Class 12 · Chemistry · English medium · Part 1
Class 12 Chemistry Part 1 companion
An original companion to Chemistry, NCERT Class 12 Chemistry (2026–27 edition). Official textbook ↗ ncert.nic.in
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Chapters
- ENHinglish
Chapter 1: Solutions
Class 12 Chemistry unit 1 studies liquid solutions. - ENHinglish
Chapter 2: Electrochemistry
Electrochemistry links redox reactions and electricity. - ENHinglish
Chapter 3: Chemical Kinetics
Chemical kinetics measures how fast reactions go. - ENHinglish
Chapter 4: The d- and f-Block Elements
The d-block (groups 3–12) fills (n−1)d orbitals; transition elements have an incomplete d subshell in the atom or a common ion (Zn, Cd, Hg excluded). - ENHinglish
Chapter 5: Coordination Compounds
In a coordination compound a metal atom or ion holds a definite set of ligands, ions or molecules that each donate an electron pair.
Also in Hinglish
- Chapter 1: Solutions (Hinglish)
- Chapter 2: Electrochemistry (Hinglish)
- Chapter 3: Chemical Kinetics (Hinglish)
- Chapter 4: d- aur f-Block Elements (Hinglish)
- Chapter 5: Coordination Compounds (Hinglish)
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actinoidऐक्टिनॉयडOne of the fourteen 5f elements, thorium to lawrencium; all are radioactive.Ch 4 · The d- and f-Block Elementsactinoid contractionऐक्टिनॉयड आकुंचनThe decrease in size across the actinoids, larger per element than the lanthanoid contraction.Ch 4 · The d- and f-Block Elementsactivated complexसक्रियित संकुलThe short-lived, highest-energy arrangement of atoms on the way from reactants to products.Ch 3 · Chemical Kineticsactivation energyसक्रियण ऊर्जाThe energy barrier Ea between the reactants and the activated complex: the extra energy colliding molecules need in order to react.Ch 3 · Chemical Kineticsalloyमिश्रातुA metallic blend of a metal with other elements, e.g. brass (Cu–Zn).Ch 4 · The d- and f-Block Elementsambidentate ligandA ligand with two different possible donor atoms that binds through either one, such as NO2- (N or O) or SCN- (S or N).Ch 5 · Coordination Compoundsazeotropeस्थिरक्वाथीA liquid mixture that boils at a constant temperature to give vapour of the same composition, so distillation cannot separate it.Ch 1 · SolutionsC
catalystउत्प्रेरकA substance that speeds up a reaction by opening a path of lower activation energy and is unchanged chemically at the end.Ch 3 · Chemical Kineticscell constantसेल स्थिरांकThe ratio l/A for a conductivity cell, found from G * = R κ with a standard KCl solution.Ch 2 · Electrochemistrycentral atom or ionकेंद्रीय परमाणुThe metal atom or ion at the centre of a coordination entity; it accepts electron pairs from the ligands, so it acts as a Lewis acid.Ch 5 · Coordination CompoundschelateकीलेटA ring formed when one ligand binds the same metal ion through two or more donor atoms; chelate complexes are usually more stable than similar non-chelated ones.Ch 5 · Coordination Compoundschemical kineticsरासायनिक बलगतिकीThe branch of chemistry that studies how fast reactions happen, what controls their speed and the steps by which they occur.Ch 3 · Chemical Kineticscolligative propertyअणुसंख्य गुणधर्मA property of a dilute solution that depends on the number of solute particles, not on what they are.Ch 1 · SolutionsconductivityचालकताThe reciprocal of resistivity, κ = 1/ρ: the conductance of a unit cube of material, in S m⁻¹ or S cm⁻¹.Ch 2 · Electrochemistrycoordination compoundउपसहसंयोजन यौगिकA compound in which a metal atom or ion holds a definite number of neighbouring ions or molecules, each donating an electron pair, such as [Cu(NH3)4]SO4.Ch 5 · Coordination Compoundscoordination entityThe central atom together with the ligands bonded to it, written inside square brackets; it may be a cation, an anion or a neutral molecule.Ch 5 · Coordination Compoundscoordination numberउपसहसंयोजन संख्याThe number of ligand donor atoms joined to the central atom by σ bonds.Ch 5 · Coordination Compoundscoordination polyhedronThe shape traced by the donor atoms around the central atom, for example octahedral, tetrahedral or square planar.Ch 5 · Coordination Compoundscoordination sphereThe central atom and its ligands, enclosed in square brackets; ions written outside the brackets are counter ions.Ch 5 · Coordination Compoundscorrosionसंक्षारणThe slow electrochemical oxidation of a metal surface by its surroundings, such as the rusting of iron.Ch 2 · Electrochemistrycrystal field splittingक्रिस्टल क्षेत्र विपाटनThe energy gap that opens between groups of d orbitals when ligands surround a metal ion; Δ o in an octahedral field and Δ t in a tetrahedral one.Ch 5 · Coordination CompoundsD
