105 articles
Atomic Structure
Protons, neutrons, electrons, orbitals and electron configurations — what atoms are made of and how their electrons are arranged.
Ionic Radius: Why Cations Shrink and Anions Grow
What ionic radius means and how it's measured, why positive ions are smaller than their atoms and negative ions larger, trends down groups and across periods, isoelectronic series, how charge and coordination number affect size, worked ranking examples, and why ionic size matters for lattice energy, solubility and biology.
How Atoms Become Ions: Gaining and Losing Electrons
The energy story behind ion formation: ionisation energy for making cations, electron affinity for making anions, why forming isolated ions usually costs energy, how lattice energy and hydration pay the bill, a Born–Haber style walk-through for sodium chloride, and ions formed in flames, solutions, batteries and the atmosphere.
Isoelectronic Species: Same Electrons, Different Sizes
What isoelectronic means, how to spot isoelectronic atoms, ions and molecules, why radius decreases as nuclear charge increases across an isoelectronic series, trends in ionisation energy, isoelectronic molecules such as N₂, CO and CN⁻, and exam-style ranking questions with answers.
Isotopes vs Isobars vs Isotones
Isotopes share protons, isobars share mass number, isotones share neutrons. A side-by-side comparison with examples, a memory trick, where each idea matters in nuclear chemistry, and practice questions.
Millikan's Oil Drop Experiment: Measuring the Charge of an Electron
The story and physics of Robert Millikan's oil drop experiment (1909–1913): why the electron's charge mattered, the apparatus, balancing electric and gravitational forces, how the whole-number pattern revealed the elementary charge, a worked example, the controversy over his data, and the experiment's legacy.
How to Draw Orbital Box Diagrams Step by Step
A step-by-step method for drawing orbital box (arrows-in-boxes) diagrams: setting out boxes for each subshell, applying the Aufbau principle, Pauli exclusion and Hund's rule, worked examples from hydrogen to iron, ions, noble gas shorthand, counting unpaired electrons, and common mistakes.
Orbital Box Diagram Practice Questions
Twelve orbital box diagram questions with full answers: filling boxes with Hund's rule and the Pauli principle, counting unpaired electrons, spotting errors, ions, and the chromium and copper exceptions.
Paramagnetic vs Diamagnetic: Predicting Magnetism from Electrons
The difference between paramagnetic and diamagnetic substances, how unpaired electrons create magnetism, predicting magnetic behaviour from electron configurations of atoms, ions and molecules, ferromagnetism, the liquid oxygen demonstration, measuring magnetism, and practice questions.
The Pauli Exclusion Principle in Plain Language
What the Pauli exclusion principle says, why no two electrons in an atom can share all four quantum numbers, why each orbital holds only two electrons with opposite spins, how it produces shell capacities, the periodic table and the solidity of matter, and its role in white dwarfs and neutron stars.
The Photoelectric Effect: The Experiment That Proved Light Comes in Packets
What the photoelectric effect is, the puzzling observations that classical wave theory couldn't explain, Einstein's 1905 photon explanation, threshold frequency and work function, why intensity changes the number but not the energy of electrons, Millikan's confirmation, and everyday uses from solar cells to night-vision.
Photons and Energy Levels: Why Atoms Emit Specific Colours
How quantised energy levels and photons explain the colours of flames, fireworks, neon signs and street lamps: ground and excited states, the relationship E = hf, why each element has its own colours, fluorescence and phosphorescence, lasers, and why molecules and solids give broader colours.
The Quantum Mechanical Model of the Atom
An overview of the modern quantum mechanical model of the atom: how it grew out of the Bohr model, its key ideas (wave behaviour, quantised energy, orbitals, probability, four quantum numbers), how it explains the periodic table and bonding, what it predicts that earlier models couldn't, and how to describe it in exams.
Quantum Numbers Practice Questions (with Answer Key)
Twenty-four graded practice questions on quantum numbers: allowed values of n, l, mₗ and mₛ, naming orbitals, counting orbitals and electrons, spotting impossible sets, assigning quantum numbers to electrons, nodes and exam-style explanations, with a full answer key and explanations.
Quarks, Gluons and What Protons Are Made Of
A clear introduction to the particles inside protons and neutrons: up and down quarks and their fractional charges, gluons and the strong force, why quarks are never found alone, where the proton's mass really comes from, how deep inelastic scattering revealed quarks, and why chemists can mostly ignore them.
Calculating Relative Atomic Mass from Isotope Abundances
Worked examples for calculating relative atomic mass from isotope masses and percentage abundances, including chlorine, copper, magnesium and boron, data from mass spectra, using exact isotopic masses, three-isotope problems, and why the periodic table values aren't whole numbers.
