In short: Class 11 Chemistry spans three branches - Physical, Inorganic, and Organic. This formula sheet covers all key equations, relationships, and rules from every chapter, sorted by branch so you can revise efficiently. Whether it is the mole concept, periodic trends, or organic nomenclature, everything is here in one place.
How This Formula Sheet Is Organised
Chemistry is not like Physics or Maths where every chapter produces neat equations. In Chemistry, "formulas" include mathematical equations (Physical Chemistry), periodic trends and rules (Inorganic), and naming conventions plus molecular formulas (Organic).
This sheet is divided into three sections matching the three branches. Within each branch, formulas are listed chapter-wise following the CBSE 2026-27 syllabus.
Part 1 - Physical Chemistry
Physical Chemistry is the most formula-heavy branch. These chapters involve calculations, so you need to know the equations and their units.
Chapter 1 - Some Basic Concepts of Chemistry
| Formula | Expression | Unit |
|---|---|---|
| Mole concept | n = Given mass / Molar mass | mol |
| Number of particles | N = n x N(A), where N(A) = 6.022 x 10^23 | - |
| Molar mass | Mass of 1 mole of substance | g/mol |
| Molarity | M = Moles of solute / Volume of solution in litres | mol/L |
| Molality | m = Moles of solute / Mass of solvent in kg | mol/kg |
| Mass percentage | (Mass of solute / Mass of solution) x 100 | % |
| Mole fraction | x(A) = n(A) / (n(A) + n(B)) | Dimensionless |
| Empirical formula mass | Sum of atomic masses in simplest ratio | g/mol |
| Gay-Lussac's law | Volumes of reacting gases are in simple whole number ratios | - |
Chapter 2 - Structure of Atom
| Formula | Expression | Unit |
|---|---|---|
| de Broglie wavelength | lambda = h / (mv) | m |
| Energy of photon | E = h f = hc / lambda | J |
| Bohr radius | r(n) = 0.529 x n^2 / Z angstrom | angstrom |
| Energy of nth orbit | E(n) = -13.6 Z^2 / n^2 eV | eV |
| Velocity in nth orbit | v(n) = 2.18 x 10^6 x Z / n m/s | m/s |
| Heisenberg uncertainty | Delta(x) x Delta(p) >= h / (4 pi) | J s |
| Rydberg formula | 1/lambda = R(H) (1/n1^2 - 1/n2^2) | m^-1 |
| Photoelectric equation | KE(max) = h f - phi (work function) | J |
Chapter 3 - States of Matter
| Formula | Expression | Unit |
|---|---|---|
| Ideal gas equation | PV = nRT | Pa m^3 |
| Boyle's law | P1 V1 = P2 V2 (constant T, n) | - |
| Charles's law | V1/T1 = V2/T2 (constant P, n) | - |
| Dalton's law | P(total) = p1 + p2 + p3 + ... | Pa |
| Graham's law of diffusion | r1/r2 = sqrt(M2/M1) | - |
| van der Waals equation | (P + an^2/V^2)(V - nb) = nRT | Pa m^3 |
| Compressibility factor | Z = PV / (nRT) | Dimensionless |
| RMS speed | u(rms) = sqrt(3RT/M) | m/s |
| Kinetic energy per mole | KE = (3/2) RT | J/mol |
Chapter 5 - Thermodynamics
| Formula | Expression | Unit |
|---|---|---|
| First law | Delta U = q + w | J |
| Work (expansion) | w = -P(ext) Delta V | J |
| Enthalpy | H = U + PV | J |
| At constant pressure | Delta H = q(p) | J |
| At constant volume | Delta U = q(v) | J |
| Relation | Delta H = Delta U + Delta(n)RT | J |
| Hess's law | Delta H(rxn) = Sum of Delta H(f, products) - Sum of Delta H(f, reactants) | J |
