THE LESSON LIBRARY / CHEMISTRY
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Newman Projections: Drawing Ethane
A Newman projection shows the arrangement around a chosen bond more clearly than a zigzag line drawing. Ethane is the simplest example: looking along its C–C bond makes the…
Explore lesson ChemistryLessonNickel-Based Rechargeable Cells
Nickel–cadmium and nickel–metal-hydride cells share a nickel oxyhydroxide positive electrode in alkaline electrolyte. They differ mainly in the negative electrode: cadmium metal…
Explore lesson ChemistryLessonNitrate Ion and Equivalent Bonds
Nitrate is a good test of Lewis electron accounting because a single diagram seems to give it one N=O double bond and two N–O single bonds. In the actual ion, the three oxygen…
Explore lesson ChemistryLessonNitration and Halogenation of Benzene
Benzene nitration and halogenation both replace a ring hydrogen through electrophilic aromatic substitution, but they use different electrophiles. Nitration commonly employs…
Explore lesson ChemistryLessonNitric Acid and Nitrate Chemistry
Nitric acid combines ordinary strong-acid behavior with significant oxidizing chemistry. In water it produces hydronium and nitrate to a very large extent, while under suitable…
Explore lesson ChemistryLessonNitric Acid by the Ostwald Process
Ammonia can be turned into nitric acid, making the Haber and Ostwald processes connected parts of a nitrogen-chemical value chain. The first Ostwald step is a very fast, strongly…
Explore lesson ChemistryLessonNitrogen and Its Compounds
Nitrogen gas makes up most of the atmosphere but does not react rapidly with ordinary materials at room temperature. Yet ammonia is a reactive base and nitrogen oxides…
Explore lesson ChemistryLessonNitrogen Fixation and the Haber Process
Nitrogen gas is abundant in air, but most organisms cannot directly use N₂ as a source of nitrogen for proteins and nucleic acids. Industrial nitrogen fixation converts N₂ into…
Explore lesson ChemistryLessonNitrogen Oxides and Tropospheric Ozone Formation
Near the ground, ozone is mainly a secondary pollutant formed through sunlight-driven chemistry involving nitrogen oxides and volatile organic compounds. A three-reaction…
Explore lesson ChemistryLessonNitrogen: The Main Gas in Air
Almost four-fifths of every breath is nitrogen, yet your body does nothing with it: the nitrogen you breathe in comes straight back out. Nitrogen is the most abundant gas in air…
Explore lesson ChemistryLessonNitrogen's Distinctive Chemistry
Nitrogen is the first member of group 15, but it is not just a smaller phosphorus atom. Its compact 2p orbitals form strong multiple bonds, and its valence shell lacks d…
Explore lesson ChemistryLabNMR chemical shift
A ¹H NMR spectrum: where signals appear, how big they are, and how they split.
Explore lesson ChemistryLessonNMR Pulse Sequences and Coherence
A simple one-pulse NMR experiment tips magnetisation away from B₀ and records the free induction decay. More informative experiments string together several pulses and carefully…
Explore lesson ChemistryLessonNMR Relaxation: T1 and T2
An RF pulse pushes nuclear magnetisation away from thermal equilibrium. Longitudinal magnetisation then returns toward the field direction while transverse magnetisation loses…
Explore lesson ChemistryLessonNo-Change Cases and Redox Identification
Many chemical changes involve no redox at all. A precipitate forms, an acid is neutralised or a substance dissolves, yet each element retains its oxidation number. A disciplined…
Explore lesson ChemistryLessonNoble Gases and Filled Outer Shells
Helium, neon and argon are commonly used where a gas with little ordinary chemical reactivity is helpful. Their outer electron shells are filled in a simple atomic model. Yet…
Explore lesson ChemistryLessonNoble Gases and Full Outer Shells
Noble gases provide a useful reference for stable electronic arrangements. Their neutral atoms have filled valence shells and usually react much less readily than neighbouring…
Explore lesson ChemistryLessonNoble Gases as Single Atoms
Oxygen, nitrogen and chlorine atoms pair up into molecules, but helium and argon atoms do not. A balloon full of helium contains countless separate helium atoms, each moving on…
Explore lesson ChemistryLessonNoble-Gas Compounds
Noble gases are famously unreactive, but “unreactive” is not “unable to form compounds.” Xenon forms fluorides and oxygen compounds when paired with strong oxidants and suitable…
Explore lesson ChemistryLessonNoble-Gas Shorthand
Writing every inner subshell becomes cumbersome for larger atoms. Noble-gas shorthand replaces a complete inner configuration with the symbol of the preceding noble gas in…
Explore lesson ChemistryLessonNodes and the Shapes of Box Wavefunctions
Look at the particle-in-a-box wavefunctions for n = 1, 2, 3 and 4 and a clear pattern appears: each new state has one more place where the wave crosses zero. These crossing…
Explore lesson ChemistryLessonNOESY and ROESY
Through-bond experiments reveal how atoms are connected, but they cannot tell a cis ring junction from a trans one or show how a chain folds back on itself. NOESY and ROESY…
