105 articles
Atomic Structure
Protons, neutrons, electrons, orbitals and electron configurations — what atoms are made of and how their electrons are arranged.
The Atomic Mass Unit (Dalton): Definition and Uses
What the atomic mass unit (u or Da) is, why it's defined as one-twelfth of a carbon-12 atom, its value in kilograms, how it connects to the mole and molar mass, why protons and neutrons aren't exactly 1 u, history of hydrogen, oxygen and carbon scales, and uses in chemistry, biochemistry and mass spectrometry.
Models of the Atom: Practice Questions
Fifteen practice questions on the history of atomic models, from Dalton and Thomson to Rutherford, Bohr, Chadwick and the quantum model, with a full answer key and a summary timeline.
Atomic Number: Why the Proton Count Defines an Element
What atomic number is, why the number of protons (and not electrons or neutrons) defines an element, how Henry Moseley discovered it with X-rays, how it orders the periodic table, what changes it in nuclear reactions, and worked examples of using it.
Atomic Structure Glossary: 60 Key Terms Defined
Sixty essential atomic-structure terms, from alpha particle to Zeeman effect, each defined in plain English with an example and a link to a full explanation. A handy revision reference for students.
10 Misconceptions About Atoms (and What's Actually True)
Ten common misconceptions about atoms corrected clearly: that atoms are solid balls, that electrons orbit like planets, that atoms of a substance share its properties, that atoms are alive, that isotopes are radioactive, that bigger atoms have more electron shells in every case, and more, with the evidence behind each correction.
Atomic Structure Practice Questions: Protons, Neutrons and Electrons
Twenty-five beginner-friendly atomic structure practice questions with full answers: counting protons, neutrons and electrons in atoms, isotopes and ions, completing tables, identifying elements, relative atomic mass, electron shell arrangements and short-answer questions on atomic models.
Atomic Structure Study Guide: Everything for Your Exam
A complete revision guide to atomic structure: subatomic particles, atomic and mass numbers, isotopes and relative atomic mass, the history of atomic models, electron shells and configurations, ions, spectra and ionisation energy, with checkpoint questions, answers and a one-week revision plan linking to every topic.
Atoms vs Molecules vs Compounds vs Elements
Clear definitions and a side-by-side comparison of atoms, elements, molecules, compounds and mixtures, with examples, a decision flowchart, tricky cases like O₂ and NaCl, and quick practice questions.
The Bohr Model: What It Got Right and Where It Fails
Niels Bohr's 1913 model of the atom explained: the problem with Rutherford's atom, Bohr's three postulates, fixed energy levels, how it explained hydrogen's line spectrum, what it got right, why it fails for other atoms and chemical bonding, and why it's still taught today.
The Cathode Ray Tube Experiment Explained
A beginner's guide to the cathode ray tube: how the tube is built, what happens when high voltage is applied, the observations that showed cathode rays are negatively charged particles, how electric and magnetic fields deflect the beam, how Thomson used it to discover the electron, and how the same technology powered old TVs and oscilloscopes.
Dalton's Atomic Theory: Five Ideas That Launched Modern Chemistry
The story of John Dalton, the Quaker schoolteacher from Manchester whose atomic theory of 1803–1808 turned atoms from philosophy into science: the laws that inspired it, his five key ideas, his symbols and early atomic weights, what he got wrong, and why his theory still shapes chemistry.
Democritus and the Ancient Greek Idea of the Atom
Twenty-four centuries ago, Leucippus and Democritus argued that everything is made of tiny, uncuttable pieces moving through empty space. Here is how the idea began, why it was rejected, and how it survived.
Electron Shells: The 2, 8, 8 Rule and Where It Comes From
A beginner's guide to electron shells: how to fill shells for the first 20 elements with the 2, 8, 8 pattern, drawing shell diagrams, why the third shell 'pauses' at 8, how shells explain groups and periods, valence electrons and reactivity, and when the simple shell model stops working.
Electron Shell Diagrams Practice (First 20 Elements)
Practice drawing and interpreting electron shell diagrams for the first 20 elements: 2,8,8,2 arrangements, ions, groups and periods, with a complete answer key and a reference table.
Fireworks and Electron Transitions: The Physics Behind the Colours
How fireworks produce their colours: fuel and oxidiser chemistry, heat exciting electrons, the metals behind red, orange, yellow, green, blue and purple, why many colours come from small molecules like SrCl and BaCl, why blue is hardest, incandescence vs luminescence, and modern safer and greener formulas.
