Class 11 · Chemistry · English medium · Part 1
Class 11 Chemistry Part 1 companion
An interactive companion to Class 11 Chemistry Part 1: original explanations, models, worked problems and practice for moles, atoms, the periodic table, bonding, thermodynamics and equilibrium.
An original companion to Chemistry, NCERT Class 11 Chemistry (2026–27 edition). Official textbook ↗ ncert.nic.in
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Chapters
- ENHinglish
Chapter 1: Some Basic Concepts of Chemistry
Class 11 Chemistry unit 1 lays the foundation for quantitative chemistry. - ENHinglish
Chapter 2: Structure of Atom
Discharge-tube experiments found electrons, protons and neutrons; alpha-particle scattering replaced Thomson's model with Rutherford's nucle - ENHinglish
Chapter 3: Classification of Elements and Periodicity in Properties (Periodic Classification)
Class 11 chemistry: how elements came to be classified (Döbereiner's triads, de Chancourtois, Newlands' octaves, Lothar Meyer, Mendeleev's p - ENHinglish
Chapter 4: Chemical Bonding and Molecular Structure
Why atoms combine and what shapes molecules take. - ENHinglish
Chapter 5: Thermodynamics
Thermodynamics tracks energy changes in bulk matter between equilibrium states. - ENHinglish
Chapter 6: Equilibrium
Equilibrium is dynamic: opposing processes run at equal rates in a closed system.
Also in Hinglish
- Chapter 1: Chemistry ki Kuch Basic Concepts (Hinglish)
- Chapter 2: Atom ki Structure (Hinglish)
- Chapter 3: Elements ka Classification aur Properties mein Periodicity (Hinglish)
- Chapter 4: Chemical Bonding aur Molecular Structure (Hinglish)
- Chapter 5: Thermodynamics (Hinglish)
- Chapter 6: Equilibrium (Hinglish)
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accuracyयथार्थताHow close a result is to the true value.Ch 1 · Some Basic Concepts of Chemistryadiabaticरुद्धोष्मDescribes a wall or process through which no heat passes between system and surroundings.Ch 5 · Thermodynamicsamphoteric oxideउभयधर्मी ऑक्साइडAn oxide that reacts with both acids and bases, such as Al2O3.Ch 3 · Classification of Elements and Periodicity in Propertiesatomic mass unitपरमाणु द्रव्यमान मात्रकA twelfth of a carbon-12 atom's mass, 1.6605×10⁻²⁴ g; symbol u.Ch 1 · Some Basic Concepts of Chemistryatomic numberपरमाणु क्रमांकThe number of protons in the nucleus, Z.Ch 2 · Structure of Atomatomic orbitalकक्षकA one-electron wave function ψ; | ψ |² gives the probability density.Ch 2 · Structure of Atomatomic radiusपरमाणु त्रिज्याHalf the distance between the nuclei of two bonded identical atoms: the covalent radius for non-metals, the metallic radius for metals.Ch 3 · Classification of Elements and Periodicity in PropertiesB
bond enthalpyआबंध एन्थैल्पीThe energy needed to break one mole of a given type of bond, with all species in the gas phase.Ch 4 · Chemical Bonding and Molecular Structurebond enthalpyआबंध एन्थैल्पीThe enthalpy needed to break one mole of a given bond in gaseous molecules; usually a mean over similar bonds.Ch 5 · Thermodynamicsbond orderआबंध कोटिThe number of bonds between two atoms: shared pairs in a Lewis structure, or 1 2 (Nb - Na) in MO theory.Ch 4 · Chemical Bonding and Molecular Structurebuffer solutionबफर विलयनA weak acid with its conjugate base, or a weak base with its conjugate acid, that resists pH change.Ch 6 · EquilibriumC
common ion effectसम-आयन प्रभावSuppression of an ionization or solubility by adding an ion already in the equilibrium.Ch 6 · EquilibriumcompoundयौगिकA pure substance of two or more elements combined chemically in a fixed ratio by mass.Ch 1 · Some Basic Concepts of Chemistryconjugate acid–base pairसंयुग्मी अम्ल-क्षारक युग्मAn acid and a base that differ by one proton.Ch 6 · Equilibriumcovalent bondसहसंयोजी आबंधA bond formed when two atoms share one or more pairs of electrons.Ch 4 · Chemical Bonding and Molecular StructureD