| Kirchhoff's equation | Delta H(T2) = Delta H(T1) + Delta Cp (T2 - T1) | J |
| Gibbs free energy | Delta G = Delta H - T Delta S | J |
| Spontaneity | Delta G < 0 means spontaneous | - |
Chapter 6 - Equilibrium
| Formula | Expression | Unit |
|---|---|---|
| Equilibrium constant (Kc) | Kc = [Products]^coefficients / [Reactants]^coefficients | varies |
| Relation Kp and Kc | Kp = Kc (RT)^(Delta n) | - |
| pH | pH = -log[H+] | Dimensionless |
| pOH | pOH = -log[OH-] | Dimensionless |
| Relation | pH + pOH = 14 (at 25 C) | - |
| Ionic product of water | Kw = [H+][OH-] = 10^-14 | mol^2/L^2 |
| Henderson-Hasselbalch | pH = pKa + log([Salt]/[Acid]) | - |
| Degree of dissociation | alpha = sqrt(Ka / C) (for weak acids) | Dimensionless |
| Buffer capacity | pH = pKa when [Salt] = [Acid] | - |
| Solubility product (Ksp) | For AB: Ksp = s^2 | mol^2/L^2 |
Chapter 7 - Redox Reactions
| Formula | Expression | Unit |
|---|---|---|
| Oxidation number rules | Sum of oxidation numbers = charge on species | - |
| n-factor (acids) | Basicity (number of replaceable H+ ions) | - |
| n-factor (bases) | Acidity (number of replaceable OH- ions) | - |
| Equivalent weight | Molar mass / n-factor | g/equiv |
Part 2 - Inorganic Chemistry
Inorganic Chemistry formulas are mostly periodic trends, rules, and relationships rather than mathematical equations.
Chapter 3 - Classification of Elements and Periodicity
| Property | Trend Along Period (Left to Right) | Trend Down Group |
|---|---|---|
| Atomic radius | Decreases | Increases |
| Ionisation enthalpy | Increases | Decreases |
| Electron gain enthalpy | Becomes more negative (generally) | Becomes less negative |
| Electronegativity | Increases | Decreases |
| Metallic character | Decreases | Increases |
| Non-metallic character | Increases | Decreases |
| Oxide nature | Basic to Amphoteric to Acidic | More basic |
Key relationships:
| Formula | Expression |
|---|---|
| Ionisation enthalpy | Energy to remove outermost electron from gaseous atom |
| Electron affinity | Energy change when electron is added to gaseous atom |
| Electronegativity (Pauling) | Based on bond dissociation energies |
| Electronegativity (Mulliken) | EN = (IE + EA) / 2 |
| Effective nuclear charge | Z(eff) = Z - sigma (Slater's rules) |
Chapter 4 - Chemical Bonding and Molecular Structure
| Concept | Formula / Rule |
|---|---|
| Formal charge | FC = Valence electrons - Non-bonding electrons - (1/2) Bonding electrons |
| Bond order | BO = (Bonding electrons - Anti-bonding electrons) / 2 |
| Bond order and stability | Higher bond order = shorter bond = stronger bond |
| Dipole moment | mu = q x d (charge x distance), unit: Debye |
| VSEPR shapes | AB2 = linear, AB3 = trigonal planar, AB4 = tetrahedral, AB5 = TBP, AB6 = octahedral |
| Hybridisation formula | H = (1/2)(V + M - C + A), where V = valence, M = monovalent, C = cation charge, A = anion charge |
| sp hybridisation | 2 regions, linear, 180 degrees |
| sp2 hybridisation | 3 regions, trigonal planar, 120 degrees |
| sp3 hybridisation | 4 regions, tetrahedral, 109.5 degrees |
| sp3d hybridisation | 5 regions, trigonal bipyramidal |
| sp3d2 hybridisation | 6 regions, octahedral, 90 degrees |
Chapter 8 - Hydrogen
| Property | Value / Formula |