d–d transitionThe jump of an electron between the split d-orbital sets of a metal ion on absorbing visible light; the cause of most transition metal colours.Ch 4 · The d- and f-Block Elementsdiamagneticप्रतिचुंबकीयWeakly repelled by a magnetic field; all electrons paired.Ch 4 · The d- and f-Block ElementsdisproportionationअसमानुपातनA reaction in which one species is both oxidised and reduced, e.g. 2Cu+ -> Cu²+ + Cu.Ch 4 · The d- and f-Block ElementsE
effective collisionप्रभावी संघट्टA collision with at least the threshold energy and a suitable orientation, so that it leads to products.Ch 3 · Chemical Kineticselectrode potentialइलेक्ट्रोड विभवThe potential difference between an electrode and the electrolyte around it.Ch 2 · Electrochemistryelectrolytic cellवैद्युत अपघटनी सेलA cell in which an external electrical supply drives a non-spontaneous reaction.Ch 2 · Electrochemistryelementary reactionप्राथमिक अभिक्रियाA reaction that takes place in a single step, exactly as its equation is written.Ch 3 · Chemical Kineticsemf of a cellविद्युत वाहक बलThe potential difference between the electrodes of a cell when no current is drawn.Ch 2 · ElectrochemistryenantiomerOne of a pair of molecules or ions that are mirror images but cannot be superimposed (they are chiral); the two rotate plane-polarised light in opposite directions.Ch 5 · Coordination Compoundsenthalpy of atomisationपरमाणुकरण एन्थैल्पीThe enthalpy change when one mole of an element is converted into separate gaseous atoms.Ch 4 · The d- and f-Block Elementsexchange energyविनिमय ऊर्जाStabilisation gained by electrons with parallel spins in degenerate orbitals, roughly proportional to the number of such pairs.Ch 4 · The d- and f-Block ElementsF
Faraday constantफैराडे स्थिरांकThe charge on one mole of electrons, F = 96 485 C mol⁻¹.Ch 2 · Electrochemistryfuel cellईंधन सेलA galvanic cell whose fuel and oxidant are supplied continuously, such as the hydrogen–oxygen cell.Ch 2 · ElectrochemistryG
galvanic cellगैल्वेनी सेलA cell in which a spontaneous redox reaction drives electrons round an external circuit, so chemical energy becomes electrical work.Ch 2 · ElectrochemistryH
half-lifeअर्धायुHow long a reactant's concentration takes to halve; for a first-order reaction it is 0.693/k.Ch 3 · Chemical KineticsHenry's lawहेनरी का नियमAt constant temperature the partial pressure of a gas over a solution is proportional to its mole fraction in the solution, p = KHx.Ch 1 · Solutionshomoleptic complexA complex with only one kind of ligand, such as [Fe(CO)5]. A heteroleptic complex has two or more kinds.Ch 5 · Coordination CompoundsI
ideal solutionआदर्श विलयनA solution that obeys Raoult's law at every composition, with no heat change and no volume change on mixing.Ch 1 · Solutionsinner orbital complexA complex whose hybrid orbitals use the inner (n-1)d orbitals; for d⁴ – d⁶ ions this forces the d electrons to pair (low spin). An outer orbital complex uses nd orbitals and keeps its electrons unpaired (high spin).Ch 5 · Coordination Compoundsinner transition elementआंतर संक्रमण तत्वAn f-block element, in which the 4f or 5f subshell is being filled.Ch 4 · The d- and f-Block Elementsinterstitial compoundअंतराकाशी यौगिकA compound in which small atoms (H, B, C, N) occupy holes in a metal lattice, e.g. WC.Ch 4 · The d- and f-Block ElementsL
lanthanoidलैन्थेनॉयडOne of the fourteen 4f elements, cerium to lutetium (lanthanum is studied with them).Ch 4 · The d- and f-Block Elementslanthanoid contractionलैन्थेनॉयड आकुंचनThe steady decrease in size from La to Lu, caused by poor shielding by 4f electrons.Ch 4 · The d- and f-Block Elementsligandलिगन्डAn ion or molecule that donates at least one electron pair to the central atom. The number of donor atoms it uses is its denticity.Ch 5 · Coordination Compoundslimiting molar conductivityसीमांत मोलर चालकताThe molar conductivity as the concentration approaches zero, Λ °m.Ch 2 · ElectrochemistryM