Explore lesson ChemistryLessonNomenclature of Alcohols
An alcohol name tells the reader which carbon skeleton carries the hydroxyl group and where OH is attached. The -ol suffix usually identifies the principal alcohol group, while…
Explore lesson ChemistryLessonNomenclature of Ethers
An ether oxygen connects two carbon groups rather than bearing hydrogen. Common names often list the groups on either side of oxygen, but systematic names commonly treat the…
Explore lesson ChemistryLessonNomenclature of Phenols
Phenol names begin with direct attachment of OH to an aromatic ring. The OH-bearing ring carbon is conventionally carbon 1 when phenol is the parent, and other groups receive…
Explore lesson ChemistryLessonNon-metal Oxides Are Acidic
Many oxides of non-metals behave differently from common basic metal oxides. Carbon dioxide can acidify water weakly; sulfur dioxide can acidify it more noticeably under suitable…
Explore lesson ChemistryLessonNon-Metallic Character and Position
Non-metals are concentrated toward the upper right of the periodic table, apart from hydrogen's special position. Across a main-group period, non-metallic character generally…
Explore lesson ChemistryLessonNon-metals Combining with Oxygen
Carbon, sulfur and hydrogen can combine with oxygen, producing oxides with distinct formulas and properties. These reactions often release energy, yet the product depends on the…
Explore lesson ChemistryLessonNon-metals Gain or Share Electrons
Non-metals commonly appear as negative ions in salts with reactive metals or share electrons in covalent substances. The two outcomes should not be merged into one story.…
Explore lesson ChemistryLessonNon-Stoichiometry and Oxygen Partial Pressure
Many oxides tolerate a range of compositions rather than one exact integer formula. A specimen written MO₂−δ has an oxygen deficit δ relative to the reference MO₂ lattice, while…
Explore lesson ChemistryLessonNonadiabatic Transitions
Most reaction-path calculations assume nuclei move on one electronic potential-energy surface. This Born–Oppenheimer picture works well when the electronic state remains clearly…
Explore lesson ChemistryLessonNoncovalent Interaction Energies
A weakly bound dimer may differ from its separated fragments by only a few kilojoules per mole. At that scale, a small basis-set artifact or a neglected entropy term can change…
Explore lesson ChemistryLessonNonheme Iron Enzymes
Haem is not the only way to activate oxygen with iron. Many enzymes bind iron directly to amino-acid side chains, with no porphyrin ring at all. These nonheme iron enzymes…
Explore lesson ChemistryLessonNonstandard Galvanic Cells
Real galvanic cells rarely begin with every solute at standard activity and every gas at standard pressure. Their actual open-circuit potential follows the Nernst equation for…
Explore lesson ChemistryLessonNonstoichiometric Defects
Some solids tolerate small departures from an ideal integer composition while retaining a crystal framework. Such nonstoichiometry often involves vacancies, interstitials and…
Explore lesson ChemistryLessonNormalisation of Wavefunctions
The Born interpretation says that |ψ|² dτ is the probability of finding a particle in a small volume. Since the particle must be found somewhere, all these probabilities must add…
Explore lesson ChemistryLessonNormalised Box Wavefunctions
The boundary conditions fix the shape of each box wavefunction as A sin(nπx/L) but leave the amplitude A undetermined. To use the wavefunctions for predictions — the probability…
Explore lesson ChemistryCollectionNuclear and Radiochemistry
Study Nuclear and Radiochemistry with 30 free lessons, worked examples, and answered practice questions.
Explore lesson ChemistryLessonNuclear and Radiochemistry: Unit Review
Nuclear and radiochemistry joins quantum structure, mass-energy, reaction probabilities, chemical separations and measurement. The same isotope can be described by its position…
Explore lesson ChemistryLessonNuclear Change Versus Chemical Change
Chemical reactions and nuclear transformations both make changes we can observe, but they act on different parts of the atom. A chemical reaction rearranges bonds and electrons…
Explore lesson ChemistryLessonNuclear Charge and Electron Attraction
Adding a proton increases the nucleus's positive charge, but it does not always mean every electron is held closer than before. Electrons also occupy different shells and repel…
Explore lesson ChemistryLessonNuclear Chemistry Formulae
Nuclear formulae describe statistical transformations of large atom populations and energy associated with mass differences. The same letter *A* may mean mass number in nuclide…
Explore lesson ChemistryLessonNuclear Chemistry Terms
Nuclear chemistry examines changes in atomic nuclei, whereas ordinary chemical reactions mostly rearrange electrons and bonds. Its vocabulary often appears in medicine, energy…
Explore lesson ChemistryCollectionNuclear Concepts: Radioactivity
Study Nuclear Concepts: Radioactivity with 30 free lessons, worked examples, and answered practice questions.
