Chemistry

103 guides

Atoms and the periodic table

• Build an atom: protons, neutrons, electrons and ionsBuild an atom from protons, neutrons and electrons and see the element, mass number, charge, isotope and electron shells update, with worked examples.
• d orbitals: shapes, filling order and splittingWhat d orbitals are, the shapes of all five, how 3d and 4s fill in transition metals, and how d orbital splitting gives complexes their colour.
• Electron configuration calculator: any element or ionFree electron configuration calculator: full and noble gas configurations of any element or ion, with orbital box diagrams and the Cr and Cu exceptions.
• Electronic structure GCSE: shells, the first 20 elementsElectronic structure for GCSE Chemistry: how electrons fill shells, a table for the first 20 elements, shell diagrams, ions and the periodic table.
• Group 0: the noble gases, properties and trendsGroup 0 elements are the noble gases. Why they are unreactive, their boiling point trend with real data, uses of each gas, and how to predict properties.
• Ionisation energy: definition, trends and successive valuesFirst ionisation energy for A-level Chemistry: definition and equation, trends across period 3 and down group 2, and what successive values show.
• Properties of transition metals: the 4 key propertiesThe 4 properties of transition metals for A-level: complex ions, coloured ions, variable oxidation states and catalysis, all explained by the d sub-level.
• Relative isotopic mass: definition and examplesRelative isotopic mass for A-level Chemistry: the carbon-12 definition, how it differs from mass number and relative atomic mass, and mass spectra.
• The periodic table: how many elements, groups and periodsHow many elements are on the periodic table, how it is arranged into groups and periods, what it tells you about atoms, and who created it.
• What is an ion? Positive and negative ions explainedWhat an ion is, how atoms become positive or negative ions, how to work out an ion's charge and particles, ion names and formulae, with worked examples.
• What is relative atomic mass? Definition and calculationRelative atomic mass is the weighted average mass of an element's atoms compared with carbon-12. The definition and how to calculate it from isotopes.

Bonding and structure

• Diamond and graphite: structure, bonding and propertiesThe structure of diamond and graphite explained: bonding, why diamond is hard and graphite conducts, graphene and fullerenes, with GCSE exam answers.
• Hybridisation: sp, sp² and sp³ orbitals explainedHybridisation in chemistry: what sp³, sp² and sp orbitals are, how to work out an atom's hybridisation, bond angles, and sigma and pi bonds, with examples.
• Hydrogen bonding: what it is, examples and effectsWhat hydrogen bonding is, the conditions for it, how to draw it, examples such as water and ammonia, and why it raises boiling points and makes ice float.
• Intermolecular forces: the 3 types and boiling pointsThe three intermolecular forces: induced dipole, permanent dipole and hydrogen bonding, how they affect boiling points, and why water is unusual.
• Molecule builder: build molecules in 3D, check shapesFree 3D molecule builder: build molecules atom by atom, then read the formula, VSEPR shape, bond angles, polarity and a stability check with the reason.
• Shapes of molecules A-level Chemistry: VSEPR and anglesShapes of molecules for A-level Chemistry: electron pair repulsion, counting pairs, every shape from linear to octahedral with bond angles, and examples.
• States of matter simulation with a heating curveFree states of matter simulation: heat and cool real interacting particles, watch them melt, boil and freeze, and see the heating curve draw itself.
• What is a covalent bond? Covalent bonding with examplesWhat a covalent bond is, how to draw dot and cross diagrams, single, double and triple bonds, polar bonds, dative covalent bonds and covalent structures.
• What is an alloy? Why alloys are harder than pure metalsWhat an alloy is, why alloys are harder than pure metals, common alloys such as steel, brass, bronze and gold, and how to work out gold purity in carats.
• What is an ionic bond? Ionic bonding, lattices, propertiesWhat an ionic bond is, how ions form, dot and cross diagrams, working out formulae, giant ionic lattices and the properties of ionic compounds.
• Why are metals good conductors of electricity?Why metals are good conductors of electricity and heat: delocalised electrons in metallic bonding, how they carry charge, and why other materials don't.

