Structure of the Atom

60 lessons, pages 901–960.

  1. Atomic Models as Scientific Explanations — Using evidence to improve a model of the atom
  2. What Cathode Rays Established — Revisiting Thomson's evidence for a universal negative particle
  3. Electron Charge and Mass — Connecting charge-to-mass and oil-drop measurements
  4. Thomson's Model and Its Prediction — A diffuse positive charge tested by particle scattering
  5. Alpha Scattering: Evidence and Inference — Most particles pass through while a few deflect strongly
  6. Rutherford's Nuclear Atom — A compact positive nucleus and mostly empty atomic volume
  7. Comparing Nuclear and Atomic Scale — Orders of magnitude for radii and why mass is concentrated
  8. Protons, Neutrons and Electrons Revisited — Charges, relative masses and locations in one model
  9. Atomic Number Defines an Element — Proton count and the identity of every atom
  10. Mass Number and Nucleon Counting — Adding protons and neutrons without confusing atomic mass
  11. Reading Nuclide Symbols — Solving for Z, A and neutron number from nuclear notation
  12. Particle Counts in Charged Ions — How electron loss or gain changes charge but not element
  13. Isotopes and Element Identity — Same protons, different neutrons and mass numbers
  14. Isobars and Isotones — Distinguishing equal mass number from equal neutron number
  15. Atomic Mass Unit and Carbon-12 — The reference scale for atomic and isotopic masses
  16. Mass Number Is Not Isotopic Mass — Whole-number nucleon count versus measured atomic mass
  17. Isotopic Abundance as a Fraction — Reading percentage and fractional abundances correctly
  18. Weighted Mean Atomic Mass — Calculating relative atomic mass from isotope data
  19. Finding an Unknown Isotope Abundance — Working backward from a weighted atomic mass
  20. Interpreting Mass Spectra — Mass-to-charge peaks and relative isotope abundances
  21. Isotope Uses and Limitations — Tracers, dating and what the isotope label does not tell us
  22. Why Rutherford's Model Was Incomplete — Atomic stability and discrete emission spectra
  23. Continuous and Line Spectra — Recognising evidence for quantised atomic energies
  24. Photons and Energy Changes — Relating light frequency to an atomic energy difference
  25. Bohr's Energy-Level Model — Allowed stationary levels in the hydrogen atom
  26. Absorption and Excitation — An electron taking in a photon to reach a higher level
  27. Emission and Relaxation — Photon release when an electron reaches a lower level
  28. Hydrogen Spectral Lines — Connecting several observed lines to level transitions
  29. Calculating Photon Wavelength — Using frequency, wavelength and energy relations
  30. What the Bohr Model Cannot Explain — Limits beyond one-electron atoms and fixed circular paths
  31. From Orbits to Orbitals — Probability regions rather than miniature planetary tracks
  32. Principal Shells and Subshells — Organising allowed electron states by n and subshell type
  33. Electron Capacity of a Shell — Using the 2n² maximum with its proper scope
  34. The s and p Subshells — Orbital counts and maximum electrons in the first twenty elements
  35. The Aufbau Filling Idea — Placing electrons into lower-energy available orbitals first
  36. Pauli Exclusion in Orbital Boxes — Two opposite-spin electrons at most in one orbital
  37. Hund's Rule for p Orbitals — Single occupation before electron pairing in equal-energy orbitals
  38. Drawing Orbital Box Diagrams — Combining filling order, Pauli exclusion and Hund's rule
  39. Writing Spectroscopic Configurations — Notation such as 1s² 2s² 2p⁶ for occupied subshells
  40. Hydrogen to Beryllium Configurations — Building the first four atoms one electron at a time
  41. Boron to Neon Configurations — Filling the second-shell p orbitals
  42. Sodium to Argon Configurations — Third-shell s and p filling and period-three patterns
  43. Potassium and Calcium Configurations — Why 4s fills before 3d in these neutral atoms
  44. Shell Notation and Subshell Notation — Translating arrangements such as 2,8,1 into orbital notation
  45. Valence Electrons and Outer Shells — Identifying electrons involved in common bonding patterns
  46. Configurations of Simple Cations — Removing electrons from neutral atoms to form positive ions
  47. Configurations of Simple Anions — Adding electrons to form common negative ions
  48. Isoelectronic Atoms and Ions — Different species with the same electron count
  49. Atomic Structure and Periodic Position — Inferring period and main-group pattern from configuration
  50. Electron Arrangement and Ion Formation — Explaining common charges with valence-electron patterns
  51. Ions and Their Sizes — Why a cation is often smaller and an anion larger than its atom
  52. Nuclear Charge and Electron Attraction — Connecting proton number to attraction without ignoring shielding
  53. Why Isotopes React Similarly — Shared electron arrangements and possible isotope effects
  54. Radioactive Isotopes in an Atomic Model — Separating nuclear instability from ordinary electron chemistry
  55. Limits of the Octet Shortcut — Useful first predictions and cases needing a deeper model
  56. Comparing Historical Atomic Models — What each model explained and what evidence replaced it
  57. Reading Atomic Data Tables — Linking symbol, Z, relative mass, isotope and ion charge
  58. Solving Mixed Particle-Count Problems — Combining isotope notation, ion charge and electron arrangement
  59. Atomic Evidence and Model Choice — Choosing the simplest model that explains an observation
  60. Structure of the Atom: Unit Review — Models, isotopes, spectra and electron configurations together