⚛️ Atomic Structure & Periodicity
115 chemistry topics in Atomic Structure & Periodicity, from beginner to intermediate to advanced level. Each topic has a clear explanation, a worked example, frequently asked questions and an interactive lesson.
Beginner topics in Atomic Structure & Periodicity (54)
- MatterAnything that has mass and occupies space; it exists mainly as solids, liquids and gases.
- AtomThe smallest unit of an element that retains the element's chemical identity, made of…
- ElementA pure substance made of atoms with the same atomic number; it cannot be broken down…
- CompoundA pure substance of two or more elements chemically combined in a fixed ratio.
- MixtureA physical combination of substances in which each keeps its own properties and can be…
- Pure SubstanceMatter with a fixed composition and distinct properties, either an element or a compound.
- Physical ChangeA change in form or state, such as melting or dissolving, that does not alter chemical…
- Chemical ChangeA process in which substances are transformed into new substances with different…
- Law of Conservation of MassMass is neither created nor destroyed in a chemical reaction, so total mass of reactants…
- Law of Definite ProportionsA given compound always contains the same elements in the same mass proportions…
- Dalton's Atomic TheoryProposes that matter consists of indivisible atoms, atoms of an element are identical,…
- ElectronA negatively charged subatomic particle with a mass about 1/1836 of a proton, discovered…
- ProtonA positively charged particle in the nucleus whose count defines the atomic number of an…
- NeutronA neutral nuclear particle with mass slightly greater than a proton, discovered by…
- Thomson's Plum Pudding ModelAn early model picturing electrons embedded in a diffuse positively charged sphere.
- Rutherford's Gold Foil ExperimentAlpha particles mostly passed through gold foil but some deflected sharply, revealing a…
- Nuclear Atom ModelAtom has a tiny dense nucleus holding nearly all the mass, surrounded by electrons in…
- Atomic NumberThe number of protons in an atom's nucleus, symbol Z, which determines the element.
- Mass NumberThe total count of protons and neutrons in a nucleus, symbol A.
- IsotopesAtoms of the same element with the same proton number but different neutron numbers.
- Relative Atomic MassThe weighted average mass of an element's isotopes relative to one twelfth of a carbon-12…
- Atomic Mass UnitA mass unit equal to one twelfth of the mass of a carbon-12 atom, about 1.66 x 10^-27 kg.
- MoleThe amount of substance containing exactly 6.022 x 10^23 elementary entities.
- Avogadro's NumberThe number of particles in one mole, 6.022 x 10^23 per mole.
- Molar MassThe mass of one mole of a substance in grams, numerically equal to its relative formula…
- Cathode RaysStreams of electrons observed in discharge tubes, deflected by electric and magnetic…
- Wavelength and FrequencyWavelength is the distance between wave crests; frequency is waves per second; their…
- Electromagnetic SpectrumThe range of radiation from radio waves to gamma rays, ordered by wavelength and energy.
- Atomic Emission SpectraLight emitted by excited atoms appears as discrete bright lines characteristic of each…
- Atomic OrbitalA region of space around the nucleus where the probability of finding an electron is high.
- Principal Quantum NumberThe number n that defines the shell and overall size and energy of an orbital.
- Shapes of s and p Orbitalss orbitals are spherical while p orbitals are dumbbell-shaped with a nodal plane through…
- Electron Shells and SubshellsShells are labelled by n and contain subshells s, p, d and f with 1, 3, 5 and 7 orbitals…
- Aufbau PrincipleElectrons fill orbitals in order of increasing energy, starting from the lowest available.
- Pauli Exclusion PrincipleNo two electrons in an atom can have the same set of four quantum numbers, so an orbital…
- Hund's RuleElectrons occupy degenerate orbitals singly with parallel spins before pairing up.
- Electron ConfigurationThe distribution of an atom's electrons among its orbitals, such as 1s2 2s2 2p6 for neon.
- Noble Gas ShorthandCore electrons are written as the preceding noble gas symbol in brackets followed by…
- Valence ElectronsElectrons in the outermost shell that take part in bonding and determine chemical…
- Core ElectronsInner-shell electrons that do not normally take part in chemical bonding.