Moles and quantities

• Atom economy formula: how to calculate it, with examplesThe atom economy formula, how to calculate percentage atom economy from a balanced equation, worked examples, atom economy versus yield, and practice.
• Balancing equations: step-by-step method and questionsHow to balance chemical equations step by step, with examples from easy to hard, brackets, the algebra method, ionic equations and 10 questions to try.
• Concentration calculator: molarity, mass and volumeFind the concentration of a solution in mol/dm³ (mol/L) or g/dm³, the moles or mass in it, or the mass to weigh out, with worked examples.
• Dilution calculator: C1V1 = C2V2 and serial dilutionsSolve C1V1 = C2V2 for any value, find how much water to add, and plan a serial dilution, with worked examples you can check in the calculator.
• Empirical formula calculator: from masses or percentagesFind the empirical formula from masses or percentages, and the molecular formula from Mr, with the moles and ratio table shown and worked examples.
• Grams to moles calculator: n = m ÷ M with stepsConvert grams to moles and back with n = m ÷ M, find molar mass, and turn moles into particles with the Avogadro constant, with examples.
• Limiting reactant calculator: find it in grams or molesFind the limiting reactant from masses or moles, the theoretical yield, and how much of the excess reactant is left, with a start, change and end table.
• Molar mass calculator: any formula, with percent compositionFind the molar mass of any chemical formula, including brackets, hydrates and ions, with each element's share by mass and worked examples to check.
• Molarity calculator: concentration, moles, mass and volumeFree molarity calculator: find molarity from moles or grams, the mass to weigh out, moles or volume, in mol/L or mol/dm³, with worked examples.
• Percent yield calculator: theoretical and actual yieldFree percent yield calculator: type the equation and your amounts to get the theoretical yield, then your percent yield from the mass you collected.
• Quantitative chemistry GCSE: every calculation explainedQuantitative chemistry for GCSE: conservation of mass, relative formula mass, moles, reacting masses, limiting reactants, concentration and yield.
• Relative formula mass (Mr): how to calculate itHow to calculate relative formula mass from a formula, with brackets and hydrates, the relative atomic mass formula for isotopes, examples and practice.
• Serial dilution calculator: tube by tube concentrationsPlan a serial dilution: the concentration of every tube, the total dilution factor and the solvent to add, from the stock and the step factor.
• Stoichiometry calculator: limiting reactant and yieldFind the limiting reactant, theoretical yield, percentage yield and atom economy from any equation, balanced for you, with worked examples to check.
• Titration calculations: step-by-step method and examplesHow to do titration calculations: moles from concentration and volume, mole ratios, mol/dm³ and g/dm³, mean titres, with GCSE and A-level examples.
• Volume equation in chemistry: gases, solutions and molesThe volume equations used in chemistry: gas volume = moles × 24 dm³, volume of solution = moles ÷ concentration, gas volumes from equations and pV = nRT.
• What is a mole in chemistry? Definition, formula, examplesA mole is 6.022 × 10²³ particles: the chemist's counting unit. Learn the mole formula, molar mass and Avogadro's number, with worked examples.