Explore lesson ChemistryLessonNuclear Fission as a Chain Process
In nuclear fission, a heavy nucleus splits into smaller nuclei and releases energy. Some fissions also release neutrons, which can induce further fissions. That makes a chain…
Explore lesson ChemistryLessonNuclear Fusion and Stellar Energy
Fusion joins light nuclei rather than splitting a heavy one. In suitable reactions, the products have lower total mass-energy than the starting system, and the difference emerges…
Explore lesson ChemistryLessonNuclear Half-Life Data
A radioactive half-life belongs to a specific nuclear state, not just an element name. Isotopes of the same element can have radically different decay modes and lifetimes; an…
Explore lesson ChemistryLessonNuclear Reactions and Their Notation
Nuclear reactions alter nuclei through collisions rather than spontaneous decay alone. A projectile may strike a target, after which an outgoing particle and residual nucleus…
Explore lesson ChemistryLessonNuclear Spin and the Magnetic Field
Nuclear magnetic resonance (NMR) spectroscopy is the single most powerful technique for working out the structure of an organic molecule. It can reveal how many different…
Explore lesson ChemistryLessonNucleation and Growth
Nanoparticle size is shaped early, when molecular precursors first form tiny clusters. Those clusters must overcome an interfacial cost before they grow into persistent…
Explore lesson ChemistryLessonNucleation and Growth of Quantum Dots
Dot size determines much of a quantum dot's optical response, so a useful synthesis must control both average size and the spread of sizes. The LaMer picture describes how an…
Explore lesson ChemistryLessonNucleation and Metastability
A liquid can remain supercooled and a solution can remain supersaturated even though another phase has lower Gibbs energy. The reason is that a tiny new-phase cluster creates an…
Explore lesson ChemistryLabNucleic acid base pairing
Type a DNA sequence and see the double helix with A–T and G–C base pairs.
Explore lesson ChemistryLessonNucleophiles, Electrophiles and Orbital Control
The statement “nucleophiles attack electrophiles” identifies the partners but not always the approach direction or rate. Frontier molecular orbital reasoning adds another layer…
Explore lesson ChemistryLessonNucleophilic Acyl Substitution
An acyl derivative R–C(=O)–Y has two mechanistic features: its carbonyl carbon attracts nucleophiles, and Y can leave after attack. The common result is substitution of Y by a…
Explore lesson ChemistryLessonNucleophilic Acyl Substitution: Addition–Elimination
Carboxylic acid derivatives share the structural motif R–C(=O)–Z. Their characteristic reaction replaces Z with a nucleophile while retaining a carbonyl in the product. The net…
Explore lesson ChemistryLabNucleophilic addition to carbonyl
A nucleophile attacks the δ+ carbon of a C=O group; the carbon changes from flat to tetrahedral.
Explore lesson ChemistryLessonNucleophilic Addition to Carbonyls: The General Mechanism
Nucleophilic addition is a foundation for making alcohols, cyanohydrins, hemiacetals and many carbon–carbon bonds. The central event is always a controlled redistribution of an…
Explore lesson ChemistryLessonNucleophilic Addition: General Mechanism
The standard reaction pattern for an aldehyde or ketone is addition across its C=O bond. A nucleophile makes a bond to carbon, and the pi electrons move toward oxygen. Proton…
Explore lesson ChemistryLessonNucleophilic Aromatic Substitution
An ordinary aryl halide does not behave like a primary alkyl halide in a normal SN2 reaction: backside attack at an sp² ring carbon is geometrically and electronically difficult.…
Explore lesson ChemistryLessonNucleophilic Reactions of Amines
The same nitrogen lone pair that makes an amine basic also makes it a nucleophile. It can form a new bond to an electron-poor carbon or other electrophilic center. Whether the…
Explore lesson ChemistryLessonNucleophilic Substitution Overview
The polarized bond of a haloalkane makes its halogen-bearing carbon a potential target for an electron-pair donor. In nucleophilic substitution, a nucleophile forms a new bond to…
Explore lesson ChemistryLessonNucleophilicity versus Basicity
A species with a lone pair can do two different things. It can attack an electrophilic carbon and form a new bond, acting as a nucleophile, or it can pull off a proton, acting as…
Explore lesson ChemistryLessonNucleosides and Nucleotides
DNA and RNA are built from nucleotides, but a nucleotide itself has several parts: base, sugar and phosphate. The way nucleotides connect gives the chain direction and leaves the…
Explore lesson ChemistryLessonNuclide Notation
One compact symbol can encode an element, its nucleon count and its ionic charge. The information is useful only if each number is read in the correct position. Nuclide notation…
Explore lesson ChemistryLessonNuclide Symbols and Nuclear Counting
Radioactive-decay equations use a compact symbol that records a nucleus's proton and nucleon counts. Reading it correctly is more important than memorising a long list of…
Explore lesson ChemistryLessonNudged Elastic Band and String Methods
If reactant and product structures are known but the route between them is not, varying one bond length may be too restrictive. The bond may bend, a proton may shift, or an…
Explore lesson ChemistryLessonNumber of Particles to Mass