de Broglie wavelengthदे ब्रॉग्ली तरंगदैर्ध्यThe wavelength λ = h/mv of a moving particle.Ch 2 · Structure of Atomdegenerate orbitalsअपभ्रष्ट कक्षकOrbitals of equal energy, such as the three 2p orbitals.Ch 2 · Structure of Atomdegree of ionizationआयनन की मात्राThe fraction α of a weak electrolyte that is ionized.Ch 6 · Equilibriumdiagonal relationshipविकर्ण संबंधThe resemblance between a second-period element and the element one place down and to the right, such as Li and Mg.Ch 3 · Classification of Elements and Periodicity in Propertiesdipole momentद्विध्रुव आघूर्णCharge × separation of the centres of positive and negative charge, μ = Q × r, usually in debye (D).Ch 4 · Chemical Bonding and Molecular Structuredynamic equilibriumगतिक साम्यA state of a closed system in which opposing processes run at equal rates, so no measurable property changes.Ch 6 · EquilibriumE
effective nuclear chargeप्रभावी नाभिकीय आवेशThe net nuclear charge an electron feels after shielding.Ch 2 · Structure of Atomeffective nuclear chargeप्रभावी नाभिकीय आवेशThe net positive charge an outer electron feels after inner electrons screen part of the nuclear charge.Ch 3 · Classification of Elements and Periodicity in Propertieselectrolyteविद्युत्-अपघट्यA substance whose aqueous solution conducts because it contains ions.Ch 6 · Equilibriumelectron gain enthalpyइलेक्ट्रॉन लब्धि एन्थैल्पीThe enthalpy change when an isolated gaseous atom gains an electron; negative when energy is released.Ch 3 · Classification of Elements and Periodicity in Propertieselectronegativityविद्युत्-ऋणात्मकताThe relative ability of an atom in a molecule to pull a shared electron pair towards itself.Ch 3 · Classification of Elements and Periodicity in Propertieselectronic configurationइलेक्ट्रॉनिक विन्यासHow an atom's electrons are distributed among its orbitals.Ch 2 · Structure of Atomelementतत्वA pure substance made of only one kind of atom.Ch 1 · Some Basic Concepts of Chemistryempirical formulaमूलानुपाती सूत्रThe simplest whole-number ratio of the atoms in a compound.Ch 1 · Some Basic Concepts of Chemistryenthalpyएन्थैल्पीH = U + pV; its change equals the heat absorbed at constant pressure.Ch 5 · Thermodynamicsentropyएन्ट्रॉपीA state function, S, measuring how widely matter and energy are spread out; it rises in every spontaneous change.Ch 5 · Thermodynamicsequilibrium constantसाम्य स्थिरांकThe value, fixed at a given temperature, of products over reactants with each concentration (or pressure) raised to its coefficient.Ch 6 · Equilibriumextensive propertyविस्तीर्ण गुणधर्मA property proportional to the amount of matter, such as mass, volume or enthalpy.Ch 5 · ThermodynamicsF
formal chargeऔपचारिक आवेशValence electrons of the free atom minus its lone-pair electrons minus half its bonding electrons in a Lewis structure.Ch 4 · Chemical Bonding and Molecular StructureG
Gibbs energyगिब्ज़ ऊर्जाG = H - TS; a process at constant T and p is spontaneous when Δ G < 0.Ch 5 · Thermodynamicsgroupवर्गA vertical column (1 to 18) of elements with similar outer electronic configurations and similar chemistry.Ch 3 · Classification of Elements and Periodicity in PropertiesH
Hess's lawहेस का नियमA reaction enthalpy is the same whether the reaction happens in one step or several, so step enthalpies add.Ch 5 · Thermodynamicsheterogeneous equilibriumविषमांगी साम्यAn equilibrium involving more than one phase.Ch 6 · EquilibriumhybridisationसंकरणMixing of atomic orbitals of similar energy on one atom to give an equal number of equivalent hybrid orbitals.Ch 4 · Chemical Bonding and Molecular Structurehydrogen bondहाइड्रोजन आबंधThe attraction between H bonded to F, O or N and a lone pair on another F, O or N atom.Ch 4 · Chemical Bonding and Molecular Structurehydrolysis of saltsलवणों का जल-अपघटनReaction of a salt’s ions with water that makes the solution acidic or basic.Ch 6 · EquilibriumI