- Periodic LawProperties of elements are periodic functions of their atomic numbers.
- Mendeleev's Periodic TableAn arrangement by atomic mass that predicted undiscovered elements by leaving gaps.
- Modern Periodic TableElements arranged by increasing atomic number into 18 groups and 7 periods.
- Periods and GroupsPeriods are horizontal rows indicating the outer shell; groups are vertical columns of…
- s-Block ElementsGroups 1 and 2 elements whose last electron enters an s orbital, comprising alkali and…
- p-Block ElementsGroups 13 to 18 elements whose last electron enters a p orbital, including nonmetals,…
- d-Block ElementsTransition elements whose last electron enters a d orbital, in groups 3 to 12.
- f-Block ElementsLanthanides and actinides in which the 4f or 5f subshell is being filled.
- Metals Nonmetals and MetalloidsMetals are lustrous conductors, nonmetals are poor conductors, and metalloids show…
- Atomic RadiusHalf the distance between nuclei of bonded identical atoms; it decreases across a period…
- Ionization EnergyThe energy needed to remove the outermost electron from a gaseous atom, generally…
- ElectronegativityAn atom's tendency to attract bonding electrons, highest for fluorine.
- Metallic CharacterThe tendency to lose electrons, increasing down a group and decreasing across a period.
- Hydrogen PositionHydrogen has one electron like alkali metals yet forms diatomic nonmetallic gas, so it…
Intermediate topics in Atomic Structure & Periodicity (45)
- Law of Multiple ProportionsWhen two elements form more than one compound, masses of one combining with a fixed mass…
- IsobarsAtoms of different elements that have the same mass number but different atomic numbers.
- IsotonesNuclides having the same number of neutrons but different numbers of protons.
- Mass SpectrometryA technique that ionizes atoms or molecules and separates them by mass-to-charge ratio to…
- Millikan's Oil Drop ExperimentMeasured the elementary charge of the electron, 1.602 x 10^-19 coulomb, by balancing…
- Electromagnetic RadiationEnergy that travels as oscillating electric and magnetic fields at the speed of light in…
- Black Body RadiationRadiation from an ideal absorber whose spectrum could only be explained by Planck's idea…
- Planck's Quantum TheoryEnergy is emitted or absorbed in discrete packets called quanta, with E equal to h times…
- Photoelectric EffectElectrons are ejected from a metal surface when light above a threshold frequency strikes…
- Threshold FrequencyThe minimum light frequency needed to eject electrons from a metal surface.
- Work FunctionThe minimum energy required to remove an electron from a metal's surface.
- PhotonA quantum of light carrying energy E equals h times frequency.
- Atomic Absorption SpectraDark lines in a continuous spectrum where an element absorbs the same wavelengths it…
- Hydrogen Spectrum SeriesLyman, Balmer, Paschen, Brackett and Pfund series arise when electrons fall to levels n=1…
- Rydberg EquationPredicts spectral line wavelengths of hydrogen from the initial and final principal…
- Bohr ModelElectrons orbit the nucleus in fixed circular orbits with quantized angular momentum and…
- Bohr Energy LevelsThe energy of the nth hydrogen level is -13.6 eV divided by n squared.
- Limitations of Bohr ModelIt fails for multi-electron atoms, cannot explain fine structure or the Zeeman effect,…
- de Broglie HypothesisAll matter has wave character with wavelength equal to Planck's constant divided by…
- Heisenberg Uncertainty PrincipleIt is impossible to determine simultaneously the exact position and momentum of a…
- Azimuthal Quantum NumberThe number l, from 0 to n-1, defining the subshell and orbital shape.
- Magnetic Quantum NumberThe number m_l, from -l to +l, defining the orientation of an orbital in space.
- Spin Quantum NumberThe number m_s, either +1/2 or -1/2, describing the intrinsic spin of an electron.