A particle count can be turned into a mass even though no balance could weigh those particles one by one. Divide the count by the number of entities per mole, then multiply by…
Explore lesson ChemistryLessonNumber of Particles to Moles
Chemists rarely know the number of particles in a sample directly, but sometimes a question gives it — for example, "a sample contains 3.01 × 10²² molecules". To use that…
Explore lesson ChemistryLessonNumber-Average Molar Mass
The number-average molar mass treats every polymer molecule as one vote, regardless of length. It is the natural average when a measurement responds to the number of chains or…
Explore lesson ChemistryLessonNumbering a Parent Chain
Once a parent carbon chain is chosen, the carbon atoms need numbers. A correct chain with incorrect numbering can name a different isomer. Compare both directions and give the…
Explore lesson ChemistryLessonNumbering Chains and Locants
Once a parent chain is selected, it can usually be numbered from either end. The correct direction gives low locants according to an ordered hierarchy, not simply the smallest…
Explore lesson ChemistryLessonNutrients and Eutrophication
Nitrogen and phosphorus are needed to make proteins, nucleic acids and cell membranes. A lake or estuary with too little of either cannot support rapid algal growth; an excessive…
Explore lesson ChemistryLessonO–H Absorptions in Alcohols and Carboxylic Acids
Of all the bands in an infrared spectrum, the O–H stretch is one of the easiest to spot. In an alcohol it is a broad, rounded trough centred near 3300 cm⁻¹; in a carboxylic acid…
Explore lesson ChemistryLessonObservations and Inferences
Imagine you walk into a kitchen and see a glass with fizzing liquid and a spoon beside an open box of baking soda. You might immediately think, "Someone mixed baking soda with…
Explore lesson ChemistryLessonObservations as Evidence
An observation is evidence only when its conditions are known. “A pale green precipitate formed” is a description; “Fe(OH)₂ formed from Fe²⁺” is an inference that requires…
Explore lesson ChemistryLessonObtaining Pure Salt from Rock Salt
Rock salt is mined from underground deposits and spread on icy roads in winter. It looks grey or brown because it is not pure: it is a mixture of sodium chloride (common salt)…
Explore lesson ChemistryLessonOcean Acidification
The ocean absorbs part of the carbon dioxide added to the atmosphere. That uptake changes seawater carbonate chemistry: hydrogen-ion concentration rises, pH falls, and carbonate…
Explore lesson ChemistryLessonOctahedral and Square-Pyramidal Shapes
Six electron domains in a basic VSEPR model occupy an octahedral arrangement. When all six are bonds, as in SF₆, the molecular shape is octahedral. When one is a lone pair, as in…
Explore lesson ChemistryLessonOctahedral CFSE for d¹ to d³ Ions
The first three d electrons provide the cleanest CFSE examples. An octahedral t₂g set has three equal-energy orbitals, so d¹, d² and d³ ions can place every electron in a…
Explore lesson ChemistryLessonOctahedral CFSE for d⁴ to d⁷: High-Spin Cases
The fourth d electron creates the first genuine octahedral spin choice. It can pair with a t₂g electron or occupy an empty e_g orbital. When Δₒ is small compared with the…
Explore lesson ChemistryLessonOctahedral CFSE for d⁴ to d⁷: Low-Spin Cases
When the octahedral gap grows large, putting an electron in e_g can cost more than pairing it in t₂g. The resulting low-spin d⁴ through d⁷ configurations have fewer unpaired…
Explore lesson ChemistryLessonOctahedral CFSE for d⁸ to d¹⁰ Ions
Once six d electrons fill t₂g, additional electrons must enter e_g. For octahedral d⁸ through d¹⁰, a large or small Δₒ no longer creates the familiar pair-versus-promotion choice…
Explore lesson ChemistryLessonOctahedral d-Orbital Splitting
Six ligands in an ideal octahedral complex approach a metal along three Cartesian axes. This particular geometry separates five d orbitals into a lower group of three and an…
Explore lesson ChemistryLessonOctahedral Site Preference Energy
Some ionic crystals offer a metal cation two kinds of oxygen environment: tetrahedral sites with four near neighbours and octahedral sites with six. A d ion can gain a different…
Explore lesson ChemistryLessonOctet Exceptions and Expanded Valence
The octet rule is a useful pattern for many main-group Lewis structures, but it is not a law that every atom must obey. Boron compounds can be electron deficient, odd-electron…
Explore lesson ChemistryLessonOdd-Electron Molecules and Radicals
Most introductory Lewis examples use pairs of electrons throughout. If a species has an odd number of valence electrons, an all-paired drawing cannot possibly account for it.…
Explore lesson ChemistryLessonOdour and Other Clues
Your senses often notice a chemical change before any instrument does. Milk that has gone off smells sour. Toast that is burning gives a sharp, acrid smell. A firework bangs.…
Explore lesson ChemistryLessonOdour, Taste and Safe Observation
Smell and taste are powerful senses. Many substances can be recognised instantly by their odour — vinegar, perfume, gas leaks — and people once identified chemicals by taste.…
Explore lesson ChemistryLessonOlefin Metathesis Mechanism
How can a catalyst cut two C=C bonds and rejoin the pieces? In 1971 Yves Chauvin proposed that metathesis runs through a metal–carbon double bond, a metal alkylidene, and a…
Explore lesson ChemistryLessonOlefin Metathesis: The Net Reaction
