Chemistry Formula Sheet

Essential chemistry formulas and concepts

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MATH PHYSICS CHEMISTRY RSCIT REASONING COMPUTER SCIENCE BIOLOGY ENGLISH

Formula Collection

Atomic Structure

Bohr's Radius

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rₙ = 0.529 × n²/Z Å

Energy of Electron

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Eₙ = -13.6 × Z²/n² eV

Heisenberg's Principle

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Δx × Δp ≥ h/4π — can't know position & momentum simultaneously

Quantum Numbers

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n (shell 1-7), l (subshell 0 to n-1), mₗ (-l to +l), mₛ (±½)

Aufbau Principle

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1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p (energy order)

Hund's Rule

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Electrons fill degenerate orbitals singly before pairing

De Broglie Equation

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λ = h/mv — matter has wave nature

Periodic Table & Periodicity

Periodic Law

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Properties repeat with increasing atomic number

Group Trends

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Atomic size: increases down, decreases across; IE: decreases down, increases across

Electronegativity

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F > O > N > Cl (most electronegative); increases across, decreases down

Electron Affinity

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Most negative: Cl > F > Br > I; decreases down a group

Effective Nuclear Charge

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Zₑff = Z - S (Slater's rules for shielding constant)

Chemical Bonding

Bond Order

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Bond Order = (Bonding e⁻ - Antibonding e⁻)/2 (MO theory)

Octet Rule

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Atoms tend to gain/lose/share to achieve 8 valence e⁻

Formal Charge

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FC = Valence e⁻ - (Non-bonding e⁻ + Bond pairs/2)

VSEPR Theory

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2: Linear (180°), 3: Trigonal (120°), 4: Tetrahedral (109.5°), 5: Trig Bipyramidal, 6: Octahedral

Hybridization

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sp: 180° linear, sp²: 120° trigonal, sp³: 109.5° tetrahedral, sp³d: 90°/120°, sp³d²: 90°

Dipole Moment

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μ = q × d (vector sum — net μ depends on molecular symmetry)

Stoichiometry

Molarity

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M = moles of solute / liters of solution

Molality

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m = moles of solute / kg of solvent

Normality

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N = M × n-factor (n = H⁺/OH⁻/e⁻ exchanged)

Mole Concept

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1 mole = 6.022×10²³ particles, Molar mass = mass/1 mole

Percentage Composition

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Mass % = (mass of element / mass of compound) × 100

Empirical Formula

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Simplest whole-number ratio of atoms in a compound

Molecular Formula

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n × (Empirical Formula) where n = Molecular mass / Empirical mass

Thermochemistry

Enthalpy

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ΔH = Hₚ - Hᵣ (products - reactants)

Hess's Law

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ΔH for reaction = sum of ΔH of individual steps

Bond Enthalpy

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ΔH = Σ(Bond energies broken) - Σ(Bond energies formed)

Gibbs Free Energy

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ΔG = ΔH - TΔS, ΔG < 0 (spontaneous), ΔG > 0 (non-spontaneous)

Entropy

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ΔS = Sₚ - Sᵣ; Entropy increases with temperature and disorder

Electrochemistry

Nernst Equation

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E = E° - (RT/nF)ln(Q) or E = E° - (0.059/n)log(Q) at 298K

Faraday's Laws

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1st: m ∝ It; 2nd: m ∝ Equivalent weight; m = (M × I × t)/(n × F)

Cell EMF

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E°cell = E°cathode - E°anode (positive = spontaneous)

Conductivity

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κ = G × (cell constant), Λₘ = κ/C (molar conductivity)

Electrochemical Series

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Li > K > Ca > Na > Mg > Al > Zn > Fe > Sn > Pb > H > Cu > Ag > Au (reducing power)

Organic Chemistry

IUPAC Naming

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Prefix + Word Root + Suffix (e.g., meth-ane, prop-1-ene)

Homologous Series

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Alkanes: CₙH₂ₙ₊₂, Alkenes: CₙH₂ₙ, Alkynes: CₙH₂ₙ₋₂

Functional Groups

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-OH (alcohol), -CHO (aldehyde), -CO- (ketone), -COOH (acid), -NH₂ (amine)

Inductive Effect

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-I: electron withdrawing (F, Cl, NO₂), +I: electron donating (CH₃, alkyl)

Resonance

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Delocalization of π electrons — increases stability

Markovnikov's Rule

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H adds to carbon with more H (in HX addition to alkene)

Isomerism

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Structural (chain, position, functional) vs Stereoisomerism (geometric, optical)

Chemical Kinetics

Rate Law

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Rate = k[A]^m[B]^n (m,n = order of reaction)

First Order

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k = (2.303/t)log([A]₀/[A]ₜ), t₁/₂ = 0.693/k

Second Order

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k = (1/t)(1/[A]ₜ - 1/[A]₀), t₁/₂ = 1/k[A]₀

Arrhenius Equation

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k = Ae^(-Ea/RT), ln(k₂/k₁) = (Ea/R)(1/T₁ - 1/T₂)

Activation Energy

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Ea = Threshold energy - Average energy of reactants

Equilibrium

Equilibrium Constant

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Kc = [products]/[reactants] (raised to stoichiometric coefficients)

Kp and Kc

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Kp = Kc(RT)^Δn (Δn = gaseous moles products - reactants)

pH Scale

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pH = -log[H⁺], pOH = -log[OH⁻], pH + pOH = 14 at 298K

Henderson Equation

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pH = pKa + log([A⁻]/[HA]) (buffer solution)

Le Chatelier's Principle

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System shifts to counteract any applied change (T, P, concentration)

Ionic Product of Water

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Kw = [H⁺][OH⁻] = 1×10⁻¹⁴ at 298K

Quick Shortcuts & Tips

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Periodic table trends: Electronegativity increases across, decreases down

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Valency: Group number for 1-2, 8-group number for 13-18

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IUPAC: 'Meth, Eth, Prop, But, Pent, Hex, Hept, Oct, Non, Dec' - 1 to 10 carbons

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pH: <7 acidic, =7 neutral, >7 basic (alkaline)

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Electrochemical series: Li is best reducing agent, Au is worst

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VSEPR: 2=Linear, 3=Trigonal, 4=Tetrahedral, 5=BP, 6=Octahedral

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Markovnikov: 'The rich get richer' - H goes to C with more H

How to Use This Formula Sheet

Learn, Don't Memorize

Understand the derivation and application of each formula. Knowing why a formula works is more important than memorizing it.

Practice Application

Immediately after learning a formula, solve 5-10 problems using it. This reinforces learning and builds problem-solving skills.

Create Your Own Sheet

Copy formulas you frequently forget onto a physical sheet. The act of writing helps memory retention.

Regular Revision

Review formulas weekly. Use spaced repetition: next day, after 3 days, after 1 week, then monthly.

Common Formula Mistakes to Avoid

Unit Confusion

Always check units before applying formulas. Convert all measurements to consistent units (all in meters or all in centimeters).

Formula Misapplication

Ensure you're using the right formula for the given problem type. Don't force a formula that doesn't fit the situation.

Sign Errors

Pay attention to positive/negative signs, especially in physics and coordinate geometry formulas.

Approximation Errors

When using π = 22/7 or √2 = 1.414, be consistent. Don't mix exact and approximate values in the same calculation.

Practice with Formulas

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Quick Revision

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Study Guide

Detailed explanations of formulas and concepts

Previous Year Questions

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