Q.Give hybridisation of carbon in
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Carbon's strong catenation and unique π-bonding ability let it exist in several structurally distinct allotropes. Diamond is a rigid, three-dimensional covalent network in which every carbon is sp3 hybridised and tetrahedrally bonded to four neighbours (C–C = 154 pm); this extended, strongly-directional bonding with no weak points anywhere makes diamond the hardest known natural substance with an extremely high melting point, but also an electrical insulator, since all four valence electrons of every carbon are locked into localised σ bonds. Graphite, by contrast, is built from flat hexagonal sheets of sp2-hybridised carbon (in-layer C–C = 141.5 pm), each carbon using three electrons for in-plane σ bonds and delocalising its fourth electron into a mobile π system spanning the whole sheet — this delocalisation makes graphite an electrical conductor along the layers, while the weak van der Waals forces between the widely-separated layers (340 pm apart) let the sheets slide past each other, making graphite soft and useful as a solid lubricant. This single structural contrast — rigid 3-D sp3 network versus slippery layered sp2 sheets — explains essentially all the differing physical properties of the two allotropes. Fullerenes are a third, molecular form: closed, cage-like spheres (the famous $C_ …
A carbon atom's hybridisation is fixed by how many sigma-bonded neighbours (and lone pairs) surround it, and this differs across these four carbon-containing species. …
Carbon's hybridisation is determined by the number of sigma-bonded/lone-pair centres around it: 4 gives sp3 (tetrahedral), 3 gives sp2 (planar/trigonal).
(a) CO32− (carbonate ion): the central carbon is bonded to 3 oxygen atoms with no lone pair on carbon, and the ion is trigonal planar with delocalized π bonding (resonance) across all 3 C-O bonds. Carbon is sp2 hybridized (three sp2 orbitals form 3 σ bonds to O; the unhybridized 2p orbital takes part in delocalized π bonding).
(b) Diamond: each carbon atom is bonded to 4 other carbon atoms by single covalent bonds in a rigid three-dimensional tetrahedral network. Carbon is sp3 hybridized, which explains diamond's tetrahedral bond angles (109.5°) and extreme hardness.
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- CBSE 2025Set ANNUAL1 markMCQQ.Thermodynamically the most stable form of carbon is(a) Diamond(b) Graphite(c) Peat(d) Coal
›Reveal solutionSolution
Graphite is the thermodynamically most stable form of carbon under normal conditions.
Among carbon's allotropes/forms, graphite has the lowest standard Gibbs free energy (and lowest enthalpy) at room temperature and pressure, making it the thermodynamically most stable form — this is why diamond is described as being 'metastable' (kinetically stable but thermodynamically less stable than graphite, converting to graphite only under extreme c …
- CBSE 2024Set ANNUAL1 markMCQQ.Which of the following is not sp2 hybridised ?(a) Fullerene(b) Graphite(c) Dry ice(d) Graphene
›Reveal solutionSolution
Fullerene, graphite, and graphene share the same trigonal-planar, sp² carbon bonding of fused six-membered (and, in fullerene, also five-membered) rings; dry ice is solid CO2, whose carbon is sp hybridised in a linear molecule, so it is the odd one out.
Graphite consists of 2-D sheets of sp² carbon atoms, each bonded to three neighbours in a hexagonal honeycomb lattice, with a delocalised pi-electron system above and below each sheet. Graphene is simply a single isolated layer of graphite — chemically identical sp² bonding. Fullerene (C60 etc.) is a closed, curved cage built from the same three-sigma-bonds-per-carbon sp² framework, just curved by incorporating some five-membered rings among the hexagons. Dry ice, by contrast, is the solid form of carbon dioxide, CO2, a small linear triatomic molecule (O=C=O) in which the central carb …
- CBSE 2024Set ANNUAL1 markMCQQ.The nature of bond in diamond is(a) Ionic(b) Covalent(c) Co-ordinate covalent(d) Metallic
›Reveal solutionSolution
Diamond is a giant covalent (network) solid, held together entirely by C–C covalent bonds.