Most reactions of alkenes add something across the double bond. Olefin metathesis is different: it cuts C=C bonds and stitches the fragments back together in new combinations.…
Explore lesson ChemistryLessonOlfactory Indicators
Most indicators are read with the eyes, but some can be read with the nose. An olfactory indicator is a substance whose smell changes in acidic or basic conditions. Onion…
Explore lesson ChemistryLessonOlivine and Spinel Cathode Structures
Two cathodes can both insert lithium yet move it through very different crystal networks. Lithium iron phosphate, LiFePO₄, has an olivine framework, while lithium manganese…
Explore lesson ChemistryLessonOne pH Unit Means a Tenfold Change
A pH difference is easy to read but easy to misinterpret. The numbers are logarithms, so a one-unit difference means a factor of ten in hydronium activity, not an additive…
Explore lesson ChemistryLessonOne-Component Phase Diagrams
A one-component pressure–temperature phase diagram maps which phase of a pure substance is stable under equilibrium conditions. Solid, liquid and vapour occupy regions separated…
Explore lesson ChemistryLessonOne-Dimensional Selective NMR
Two-dimensional NMR is powerful, but a carefully chosen one-dimensional selective experiment can answer a focused question quickly. Irradiating one narrow resonance can reveal…
Explore lesson ChemistryLessonOne-Factor-at-a-Time Limitations
Changing one chemical condition at a time feels controlled: adjust temperature, choose the best value, then adjust solvent, then catalyst loading. The approach can answer focused…
Explore lesson ChemistryLessonOne-Group C–X Disconnections
Carbon–heteroatom bonds often provide recognizable retrosynthetic cuts because common reactions join carbon electrophiles to oxygen or nitrogen nucleophiles. Ethers, esters…
Explore lesson ChemistryLessonOne-Letter Element Symbols
The simplest chemical symbols are single letters. Some of the most important elements in chemistry and in living things — hydrogen, carbon, nitrogen and oxygen — have one-letter…
Explore lesson ChemistryLessonOnset of Precipitation
Suppose a solution contains a metal ion and a precipitating reagent is added drop by drop. At first nothing appears; then, at a definite moment, the first cloudiness forms.…
Explore lesson ChemistryLessonOpen Systems: When Mass Seems to Change
An open beaker can lose mass when gas escapes or gain mass when it absorbs oxygen from air. Neither result overturns conservation. It shows that the beaker and its contents are…
Explore lesson ChemistryLessonOpen, Closed and Isolated Systems
Thermodynamic systems are often classified by what crosses their boundaries. An open system can exchange matter and energy; a closed system can exchange energy but not matter; an…
Explore lesson ChemistryLessonOperando Catalyst Characterization
Catalysts can change while they work. A metal may oxidise, a nanoparticle may reshape, a ligand may dissociate and an electrode may form a new surface layer. A before-and-after…
Explore lesson ChemistryLessonOperando Measurements
Many important energy-material states exist only while a device works. A battery electrode may expand on charge and relax after disassembly. A solar absorber may change its ion…
Explore lesson ChemistryLessonOperators and Observables
In classical mechanics, momentum and energy are numbers that can be calculated directly from position and velocity. In quantum mechanics the state is a wavefunction, so we need a…
Explore lesson ChemistryLessonOptical Absorption and Band-Gap Measurement
An absorption spectrum can reveal when photons have enough energy to excite electrons into accessible states. That threshold is related to a semiconductor's electronic structure…
Explore lesson ChemistryLessonOptical Activity and Specific Rotation
Enantiomers share almost every physical property: the same melting point, boiling point, density and solubility in ordinary solvents. How, then, can anyone tell a bottle of one…
Explore lesson ChemistryLessonOptical Isomerism in Complexes
Some coordination complexes occur as left- and right-handed forms. The two forms contain the same atoms, bonds and many physical properties, but one cannot be rotated into exact…
Explore lesson ChemistryLessonOptical Isomerism in Haloalkanes
Some haloalkanes have a tetrahedral carbon attached to four different groups. Such a carbon can be a stereocenter, giving two non-superimposable mirror-image structures called…
Explore lesson ChemistryLessonOrbital Box Diagrams
Electron-configuration notation reports how many electrons occupy each subshell, while orbital-box diagrams show how those electrons are distributed among individual orbitals and…
Explore lesson ChemistryLessonOrbital Contribution and Quenching
The spin-only formula often works well for first-row metal complexes, yet some measured moments are distinctly larger. The difference can arise because electrons carry orbital as…
Explore lesson ChemistryLessonOrbital Contributions and Deviations from Spin-Only Values
The spin-only formula is an approximation, not a law that every transition-metal compound must obey. High-spin Co²⁺ complexes frequently show moments larger than the…
Explore lesson ChemistryLessonOrbital Energies and Koopmans' Theorem
Hartree–Fock produces orbital eigenvalues, and the highest occupied value is often compared with the energy needed to remove an electron. Koopmans' theorem gives a simple…
Explore lesson ChemistryLabOrbital filling (Aufbau/Pauli/Hund)
Electrons fill orbital boxes one by one, following the Aufbau, Pauli and Hund rules.