- Shapes of d and f Orbitalsd orbitals are mostly cloverleaf shaped and f orbitals have more complex multi-lobed…
- Madelung RuleOrbitals fill in order of increasing n plus l, and for equal sums in order of increasing…
- Exceptional Configurations of Cr and CuChromium and copper adopt half-filled or fully filled d subshells for extra stability,…
- Effective Nuclear ChargeThe net positive charge felt by an electron after accounting for shielding by other…
- Shielding EffectInner electrons reduce the attraction between the nucleus and outer electrons.
- Ionic RadiusThe size of an ion; cations are smaller and anions larger than their parent atoms.
- Isoelectronic SpeciesAtoms and ions with the same number of electrons, whose size decreases as nuclear charge…
- Successive Ionization EnergiesEach further removal costs more energy, with a large jump when a core electron must be…
- Anomalies in Ionization EnergyDrops at Be to B and N to O arise from subshell shielding and electron-pair repulsion.
- Electron AffinityThe energy change when a gaseous atom gains an electron; halogens have the most negative…
- Pauling ScaleA relative electronegativity scale based on bond energies, with fluorine at 3.98.
- Diagonal RelationshipSimilarities between diagonal neighbours such as Li and Mg or Be and Al due to similar…
- Periodic Trends in Oxidation StateMaximum oxidation state generally equals group valence electrons across the main-group…
- Periodic Trends in OxidesOxides change from basic on the left of a period through amphoteric to acidic on the…
- RadioactivityThe spontaneous emission of particles or radiation from unstable nuclei.
- Alpha DecayEmission of a helium-4 nucleus, lowering atomic number by 2 and mass number by 4.
- Beta DecayA neutron changes into a proton emitting an electron and antineutrino, raising atomic…
- Gamma RadiationHigh-energy electromagnetic photons emitted by excited nuclei without changing mass or…
- Half-lifeThe time required for half of a radioactive sample to decay.
- Nuclear FissionA heavy nucleus splits into lighter nuclei releasing large energy, as in nuclear reactors.
- Nuclear FusionLight nuclei merge into heavier ones releasing energy, powering the stars.
- Radiocarbon DatingEstimates age of organic remains from the remaining fraction of carbon-14, half-life 5730…
Advanced topics in Atomic Structure & Periodicity (16)
- Wave FunctionA mathematical function psi whose square gives the probability density of finding an…
- Schrodinger EquationThe fundamental equation of quantum mechanics whose solutions give electron wave…
- Radial and Angular NodesRadial nodes are spherical surfaces of zero electron density, numbering n-l-1; angular…
- Slater's RulesAn empirical method for estimating shielding constants and effective nuclear charge of…
- Penetration of OrbitalsThe ability of an orbital to approach the nucleus; s penetrates more than p, d and f in…
- Mulliken ElectronegativityDefined as the average of ionization energy and electron affinity of an atom.
- Inert Pair EffectReluctance of heavy p-block elements to use their s electrons in bonding, favouring lower…
- Lanthanide ContractionThe gradual decrease in size across lanthanides due to poor shielding by 4f electrons.
- Quark Structure of NucleonsProtons and neutrons are composed of up and down quarks held together by the strong force.
- Nuclear Binding EnergyThe energy released when nucleons form a nucleus, equivalent to the mass defect times c…
- Mass DefectThe difference between the mass of a nucleus and the sum of its separate nucleons.
- Magic NumbersProton or neutron counts such as 2, 8, 20, 28, 50, 82 and 126 that give especially stable…
- Island of StabilityA predicted region of superheavy nuclei with relatively long half-lives.
- Zeeman EffectSplitting of spectral lines when atoms are placed in a magnetic field.
- Stark EffectSplitting of spectral lines in an electric field.
- Term SymbolsNotation describing total orbital angular momentum, spin and total angular momentum of an…
Frequently asked questions about Atomic Structure & Periodicity
How many topics are in Atomic Structure & Periodicity?
Atomic Structure & Periodicity has 115 topics, from beginner to intermediate to advanced level.
Where should I start in Atomic Structure & Periodicity?
Start with Matter at the beginner level, then work through the topics in order.
Does every topic have an explanation and an example?
Yes. Each topic page has an in-depth explanation, a worked example, FAQs and links to related topics.