|---|---|
| Hydrogen spectrum series | Lyman (UV), Balmer (visible), Paschen (IR), Brackett, Pfund |
| Hardness of water | Temporary: Ca(HCO3)2, Mg(HCO3)2 / Permanent: CaSO4, MgCl2 |
| Removal of temporary hardness | Boiling or adding Ca(OH)2 |
| Removal of permanent hardness | Na2CO3 or ion exchange |
Chapters 9-11 - s-Block and p-Block Elements
| Property | Key Facts |
|---|---|
| Alkali metals (Group 1) | ns^1 configuration, strongest reducing agents, flame colours: Li-crimson, Na-yellow, K-violet |
| Alkaline earth (Group 2) | ns^2 configuration, Be shows diagonal relationship with Al |
| Diagonal relationship | Li-Mg, Be-Al, B-Si share similar properties |
| p-Block general formula | ns^2 np^(1-6) |
| Boron | Electron-deficient, forms multicentre bonds |
| Carbon | Catenation property, forms 4 bonds |
| Nitrogen | Triple bond (N2), strong due to small size |
Practice any chapter on Padhaao
AI tutor for CBSE, ICSE & 15 state boards · 10 learning modes · 3 free chapters daily
Part 3 - Organic Chemistry
Chapter 12 - Organic Chemistry - Some Basic Principles
| Concept | Formula / Rule |
|---|---|
| Degree of unsaturation | DBE = (2C + 2 + N - H - X) / 2 (C = carbon, N = nitrogen, H = hydrogen, X = halogen) |
| Homologous series formula - Alkanes | CnH(2n+2) |
| Homologous series formula - Alkenes | CnH(2n) |
| Homologous series formula - Alkynes | CnH(2n-2) |
| IUPAC naming order | Prefix + Root word + Primary suffix + Secondary suffix |
| Inductive effect | -I (electron withdrawing): -NO2, -CN, -COOH, -F, -Cl, -Br, -OH |
| Inductive effect | +I (electron donating): -CH3, -C2H5, alkyl groups |
| Stability of carbocations | 3 degree > 2 degree > 1 degree > CH3+ |
| Stability of carbanions | CH3- > 1 degree > 2 degree > 3 degree |
| Stability of free radicals | 3 degree > 2 degree > 1 degree > CH3 radical |
| Hyperconjugation | Number of alpha-H atoms determines stability |
Chapter 13 - Hydrocarbons
| Hydrocarbon | General Formula | Example |
|---|---|---|
| Alkane | CnH(2n+2) | CH4 (methane), C2H6 (ethane) |
| Alkene | CnH(2n) | C2H4 (ethene), C3H6 (propene) |
| Alkyne | CnH(2n-2) | C2H2 (ethyne), C3H4 (propyne) |
| Cycloalkane | CnH(2n) | C3H6 (cyclopropane) |
| Benzene (arene) | CnH(2n-6) | C6H6 (benzene) |
Key reactions to remember:
| Reaction | What Happens |
|---|---|
| Markovnikov's rule | H adds to C with more H atoms, -OH/-X adds to C with fewer H atoms |
| Anti-Markovnikov (peroxide effect) | HBr adds opposite to Markovnikov in presence of peroxide |
| Wurtz reaction | 2RX + 2Na gives R-R + 2NaX (alkane synthesis) |
| Birch reduction | Benzene + Na/NH3(liq) gives 1,4-cyclohexadiene |
| Ozonolysis | Alkene + O3 then Zn/H2O gives two carbonyl compounds |
| Baeyer's test | Alkene decolourises KMnO4 (test for unsaturation) |
How to Memorise Chemistry Formulas Branch by Branch
Chemistry formulas come in three types, and each needs a different memorisation strategy.
Physical Chemistry - Practise with numbers. These are mathematical formulas. The only way to remember PV = nRT or Delta G = Delta H - T Delta S is to use them in numerical problems. Solve at least 5 problems per formula. After the third problem, you will stop looking at the formula sheet.