Explore lesson ChemistryLabOrbital shapes
Real hydrogen orbitals drawn as clouds of dots, with their nodes.
Explore lesson ChemistryLessonOrbital Size and Penetration
Orbital size is not captured by one radius, and orbitals within the same shell can differ in how closely their electron density approaches the nucleus. This near-nucleus…
Explore lesson ChemistryLessonOrbital Symmetry and the Woodward–Hoffmann Rules
Two reactions can have identical atom and electron counts yet prefer different stereochemical paths. The Woodward–Hoffmann rules explain this by following the symmetry of…
Explore lesson ChemistryLessonOrder of Steps in Aromatic Synthesis
In a multisubstituted aromatic target, the order in which groups enter the ring determines where later electrophiles attack. A methyl or amino group often directs new…
Explore lesson ChemistryLessonOrdinary Differential Equation Models
Stoichiometry tells how each reaction changes species amounts, and rate laws tell how quickly each reaction proceeds. Together they form ordinary differential equations (ODEs)…
Explore lesson ChemistryLessonOre Concentration Methods
Before a chemical reaction extracts metal, a plant often separates valuable mineral from gangue. Three broad techniques exploit different properties: froth flotation exploits…
Explore lesson ChemistryLessonOrganic and Inorganic Chemistry
On the last page you met the branches of chemistry. Two of the oldest are organic and inorganic chemistry. The dividing line between them is the element carbon. This page…
Explore lesson ChemistryLessonOrganic Basics Integrated Problems
The strongest organic answers connect several skills instead of treating each page as an isolated rule. A name encodes connectivity; connectivity identifies functional groups and…
Explore lesson ChemistryLessonOrganic Chemistry Basic Principles Review
Organic chemistry basic principles form a connected method. A molecular formula supplies atom counts; a structural formula supplies connectivity; a systematic name communicates…
Explore lesson ChemistryLessonOrganic Chemistry Practice
Organic chemistry tests the ability to move among formula, connectivity, three-dimensional structure and reaction pathway. A formula alone does not identify a molecule; a product…
Explore lesson ChemistryCollectionOrganic Chemistry: Basic Principles
Study Organic Chemistry: Basic Principles with 45 free lessons, worked examples, and answered practice questions.
Explore lesson ChemistryLessonOrganic Chemistry: Definitions and Scope
"Organic" in a supermarket means food grown without synthetic pesticides. In chemistry the word means something completely different: organic chemistry is the chemistry of carbon…
Explore lesson ChemistryCollectionOrganic Conversions, Isomerism and Reasoning
Study Organic Conversions, Isomerism and Reasoning with 80 free lessons, worked examples, and answered practice questions.
Explore lesson ChemistryLessonOrganic Conversions, Isomerism and Reasoning: Unit Review
Organic reasoning combines three questions: how can one compound be converted into another, what distinct structures are possible, and why does a proposed reagent make a…
Explore lesson ChemistryCollectionOrganic Mechanisms and Named Reactions
Study Organic Mechanisms and Named Reactions with 100 free lessons, worked examples, and answered practice questions.
Explore lesson ChemistryLessonOrganic Mechanisms Review
Named organic reactions can seem like a long list, but their mechanisms reuse a smaller set of ideas. Nucleophiles attack electron-poor centres, leaving groups depart, proton…
Explore lesson ChemistryLessonOrganic Naming Error Clinic
Organic naming mistakes are usually traceable to one of three decisions: the parent path, the numbering direction or the suffix-defining group. A systematic error clinic checks…
Explore lesson ChemistryLessonOrganic Photovoltaic Materials
Organic solar cells use carbon-rich molecules or polymers whose optical gaps, energy levels and processing can be tuned through chemistry. Their absorbers may be printed or…
Explore lesson ChemistryLessonOrganic Reaction Terms
Organic reactions are often named by what changes in the product and by how electrons move along a pathway. These are related but different levels of description. A substitution…
Explore lesson ChemistryLessonOrganic Reactions: Addition and Substitution
Addition and substitution are two common reaction patterns in carbon chemistry. Ethene can add atoms across C=C, while methane can undergo replacement of an H by a halogen under…
Explore lesson ChemistryLessonOrganic Reactions: Oxidation and Esterification
Two reactions involving ethanol can have very different outcomes. Oxidation changes the bonding at one carbon and may retain its two-carbon skeleton; esterification joins…
Explore lesson ChemistryLessonOrganic Structure and Reactions Map
Organic chemistry contains many molecules, but a small set of structural and mechanistic patterns organizes their behavior. A concept map begins with connectivity and functional…
Explore lesson ChemistryLessonOrganic Structure Terms
Organic structural language explains why one molecular formula can describe different substances. An alcohol and an ether may have identical elemental counts but different…
Explore lesson ChemistryCollectionOrganic Synthesis and Mechanisms
Study Organic Synthesis and Mechanisms with 70 free lessons, worked examples, and answered practice questions.