Shells vs Subshells vs Orbitals: Untangling the Terminology
A clear comparison of electron shells, subshells and orbitals: what each term means, how they nest inside each other, how many electrons each holds, how they relate to quantum numbers and the periodic table, and a worked example taking one atom through all three levels of description.
Electron Spin: What the Spin Quantum Number Really Means
What electron spin is and isn't: the Stern–Gerlach experiment, the values +½ and −½, why spin is an intrinsic quantum property rather than literal rotation, its role in the Pauli principle, Hund's rule and magnetism, spin pairing in bonds, and applications in NMR, MRI, ESR and spintronics.
How to Interpret Successive Ionization Energy Graphs
A step-by-step guide to reading successive ionisation energy data and graphs: why each ionisation energy is larger than the last, how big jumps reveal the group and the number of outer electrons, using log graphs to see shells and subshells, worked examples for sodium, aluminium, silicon and an unknown element, and exam tips.
Teaching Electron Configuration Without the Confusion
A teacher's guide to electron configuration: a three-lesson sequence from shells to orbitals, the misconceptions students bring, hands-on activities, how to handle 4s and 3d, and a bank of check questions.
How to Count Unpaired Electrons in Atoms and Ions
A step-by-step method for counting unpaired electrons: from the electron configuration to the partly filled subshell, quick rules for p, d and f subshells, a lookup table for d¹ to d¹⁰, worked examples for main-group atoms, transition metal ions and lanthanides, and practice questions with answers.
Wave-Particle Duality: Are Electrons Waves or Particles?
An intermediate guide to wave-particle duality: evidence that light behaves as a wave and as particles, de Broglie's idea that matter has a wavelength, electron diffraction, the double-slit experiment with single electrons, why duality explains quantised energy levels, and what it means for chemistry.
Wavelength, Frequency and Photon Energy Calculations
Worked examples connecting wavelength, frequency and photon energy with c = fλ and E = hf: converting nm, pm, MHz and eV, energy per mole of photons, identifying spectral regions, comparing photon energy with bond energies, number of photons from a laser, and common unit mistakes.
The s, p, d and f Blocks of the Periodic Table Explained
Why the periodic table is divided into s, p, d and f blocks, how block widths come from orbital capacities, how to read electron configurations straight off the table, and why the f-block sits underneath.
Electron Configuration Rules: Aufbau, Pauli and Hund Explained
The three rules that determine how electrons fill orbitals, the filling order and how to remember it, orbital box diagrams, noble-gas shorthand, and ions.
Atomic Spectra and Photon Energy Practice Problems
Thirteen atomic spectra problems with full worked solutions: photon energy, frequency and wavelength, the Rydberg equation, hydrogen energy levels, ionization energy, series limits, He⁺ and photon counting.
Bohr Model Calculations: Energy Levels, Radii and Transitions
Worked Bohr model calculations for hydrogen and one-electron ions: energy of each level, energy of transitions, wavelength and frequency of emitted photons, ionisation energy in J, eV and kJ/mol, orbit radii, scaling with Z² for He⁺ and Li²⁺, and common mistakes.
The de Broglie Wavelength with Worked Examples
Worked examples using λ = h/mv: wavelengths of electrons, protons, neutrons, atoms and everyday objects, electrons accelerated through a voltage, comparing with atomic spacings, finding speed from wavelength, why large objects show no wave behaviour, and the link to Bohr's orbits.
Effective Nuclear Charge and Shielding: The Engine Behind Periodic Trends
An advanced explanation of effective nuclear charge (Zeff) and shielding: why outer electrons feel less than the full nuclear charge, how penetration makes s electrons feel more, how Zeff changes across periods and down groups, and how it explains atomic radius, ionisation energy, electronegativity, the 4s–3d order and the lanthanide contraction.
The Heisenberg Uncertainty Principle for Chemistry Students
What the Heisenberg uncertainty principle says and doesn't say, the relation Δx·Δp ≥ h/4π, worked estimates for an electron in an atom and a football, why electrons can't have Bohr-style orbits, zero-point energy, why atoms don't collapse, the energy–time relation and spectral line widths, and common misconceptions.
Why Lanthanide Electron Configurations Are So Irregular
An advanced look at the lanthanides' electron configurations: the 4f and 5d competition, which elements have a 5d electron and which don't, why europium and ytterbium favour 4f⁷ and 4f¹⁴, why the +3 oxidation state dominates, the lanthanide contraction and its consequences, and how 4f electrons give lanthanides their special light and magnetism.