Reactions and electrolysis

• Bioleaching: how bacteria extract copper from oresWhat bioleaching is, how bacteria extract copper from low-grade ores, how the copper is recovered, and its advantages and disadvantages for GCSE Chemistry.
• Chemical equation balancer: with atom counts and workingFree chemical equation balancer: balance molecular, ionic and half equations, check the atom counts on both sides and see the algebra that balances them.
• Electrolysis diagram: labelled, with how to draw oneA labelled electrolysis diagram: power supply, anode, cathode and electrolyte, which way the ions move, how to draw it, and the products of common setups.
• Faraday constant: value, meaning and electrolysis examplesThe Faraday constant is the charge on one mole of electrons, 96 485 C/mol. Its value, F = Le, electrolysis calculations and ΔG = −nFE, with examples.
• Half equations: how to write and balance them, examplesHow to write half equations for oxidation and reduction: electrolysis at each electrode, displacement, balancing in acid with H₂O and H⁺, and combining.
• How to find oxidation numbers: rules and worked examplesHow to find oxidation numbers step by step: the rules, worked examples for compounds and ions, the exceptions, and using them to spot redox.
• Ionic equations: how to write them, with examplesWhat an ionic equation is, how to write one in four steps by removing spectator ions, and examples for neutralisation, precipitation and displacement.
• Neutralisation: equations, salts, pH and titrationsNeutralisation explained for GCSE: acid and base reactions, naming the salt, the ionic equation, pH, making a salt and titration calculations.
• Phytomining and bioleaching: how they extract copperWhat phytomining is, how plants extract copper from low-grade ores, how bioleaching works, getting copper from solution, and the pros and cons, for GCSE.
• Reactivity series GCSE: order, mnemonic and displacementThe reactivity series for GCSE Chemistry: the order of metals, a mnemonic to learn it, reactions with water and acid, displacement and extracting metals.
• What is electrolysis? How it works, with examplesElectrolysis uses electricity to split ionic compounds. How it works, the products at each electrode, real uses and calculations, with examples.
• What is oxidation? Definition, examples and OIL RIGWhat oxidation is: gain of oxygen, loss of hydrogen or loss of electrons. Redox reactions, half equations, oxidation numbers and everyday examples.

Acids and bases

• Brønsted-Lowry acid: definition, examples and pairsWhat a Brønsted-Lowry acid and base are, conjugate acid-base pairs, amphoteric water, strong and weak acids, with worked A-level examples.
• How to calculate pH: formula, examples and pH scaleHow to calculate pH from hydrogen ion concentration, for strong and weak acids and bases, with worked examples, the pH scale and what pH measures.
• Methyl orange colour change: acid, alkali and end pointMethyl orange is red in acid and yellow in alkali, turning orange between pH 3.1 and 4.4. See the colour change in titrations, and when to use it.
• pH calculator: strong and weak acids, bases and buffersFree pH calculator: the pH of strong and weak acids and bases from molarity, buffers by Henderson-Hasselbalch, and Ka from a measured pH, with steps.
• pKa: meaning, how to calculate it and pKa valuespKa explained for A-level Chemistry: Ka and pKa, converting between them, pKa values of common acids, pH from pKa, half-neutralisation and buffers.
• Titration calculator: concentration, titre and pH curveWork out an unknown concentration from a titration, step by step, then check it in a free virtual titration lab that plots the pH curve as you go.
• Titration practical: method, results and calculationsThe titration required practical: equipment, method, results table, concordant titres, working out the acid's concentration, errors and exam tips.

Energetics

• Bond enthalpy: definition and ΔH calculationsWhat bond enthalpy and mean bond enthalpy are, how to calculate ΔH from bonds broken minus bonds formed, examples, and why the answers are estimates.
• Born-Haber cycle: how to draw one and find lattice enthalpyWhat a Born-Haber cycle is, the enthalpy changes in it, how to draw one, and how to calculate lattice enthalpy, with worked examples for CsCl and MgCl₂.
• Enthalpy calculator: ΔH by Hess's law or bond enthalpiesFind the enthalpy change of a reaction from enthalpies of formation or combustion, combined equations or bond enthalpies, with working and worked examples.
• Enthalpy change formula: ΔH = −mcΔT ÷ n, with examplesThe enthalpy change formula ΔH = −mcΔT ÷ n from calorimetry: q = mcΔT, the sign of ΔH, neutralisation, combustion and dissolving examples, and Hess's law.
• Enthalpy of combustion: definition, values and calculationsStandard enthalpy of combustion: the definition, a table of values, measuring it with a calorimeter, why results come out low, and using it in Hess's law.
• Enthalpy of hydration: definition, trends and cyclesWhat enthalpy of hydration means, why it is always exothermic, how ion charge and size affect it, and how it gives the enthalpy of solution.
• Enthalpy of solution: definition, cycles and calculationsEnthalpy of solution explained: definition, the cycle with lattice and hydration enthalpies, calculations, calorimetry, and why dissolving can absorb heat.
• Exothermic reaction profile: how to draw and read oneHow to draw an exothermic or endothermic reaction profile, find the activation energy and energy change, and see what a catalyst does, with live graphs.
• Hess cycle: how to draw one and calculate enthalpy changesHow to draw a Hess cycle and use Hess's law: cycles with enthalpies of formation or combustion, the arrow rule, and worked examples with full working.