Emission Spectra with a Spectroscope: A Classroom Investigation
A school-lab-safe investigation of emission spectra: using a hand-held spectroscope with gas discharge tubes, flame tests and everyday lights to see line spectra, record observations and link them to electron energy levels.
How Many Atoms Are in the Observable Universe?
The famous answer is about 10⁸⁰ atoms. Here is how scientists estimate it, step by step, using stars and galaxies and then cosmic density, plus how that number compares with atoms in the Earth, your body and a drop of water.
How Small Is an Atom? Scale, Size and Mind-Bending Comparisons
Just how tiny atoms are, with real numbers and comparisons: atomic radii in picometres, how many atoms fit across a hair, the mass of a single atom, the size of the nucleus, the number of atoms in a drop of water or a human body, and how scientists measure something so small.
How to Read and Write Isotope Notation (AZX and Element-Mass Forms)
A step-by-step guide to isotope notation: the AZX nuclide symbol, element-mass names like carbon-14, writing ions with charges, notation for particles in nuclear equations, balancing mass and atomic numbers, and common mistakes, with practice questions and answers.
Isotopes Practice Questions with Answers
Fourteen isotope practice questions, from counting protons and neutrons to calculating relative atomic mass and finding abundances, with a full worked answer key for every question.
Lewis Dot Symbols for Atoms and Ions
A step-by-step guide to drawing Lewis dot symbols for atoms and ions: counting valence electrons, placing the dots, showing ionic charges, and using the symbols to predict simple ionic and covalent formulas.
Mass Number: How to Calculate Neutrons, Protons and Electrons
Worked examples on mass number: what A and Z mean, how to find the numbers of protons, neutrons and electrons in atoms, isotopes and ions, reading nuclide notation, why mass number is a whole number but relative atomic mass isn't, and common exam traps.
Noble Gas Shorthand: Writing Electron Configurations the Fast Way
How to write electron configurations in noble gas (condensed) notation: choosing the right core, step-by-step method, worked examples from sodium to lead, using the periodic table as a map, ions, why the core is chemically unimportant, ordering conventions, and practice questions with answers.
The Octet Rule: Why Atoms "Want" Eight Electrons (and When They Don't)
What the octet rule says, where it came from (Lewis and Langmuir), why eight electrons correspond to filled s and p subshells, how it predicts ionic charges and covalent bonding, worked Lewis-structure examples, the duet rule for hydrogen, why 'wanting' is the wrong language, and a preview of the main exceptions.
How to Predict the Charge of an Ion from the Periodic Table
A step-by-step method for predicting ion charges from group numbers: metals in groups 1, 2 and 13, non-metals in groups 15, 16 and 17, noble gases, why hydrogen is special, transition metals with variable charges and Roman numerals, common polyatomic ions, worked examples writing formulas, and exceptions.
Rutherford's Gold Foil Experiment: How the Nucleus Was Found
The story of the Geiger–Marsden experiment in Manchester: why alpha particles were fired at gold foil, what Thomson's model predicted, the shock of particles bouncing back, Rutherford's 1911 nuclear model, how the results were analysed, what the model couldn't explain, and why this experiment still matters.
Teaching the History of Atomic Models
A teacher's guide to the history of atomic models: a lesson sequence built around evidence, the Rutherford scattering simulation, black-box activities, misconceptions to expect and questions that test scientific reasoning.
Teaching Atomic Structure: A Lesson Plan and Activities
A practical guide for teachers on teaching atomic structure: a five-lesson sequence, hands-on activities (the mystery box, scale models, modelling the gold foil experiment, isotope 'beans'), questioning strategies, common misconceptions to target, assessment ideas and differentiation.
Teaching Isotopes and Relative Atomic Mass
A teacher's guide to isotopes and relative atomic mass: a two-lesson plan, the 'bag of sweets' weighted-average activity, mass spectra, common student errors and a graded question set with answers.
Thomson's Plum Pudding Model and the Discovery of the Electron
The story of J.J. Thomson at the Cavendish Laboratory: the cathode ray mystery, the 1897 experiments that revealed the electron and its charge-to-mass ratio, the 1904 plum pudding model of the atom, why it made sense at the time, how Rutherford's experiment overturned it, and Thomson's lasting legacy.