molalityमोललताMoles of solute per kilogram of solvent, in mol kg⁻¹ (m); it does not depend on temperature.Ch 1 · Solutionsmolar conductivityमोलर चालकताConductivity divided by molar concentration, Λm = κ/c, in S m² mol⁻¹ or S cm² mol⁻¹.Ch 2 · ElectrochemistrymolarityमोलरताMoles of solute per litre of solution, in mol L⁻¹ (M); it changes slightly with temperature.Ch 1 · Solutionsmole fractionमोल अंशMoles of one component divided by the total moles of all components; the mole fractions of a solution add up to 1.Ch 1 · Solutionsmolecularityआण्विकताThe number of species that must collide at once in an elementary step: one, two or, rarely, three.Ch 3 · Chemical KineticsO
order of a reactionअभिक्रिया की कोटिThe sum of the powers of the concentration terms in the rate law. It is found by experiment and may be zero or a fraction.Ch 3 · Chemical Kineticsosmotic pressureपरासरण दाबThe extra pressure that must be put on a solution to stop solvent flowing into it through a semipermeable membrane; Π = CRT.Ch 1 · SolutionsoverpotentialअधिविभवThe extra voltage, beyond the value from electrode potentials, needed to make a slow electrode reaction run at a useful rate.Ch 2 · ElectrochemistryP
paramagneticअनुचुंबकीयAttracted into a magnetic field because of unpaired electrons.Ch 4 · The d- and f-Block Elementspre-exponential factorआवृत्ति गुणांकThe constant A in k = A e -Ea/RT; it reflects how often reactant molecules collide.Ch 3 · Chemical Kineticspseudo first-order reactionछद्म प्रथम कोटि अभिक्रियाA reaction of higher order that behaves as first order because the other reactants are in large excess.Ch 3 · Chemical KineticsR
Raoult's lawराउल्ट का नियमEvery volatile component of a solution has a partial vapour pressure equal to its mole fraction times its pure vapour pressure, pi = xi pi °.Ch 1 · Solutionsrate constantवेग स्थिरांकThe constant k in a rate law; it is fixed for a reaction at a given temperature and equals the rate at unit concentrations.Ch 3 · Chemical Kineticsrate lawवेग नियमAn experimentally found equation giving the rate in terms of reactant concentrations, such as Rate = k[A] x[B] y.Ch 3 · Chemical Kineticsrate of reactionअभिक्रिया का वेगHow quickly the concentration of a reactant falls or of a product rises, per unit time, divided by that species' coefficient in the balanced equation.Ch 3 · Chemical Kineticsrate-determining stepवेग निर्धारक पदThe slowest step of a mechanism, which limits the rate of the overall reaction.Ch 3 · Chemical KineticsS
salt bridgeलवण सेतुA tube of an inert electrolyte in jelly that joins two half-cells and keeps both solutions electrically neutral.Ch 2 · Electrochemistrysaturated solutionसंतृप्त विलयनA solution in dynamic equilibrium with undissolved solute, so it cannot dissolve any more at that temperature and pressure.Ch 1 · SolutionssolubilityविलेयताThe largest amount of a substance that dissolves in a stated amount of solvent at a given temperature and pressure.Ch 1 · SolutionssoluteविलेयAny component of a solution other than the solvent.Ch 1 · SolutionssolutionविलयनA mixture that is uniform throughout, down to the scale of molecules, made of two or more components.Ch 1 · SolutionssolventविलायकThe component of a solution that is usually present in the largest amount and decides its physical state.Ch 1 · Solutionsspectrochemical seriesLigands listed in order of the splitting they cause, found from the light their complexes absorb: halide ions at the weak end, CN- and CO at the strong end.Ch 5 · Coordination Compoundsspin-only magnetic momentकेवल प्रचक्रण चुंबकीय आघूर्णμ = √ n(n+2) BM, the moment due to the spins of n unpaired electrons alone.Ch 4 · The d- and f-Block Elementsstandard electrode potentialमानक इलेक्ट्रोड विभवThe reduction potential of a half-cell with all species in their standard states, measured against the SHE; symbol E °.Ch 2 · Electrochemistrystandard hydrogen electrodeमानक हाइड्रोजन इलेक्ट्रोडPlatinised platinum in 1 M H+ with hydrogen at 1 bar; its potential is defined as 0 V.Ch 2 · Electrochemistrysynergic bondingTwo-way bonding in metal carbonyls: CO donates a lone pair to the metal (σ) and the metal donates d electrons back into CO's empty π * orbitals (π); each strengthens the other.Ch 5 · Coordination CompoundsT
transition elementसंक्रमण तत्वAn element with an incomplete d subshell in its atom or in a common ion; the d-block minus group 12.Ch 4 · The d- and f-Block ElementsV
van't Hoff factorवान्ट हॉफ गुणकThe ratio i of the particles actually present to the formula units dissolved; above 1 for dissociation, below 1 for association.Ch 1 · Solutionsncert.ai is an independent learning companion aligned to the NCERT curriculum. It is not affiliated with or endorsed by NCERT.