Explore lesson ChemistryLessonOrganic Synthesis and Mechanisms: Unit Review
This unit connects three ways of reorganising organic molecules. Carbonyl chemistry uses the electrophilicity of C=O, enolate chemistry turns the alpha carbon into a nucleophile…
Explore lesson ChemistryLessonOrganic Synthesis Mechanism Audit
A plausible-looking synthesis can still contain an impossible intermediate, a misplaced carbon, or the wrong major regioisomer. A mechanism audit catches these errors before the…
Explore lesson ChemistryLessonOrganic Synthesis: The Big Picture
Organic synthesis is the deliberate construction of a molecule with specified connectivity and often specified stereochemistry. A target may be a biological probe, a polymer…
Explore lesson ChemistryLessonOrganohalogen Compounds
Replacing hydrogen in an organic compound with fluorine, chlorine, bromine, or iodine creates an organohalogen compound. A formula alone may not reveal how it reacts: the key…
Explore lesson ChemistryLessonOrganometallic Addition: Grignard and Organolithium Reagents
Hydride reduction adds hydrogen to carbonyl carbon; organometallic addition can add an entire carbon fragment. Reagents such as RMgX and RLi behave as sources of a strongly…
Explore lesson ChemistryCollectionOrganometallic Chemistry and Catalysis
Study Organometallic Chemistry and Catalysis with 50 free lessons, worked examples, and answered practice questions.
Explore lesson ChemistryLessonOrganometallic Chemistry and Catalysis: Unit Review
Organometallic chemistry becomes most useful when its separate ideas work together. A catalyst's oxidation state, electron count and coordination geometry affect which substrate…
Explore lesson ChemistryLessonOrganometallic Formation from Halides
An alkyl or aryl halide can be converted into an organomagnesium reagent by reaction with magnesium in a suitable dry ether solvent. The product, commonly written RMgX, is a…
Explore lesson ChemistryLessonOrgel Diagrams for d¹, d⁴, d⁶ and d⁹
The D-ground-term Orgel diagram is the simplest many-electron term diagram. It covers free-ion d¹, d⁴, d⁶ and d⁹ ground terms in the weak-field, high-spin setting. The D term…
Explore lesson ChemistryLessonOrgel Diagrams for d², d³, d⁷ and d⁸
Unlike a D ground term, an F ground term produces three octahedral components. Moreover, the same d configurations also possess a higher P term of the same spin multiplicity. The…
Explore lesson ChemistryLessonOrigins of Magnetism in Complexes
Electronic spectra describe energy differences; magnetism probes how electronic states respond to an applied field. Both arise from the same d-electron arrangement. Unpaired…
Explore lesson ChemistryLessonOrtho, Meta and Para Directing
Once benzene has one substituent, a second electrophile can enter at more than one ring position. The positions next to the first group are ortho, those one carbon farther away…
Explore lesson ChemistryLessonOrthogonality of Box Wavefunctions
The particle in a box has an infinite ladder of wavefunctions, one for each quantum number n. These functions are not independent of each other in an arbitrary way: any two…
Explore lesson ChemistryLessonOsmosis and Osmotic Pressure
Place pure water and a solution on opposite sides of a membrane that allows water to pass but holds back the solute. Water tends to move toward the solution side until another…
Explore lesson ChemistryLabOsmosis and reverse osmosis
Water flows through a membrane into a solution until the liquid height pushes back. Apply pressure to reverse it.