intensive propertyगहन गुणधर्मA property independent of the amount of matter, such as temperature, pressure or density.Ch 5 · Thermodynamicsinternal energyआंतरिक ऊर्जाThe total energy stored in a system; only its change, Δ U, can be measured.Ch 5 · Thermodynamicsionic (electrovalent) bondआयनिक आबंधThe electrostatic attraction between oppositely charged ions formed by transfer of electrons.Ch 4 · Chemical Bonding and Molecular Structureionic product of waterजल का आयनिक गुणनफलKw = [H+][OH-], 10⁻¹⁴ at 298 K.Ch 6 · Equilibriumionization enthalpyआयनन एन्थैल्पीThe energy needed to remove the most loosely held electron from an isolated gaseous atom (or ion) in its ground state, in kJ mol⁻¹.Ch 3 · Classification of Elements and Periodicity in PropertiesisobarसमभारिकAtoms of different elements that have the same mass number.Ch 2 · Structure of Atomisoelectronic speciesसमइलेक्ट्रॉनी स्पीशीज़Atoms or ions that have the same number of electrons, such as Cl-, Ar and K+.Ch 3 · Classification of Elements and Periodicity in Propertiesisotopeसमस्थानिकAtoms of one element with different numbers of neutrons.Ch 2 · Structure of AtomL
lattice enthalpyजालक एन्थैल्पीThe energy needed to separate one mole of an ionic solid completely into gaseous ions.Ch 4 · Chemical Bonding and Molecular Structurelattice enthalpyजालक एन्थैल्पीThe enthalpy change when 1 mol of an ionic solid separates into its gaseous ions.Ch 5 · ThermodynamicsLe Chatelier’s principleला-शातलिए सिद्धांतAn equilibrium disturbed by a change of concentration, pressure or temperature shifts so as to partly undo the change.Ch 6 · EquilibriumLewis acidलूइस अम्लAn electron-pair acceptor; a Lewis base is a donor.Ch 6 · EquilibriumLewis symbolलूइस प्रतीकAn element's symbol surrounded by one dot for each valence electron.Ch 4 · Chemical Bonding and Molecular Structurelimiting reagentसीमांत अभिकर्मकThe reactant used up first, which limits the amount of product.Ch 1 · Some Basic Concepts of Chemistryline spectrumरेखा स्पेक्ट्रमA spectrum of sharp lines at wavelengths typical of an element.Ch 2 · Structure of AtomM
metalloidउपधातुAn element with properties between those of metals and non-metals, such as silicon and arsenic.Ch 3 · Classification of Elements and Periodicity in Propertiesmixtureमिश्रणTwo or more pure substances mixed in any ratio; separable by physical methods.Ch 1 · Some Basic Concepts of ChemistrymolalityमोललताMoles of solute per kilogram of solvent (m); it does not change with temperature.Ch 1 · Some Basic Concepts of Chemistrymolar massमोलर द्रव्यमानHow many grams one mole of a substance weighs; unit g mol⁻¹.Ch 1 · Some Basic Concepts of ChemistrymolarityमोलरताMoles of solute per litre of solution (M); it changes with temperature.Ch 1 · Some Basic Concepts of ChemistrymoleमोलThe SI unit of amount of substance: exactly 6.02214076×10²³ entities.Ch 1 · Some Basic Concepts of Chemistrymole fractionमोल अंशThe moles of one component divided by the total moles in the mixture.Ch 1 · Some Basic Concepts of Chemistrymolecular orbitalआण्विक कक्षकAn orbital that spreads over the whole molecule, formed by combining atomic orbitals; it can be bonding or antibonding.Ch 4 · Chemical Bonding and Molecular StructureN
nodeनोडA surface of zero probability density: radial (sphere) or angular (plane or cone).Ch 2 · Structure of AtomO