Rates and equilibrium

• Arrhenius equation: k = Ae^(−Ea/RT), graph and examplesThe Arrhenius equation k = Ae^(−Ea/RT) for A-level Chemistry: the terms and units, the ln k against 1/T graph, rearranging for Ea, T and A, and examples.
• Chemical reaction simulator: rates and collision theoryRun rate of reaction practicals as moving particles: change temperature, concentration, surface area and catalyst, and see why the rate changes.
• Dynamic equilibrium: meaning, Le Chatelier and KcDynamic equilibrium explained: reversible reactions, why concentrations stop changing, Le Chatelier's principle and the equilibrium constant Kc.
• Iodine clock reaction: method, equations and ordersHow the iodine clock reaction works, the equations, the method, and how to use clock times to find orders of reaction and activation energy.
• Kc equation: writing Kc expressions and calculating KcThe Kc equation for A-level Chemistry: writing the expression from a balanced equation, units, calculating Kc from equilibrium amounts, what changes Kc.
• Maxwell-Boltzmann distribution: curves and temperatureWhat the Maxwell-Boltzmann distribution shows, how to draw it, how temperature and catalysts change it, and why a small temperature rise speeds reactions.
• Partial pressure: formula, mole fraction and KpPartial pressure explained: Dalton's law, mole fraction × total pressure, how to write and calculate Kp for A-level Chemistry, with worked examples.
• Rate equation: rate = k[A]ᵐ[B]ⁿ, orders and units of kThe rate equation, rate = k[A]ᵐ[B]ⁿ, for A-level Chemistry: orders, finding orders from initial rates, the units of k, graphs and the slow step.
• Rate of reaction formula: mean rate, units and tangentsThe rate of reaction formula: mean rate from reactant used or product formed, units g/s, cm³/s and mol/s, rate from a tangent, the practical and examples.
• Rate of reaction graphs: how to read and compare themHow to read a rate of reaction graph: what the shape means, how temperature, concentration and catalysts change the curve, and how to sketch new curves.
• Rates and equilibrium calculator: rate equations and KcRate equations, orders from initial rates, activation energy with the Arrhenius equation, and Kc with an ICE table, all with step-by-step working.