Explore lesson ChemistryLessonOsmotic Pressure and Particle Factor
A semipermeable membrane can pass solvent but restrict a dissolved solute. Solvent tends to move toward the side with greater effective dissolved-particle concentration. For a…
Explore lesson ChemistryLessonOsmotic Pressure and the van 't Hoff Equation
Place pure solvent on one side of a membrane and a dilute solution on the other. If the membrane allows solvent through but blocks solute, solvent tends to enter the solution.…
Explore lesson ChemistryLessonOther Configuration Exceptions
Chromium and copper are memorable, but they are not the only elements whose ground-state configurations resist a simple diagonal filling list. Close subshell energies and…
Explore lesson ChemistryLessonOther Molar-Mass Averages
Number and weight averages are common, but they do not exhaust the ways to summarise a polymer's molar-mass distribution. The z-average emphasises very large chains even more…
Explore lesson ChemistryLessonOutliers and Data Exclusion
An unexpected point can result from a spilled sample, mislabeling, instrument carryover or a real chemical event. Deleting it because it weakens a preferred claim turns…
Explore lesson ChemistryLessonOverall Yield Across Several Steps
A multistep synthesis can lose material at each stage. For a simple linear route where every step yield is defined relative to the material entering that step, multiply the yield…
Explore lesson ChemistryLessonOverlapping Polyprotic Equilibria
The tidy stage-by-stage picture of polyprotic titrations depends on one condition: the stepwise acid constants must be well separated. When successive pKa values lie within one…
Explore lesson ChemistryLessonOverpotential and Its Sources
An equilibrium electrode potential describes a reversible state with no net current. Driving appreciable current generally requires the electrode potential to depart from that…
Explore lesson ChemistryLessonOverpotential and Polarization
The standard potentials in data tables predict that water should split at 1.23 V, yet a practical water electrolyser typically runs at 1.8 to 2.0 V. A fresh battery rated at 1.5…
Explore lesson ChemistryCollectionOxidation and Reduction
Study Oxidation and Reduction with 50 free lessons, worked examples, and answered practice questions.
Explore lesson ChemistryLessonOxidation and Reduction in Cells
The words anode and cathode name electrode functions, not permanent signs. Oxidation happens at the anode and reduction at the cathode in both galvanic and electrolytic cells. To…
Explore lesson ChemistryLessonOxidation and Reduction Unit Review
This unit began with oxygen gain and loss, then broadened to electron transfer and formal oxidation-number changes. The shared principle is paired change: one species is oxidised…
Explore lesson ChemistryLessonOxidation as Addition of Oxygen
Many familiar oxidation reactions visibly add oxygen to a material. A metal becomes an oxide, or a fuel reacts with oxygen in air. This historical observation gave oxidation its…
Explore lesson ChemistryLessonOxidation Levels and Carbonyl Interconversions
Organic reactions change both the bonds around carbon and the functional-group label we assign. An alcohol can be oxidised to an aldehyde or ketone, and an aldehyde can be…
Explore lesson ChemistryLessonOxidation Levels of Carbon
In an organic conversion, oxidation and reduction describe how electron ownership around carbon changes. A quick practical guide is to count bonds from the carbon of interest to…
Explore lesson ChemistryLessonOxidation Number and Monatomic Ion Charge
For a monatomic ion, oxidation number equals the ion's charge. Fe³⁺ has +3, Cu⁺ has +1 and Cl⁻ has −1. This simple rule connects the earlier electron-counting half-reactions to…
Explore lesson ChemistryLessonOxidation Number Is Not Always Ionic Charge
Oxidation number and ionic charge match for a monatomic ion, but they are not the same concept in every species. Carbon has oxidation number +4 in neutral CO₂, and sulfur has +6…
Explore lesson ChemistryLessonOxidation Number of an Element
An atom in a free elemental substance has oxidation number zero. This rule applies whether the substance consists of single atoms, metal lattices, diatomic molecules or larger…
Explore lesson ChemistryLessonOxidation Number Rules
Oxidation numbers turn many redox reactions into a clear accounting problem. They are formal values assigned to atoms by rules, and changes in those values identify oxidation or…
Explore lesson ChemistryLessonOxidation Numbers as a Tracking Tool
Oxidation numbers let us compare the same element before and after a reaction even when formulas contain covalent bonds rather than free ions. They are formal bookkeeping…
Explore lesson ChemistryLessonOxidation Numbers in Ions
A polyatomic ion can carry an overall charge while its atoms have different assigned oxidation numbers. Sulfate is SO₄²⁻: its charge is −2, but sulfur is not −2. The oxygen atoms…
Explore lesson ChemistryLessonOxidation of Aldehydes and Ketones
Aldehydes commonly oxidise to carboxylic acids, whereas ketones do not usually undergo an analogous simple oxidation under mild conditions. The distinction is useful in both…
Explore lesson ChemistryLessonOxidation of Metals and Reduction of Ions
Metal displacement is an electron-transfer exchange. The solid metal that dissolves is oxidized, while the dissolved metal ion that becomes solid is reduced. Half-equations make…
Explore lesson ChemistryLessonOxidation of Primary Alcohols
A primary alcohol can be oxidized first to an aldehyde and, under stronger or prolonged oxidizing conditions, further to a carboxylic acid. The carbon skeleton usually remains…
Explore lesson ChemistryLessonOxidation of Secondary and Tertiary Alcohols
Secondary alcohols commonly oxidize to ketones, while tertiary alcohols resist the same simple carbonyl-forming transformation. The reason lies at the OH-bearing carbon: a…
Explore lesson ChemistryLessonOxidation States and d-Electron Counts
Formal oxidation state and d count organise metal chemistry even when bonds are strongly covalent. They help track oxidative addition, reduction and coordination changes across a…
Explore lesson ChemistryLessonOxidation-Number Balancing Method
The half-reaction method tracks explicit electrons. An alternative starts by finding the total increase and decrease in oxidation numbers. Choose coefficients that make those…
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