In diamond, every carbon atom is sp³ hybridized and forms four strong covalent bonds to four neighbouring carbon atoms in a tetrahedral arrangement, extending throughout the crystal as a three-dimensional network. This is why diamond is extremely hard …
- CBSE 2023Set ANNUAL1 markMCQQ.Carbon atoms in Fullerene with formula C60 have ________ hybridisation.(a) sp2(b) sp3(c) sp3d(d) sp
›Reveal solutionSolution
Each carbon in C60 fullerene is bonded to exactly three other carbons (forming the closed, ball-shaped network of fused hexagons and pentagons), the same three-connected bonding pattern as planar graphite, so each carbon is sp2 hybridised.
Fullerene C60 consists of 60 carbon atoms arranged in a closed, roughly spherical (football/soccer-ball-shaped) cage made of 20 six-membered rings and 12 five-membered rings. Each carbon atom forms exactly three sigma bonds to three neighbouring carbon atoms (as in graphite's 2-D sheets), leaving one unhybridised p-orbital per carbon that contributes to a delocalised pi system over the cage surface. Three …
- CBSE 2022Set ANNUAL1 markQ.Write / draw the structure of graphite.
›Reveal solutionSolution
Graphite's structure is stacked, planar sheets of hexagonally-arranged, sp2-hybridised carbon atoms.
In graphite, every carbon atom is sp2 hybridised and forms three strong sigma covalent bonds to three neighbouring carbon atoms (C-C bond length about 141.5 pm), building a continuous, flat, honeycomb-like network of fused hexagonal rings - essentially an infinite sheet, similar to a single layer of what is now called graphene. Each carbon atom's fourth (unhybridised) electron sits in a p-orbital perpendicular to the sheet; these p-orbitals overlap to give a delocalised pi-electron cloud spread over the whole sheet, which is why graphite conducts electricity along the plane of the layers.
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- CBSE 2022Set ANNUAL1 markMCQQ.Graphite is(a) A molecular solid(b) A covalent solid(c) A metallic solid(d) Ammorphous (amorphous) solid
›Reveal solutionSolution
Graphite is a giant covalent (network) solid — option (b).
From NCERT Class 11 Chemistry (p-Block, carbon allotropes): in graphite each carbon is sp² hybridised and covalently bonded to three neighbours, forming hexagonal sheets; the whole layer is one giant covalent network. The fourth electron is delocalised over the layer (giving electr …
- CBSE 2022Set ANNUAL1 markMCQQ.In graphite, electrons are(a) Localised on every third carbon(b) Present in anti bonding orbital(c) Localised on each carbon(d) Spread out between the structures
›Reveal solutionSolution
Graphite's electrons are delocalised/spread out across the layers — option (d).
From NCERT Class 11 Chemistry (p-Block, carbon allotropes): in graphite each carbon is sp² hybridised, forming three σ-bonds within a planar hexagonal sheet. The remaining unhybridised p-electron on every carbon forms a delocalised π-system spread over the entire layer. These mobile, delocalised electrons …
- CBSE 2019Set ANNUAL1 markQ.Fill in the blank: Lamp black is an ______ allotrope of carbon.
›Reveal solutionSolution
Carbon exists in crystalline forms (diamond, graphite) and amorphous forms (lamp black, coke, charcoal) that lack a regular repeating lattice.
Carbon's allotropes are broadly divided into crystalline allotropes, where atoms are arranged in a well-defined repeating three-dimensional lattice (diamond: tetrahedral sp3 network; graphite: layered sp2 sheets), and amorphous allotropes, which consist of very fine crystallites of graphite arranged without long-range order. Lamp bl …
- CBSE 2018Set ANN1 markQ.The allotrope of carbon with the highest thermodynamic stability is _________.
›Reveal solutionSolution
Graphite is the thermodynamically most stable allotrope of carbon at room temperature and pressure.
Carbon exists as diamond, graphite, fullerenes, etc. At ordinary temperature and pressure, graphite has the lowest free energy, so it is the reference (most stable) allotrope; diamond is only metastable and very slowly conver …
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