounds.

CloseAlkenes (C=C) and alkynes (C≡C) are unsaturated because they contain multiple bonds and can add more hydrogen or other atoms. Saturated hydrocarbons (alkanes) have only single bonds.

CloseIn 1828, Friedrich Wohler synthesized urea by heating ammonium cyanate. This landmark year marked the birth of synthetic organic chemistry and the death of the vital force theory.