octet ruleअष्टक नियमAtoms tend to lose, gain or share electrons until they have eight in their valence shell (two for hydrogen).Ch 4 · Chemical Bonding and Molecular Structureoxidation stateऑक्सीकरण अवस्थाThe charge an atom would carry if every shared pair were given to the more electronegative partner.Ch 3 · Classification of Elements and Periodicity in PropertiesP
periodआवर्तA horizontal row of the periodic table; its number is the principal quantum number of the valence shell.Ch 3 · Classification of Elements and Periodicity in Propertiesperiodic lawआवर्त नियमThe properties of elements repeat at regular intervals when the elements are arranged by atomic number (Mendeleev used atomic mass).Ch 3 · Classification of Elements and Periodicity in PropertiespHThe negative base-10 logarithm of the hydrogen ion activity, about - log [H+].Ch 6 · EquilibriumphotonफोटॉनA packet (quantum) of electromagnetic energy, E = h ν.Ch 2 · Structure of Atompi (π) bondपाई आबंधA bond formed by sideways overlap of parallel p orbitals, with electron density above and below the bond axis.Ch 4 · Chemical Bonding and Molecular Structureprecisionपरिशुद्धताHow closely repeated measurements agree with each other.Ch 1 · Some Basic Concepts of ChemistryQ
quantum numbersक्वांटम संख्याएँn, l, ml and ms, which label an orbital and an electron's spin.Ch 2 · Structure of AtomR
reaction quotientअभिक्रिया भागफलThe K expression evaluated at any moment; comparing Q with K gives the direction of net reaction.Ch 6 · Equilibriumrepresentative elementप्रतिनिधि तत्वAn s- or p-block element (groups 1, 2 and 13 to 18), also called a main group element.Ch 3 · Classification of Elements and Periodicity in Propertiesresonance hybridअनुनाद संकरThe one real structure of a species that needs two or more canonical Lewis structures to describe it.Ch 4 · Chemical Bonding and Molecular Structurereversible processउत्क्रमणीय प्रक्रमA process run through near-equilibrium states, so that an infinitesimal change could reverse it at any stage.Ch 5 · ThermodynamicsS
sigma (σ) bondसिग्मा आबंधA bond formed by head-on overlap of orbitals along the line joining the two nuclei.Ch 4 · Chemical Bonding and Molecular Structuresignificant figuresसार्थक अंकThe certain digits of a measurement plus one estimated digit.Ch 1 · Some Basic Concepts of Chemistrysolubility product constantविलेयता गुणनफलThe equilibrium constant Ksp between a sparingly soluble salt and its ions.Ch 6 · Equilibriumspontaneous processस्वतः प्रवर्तित प्रक्रमA process that can proceed by itself without continuing outside help, however slowly.Ch 5 · Thermodynamicsstandard enthalpy of formationमानक संभवन एन्थैल्पीThe enthalpy change when 1 mol of a compound forms from its elements, all in their standard or reference states.Ch 5 · Thermodynamicsstate functionअवस्था फलनA property that depends only on the present state, so its change depends only on the initial and final states.Ch 5 · Thermodynamicsstationary stateस्थिर अवस्थाIn Bohr's model, an allowed orbit of fixed energy.Ch 2 · Structure of AtomstoichiometryरससमीकरणमितिCalculating amounts of reactants and products from a balanced equation.Ch 1 · Some Basic Concepts of ChemistrysystemनिकायThe part of the universe chosen for study; everything else that can interact with it is the surroundings.Ch 5 · ThermodynamicsT
transition elementसंक्रमण तत्वA d-block element (groups 3 to 12) in which electrons enter the inner (n − 1)d subshell.Ch 3 · Classification of Elements and Periodicity in PropertiesU
uncertainty principleअनिश्चितता सिद्धांतPosition and momentum cannot both be known exactly: Δ x Δ px ≥ h/4 π.Ch 2 · Structure of AtomW
work functionकार्यफलनThe minimum energy, h ν0, that frees an electron from a metal.Ch 2 · Structure of Atomncert.ai is an independent learning companion aligned to the NCERT curriculum. It is not affiliated with or endorsed by NCERT.