Organic chemistry

• Acidified potassium dichromate: colour change and usesWhat acidified potassium dichromate(VI) does: the orange to green colour change, oxidising alcohols and aldehydes, reflux vs distillation, and tests.
• Amines and amides: structure, basicity and reactionsWhat an amine is, primary to tertiary amines, why phenylamine is a weak base, how amines are made and react, and amine vs amide, for A-level Chemistry.
• Condensation polymerisation: polyesters and polyamidesHow condensation polymerisation works, how it differs from addition polymerisation, polyesters, polyamides like nylon, and natural polymers.
• Displayed formula: what it is, how to draw one, examplesWhat a displayed formula is, how to draw one, and the displayed formulas of methane, propane, ethene, propene, ethanol, ethanoic acid, esters and more.
• Electrophilic addition: mechanism and major productsWhat electrophilic addition is, the mechanism for alkenes with HBr, bromine and sulfuric acid, carbocation stability, and how to predict the major product.
• Electrophilic substitution: benzene mechanism and examplesElectrophilic substitution of benzene explained: why benzene substitutes, the nitration and acylation mechanisms, directing groups and worked examples.
• Elimination reactions: mechanism, conditions, examplesWhat an elimination reaction is, the mechanism for halogenoalkanes with hot ethanolic KOH and for dehydrating alcohols, conditions, products and exam tips.
• Free radical substitution: mechanism and the three stepsThe free radical substitution mechanism for methane and chlorine: initiation, propagation and termination, why a mixture forms, and how CFCs destroy ozone.
• Friedel-Crafts acylation: mechanism, conditions, examplesFriedel-Crafts acylation of benzene for A-level: the conditions, how AlCl₃ makes the acylium ion, the mechanism step by step, and how to name the ketone.
• Hydroxynitrile: structure, naming, formation and isomersWhat a hydroxynitrile is, how to name one, how aldehydes and ketones form them with KCN by nucleophilic addition, racemic mixtures and KCN hazards.
• Incomplete combustion equation: how to write and balance itHow to write incomplete combustion equations for hydrocarbons, making carbon monoxide or soot, compared with complete combustion, with balanced examples.
• Nucleophilic addition-elimination: mechanism and reactionsThe nucleophilic addition-elimination mechanism for acyl chlorides with water, alcohols, ammonia and amines, anhydrides, and why aspirin is made with one.
• Nucleophilic addition: mechanism, NaBH₄ and KCNNucleophilic addition for A-level Chemistry: why aldehydes and ketones react this way, the curly arrow mechanism, reduction with NaBH₄ and KCN with acid.
• Nucleophilic substitution: mechanism, reactions, SN1 and SN2Nucleophilic substitution for A-level Chemistry: the mechanism with curly arrows, halogenoalkanes with OH⁻, CN⁻ and NH₃, reaction rates, and SN1 vs SN2.
• Organic synthesis map: reactions, reagents and routesAn organic synthesis map for A-level Chemistry: how the functional groups convert into each other, the reagents and conditions, and how to plan a route.
• Stereoisomers: E/Z isomerism and optical isomerismWhat stereoisomers are: E/Z isomerism with the CIP rules, optical isomerism, chiral centres, enantiomers and racemic mixtures, with worked examples.
• What is a homologous series? Definition and examplesA homologous series is a family of organic compounds sharing one general formula and functional group. Its features, with alkanes and alkenes as examples.

Analysis

• Separation techniques: filtration, distillation and moreThe 5 GCSE separation techniques: filtration, crystallisation, simple and fractional distillation and chromatography, how they work and when to use them.
• Test for hydrogen, oxygen, carbon dioxide and chlorineThe GCSE tests for gases: the squeaky pop test for hydrogen, a glowing splint for oxygen, limewater for carbon dioxide and damp litmus paper for chlorine.
• Tests for ions GCSE: flame tests, hydroxides and moreEvery GCSE Chemistry test for ions: flame test colours, metal hydroxide precipitates, and tests for carbonates, halides and sulfates, with worked examples.
• Thin-layer chromatography (TLC): method and Rf valuesHow thin-layer chromatography (TLC) works: the method, Rf values, why compounds separate, and how it compares with column and gas chromatography.

Courses

• Atomic structure course: atoms, isotopes and electron shellsAn interactive atomic structure course in 23 short sections: models of the atom, subatomic particles, isotopes, relative atomic mass, shells and ions.
• Chemical bonding course: ionic, covalent and metallicAn interactive chemical bonding course in 23 short sections: ionic, covalent and metallic bonds, structures, electronegativity, shapes and polarity.
• Organic chemistry course: alkanes, alkenes and isomersAn interactive organic chemistry course in 23 short sections: formulas, alkanes, alkenes, functional groups, naming, isomers, combustion and polymers.
• Reaction kinetics course: rates, collisions and catalystsAn interactive reaction kinetics course in 25 short sections: measuring rates, collision theory, energy profiles, catalysts and rate equations.