Inorganic Chemistry - Use visual maps. Periodic trends are best remembered as arrows on a periodic table. Draw a blank periodic table, mark arrows for ionisation enthalpy (up and right = increase), electron affinity, electronegativity, and atomic radius. One diagram replaces 20 lines of text.
Organic Chemistry - Write reactions, not just read them. Organic naming rules and reactions stick when you write them out on paper. Create a "reaction map" for each functional group: what goes in, what comes out, what reagent is needed.
5 Common Mistakes in Class 11 Chemistry
-
Confusing molarity and molality. Molarity uses volume of solution (litres), molality uses mass of solvent (kg). When temperature changes, molarity changes but molality does not.
-
Wrong sign in thermodynamics. w = -P Delta V has a negative sign. If gas expands, work is done by the system (negative w in IUPAC convention). Many students get the sign wrong and lose marks.
-
Forgetting exceptions in periodic trends. Ionisation enthalpy does not increase smoothly across a period. Be > B (full 2s), N > O (half-filled 2p stability). Examiners love testing these exceptions.
-
Mixing up +I and -I effects. Alkyl groups are +I (electron donating). Halogens, -NO2, -COOH are -I (electron withdrawing). Getting this backwards ruins your carbocation stability order.
-
Not balancing redox reactions properly. Use the oxidation number method or the ion-electron method consistently. Mixing both methods in one problem leads to errors.
Exam-Day Quick Revision Strategy
Minutes 1-10: Scan Physical Chemistry formulas. Focus on Thermodynamics (Delta G, Delta H, Delta S relationships) and Equilibrium (pH, Kp, Kc). These are the most commonly tested numerical topics.
Minutes 11-20: Review the periodic trends table and VSEPR shapes. Draw the hybridisation table from memory. Check if you remember formal charge calculation.
Minutes 21-30: Flip through Organic Chemistry. Verify you remember the general formulas (CnH2n+2 for alkanes, etc.), Markovnikov's rule, and the stability order of carbocations.
Minutes 31-35: Write out any formula you could not recall. The act of writing locks it in for the next 3-4 hours - exactly when you need it.
FAQ
Is Physical Chemistry harder than Organic or Inorganic?
It depends on your strengths. Physical Chemistry is calculation-heavy, so students good at Maths find it easier. Organic Chemistry requires spatial thinking and reaction logic. Inorganic requires memory but has clear patterns. Most students find Inorganic the hardest to retain because it feels like pure memorisation.
How many formulas should I know for the Class 11 Chemistry exam?
About 60-70 core formulas for Physical Chemistry, plus periodic trends, bonding rules, and organic naming conventions. The total count is less important than understanding when to use each formula.
Can I skip Organic Chemistry in Class 11?
No. Class 12 Organic Chemistry builds directly on Class 11 concepts (nomenclature, inductive effect, hyperconjugation, reaction mechanisms). Skipping it now means struggling with 5-6 chapters next year.
What is the most important formula in Class 11 Chemistry?
The mole concept (n = mass / molar mass) underpins almost every calculation in Chemistry. If you understand moles thoroughly, stoichiometry, gas laws, and solution chemistry all become easier.
How do I remember so many named reactions?
Group them by what they produce. Wurtz reaction makes alkanes. Ozonolysis breaks double bonds into carbonyls. Baeyer's test detects unsaturation. Organise by output, not by name, and they become logical instead of arbitrary.
Revise Smarter with Padhaao
Chemistry has three branches, hundreds of concepts, and dozens of formulas. Trying to revise everything from a textbook the night before an exam is stressful and inefficient.
Padhaao's AI tutor lets you practise chapter-wise with instant explanations. Ask it to quiz you on mole concept numericals, test your periodic trend knowledge, or walk you through organic naming step by step.
Free users get 3 chapters per day - enough to cover one branch per sitting. For full access to all chapters and unlimited practice, go Pro at Rs 99/month.
Want the full chapter with solved examples?
10 learning modes. Board-specific content. 3 free chapters every day.
Try it free