Classification of Elements and Periodicity

35 lessons, pages 1581–1615.

  1. Why Classify Chemical Elements? — Using repeating properties to organize a growing element list
  2. Early Patterns Before the Modern Table — Triads and octaves as useful but limited classifications
  3. Mendeleev's Periodic Classification — Mass ordering, gaps and testable predictions
  4. Atomic Number and the Modern Periodic Law — Why proton number replaces atomic mass as the ordering key
  5. Reading Groups and Periods — Vertical families, horizontal rows and repeating patterns
  6. Electron Configuration and Periodic Position — Connecting occupied shells and valence electrons to location
  7. The s, p, d and f Blocks — Classifying elements by the subshell being filled
  8. Valence Electrons Across Main Groups — Explaining family resemblance without overgeneralizing oxidation states
  9. Effective Nuclear Charge — Nuclear attraction experienced by an electron amid shielding
  10. Shielding and Penetration — Why inner electrons and orbital type affect attraction
  11. Defining Atomic Radius — Operational radius measures for atoms without hard boundaries
  12. Atomic Radius Across a Period — Increasing effective nuclear attraction at similar shell level
  13. Atomic Radius Down a Group — Added principal shells versus nuclear-charge increase
  14. Cation and Anion Sizes — Electron loss or gain and changes in ionic radius
  15. Isoelectronic Radius Comparisons — Ranking ions with equal electron counts by nuclear charge
  16. First Ionisation Enthalpy — Energy required to remove an electron from a gaseous atom
  17. Ionisation Enthalpy Across and Down — Broad trends from size, shielding and nuclear attraction
  18. Ionisation Enthalpy Exceptions — Subshell and electron-pair effects in familiar period anomalies
  19. Successive Ionisation Enthalpies — Large jumps as evidence of inner-shell removal
  20. Electron Gain Enthalpy — Energy change when a gaseous atom accepts an electron
  21. Electron Gain Trends and Exceptions — Halogens, noble gases and small-atom repulsion
  22. Electronegativity in Bonds — Relative attraction for shared bonding electrons
  23. Electronegativity Trends — Across-period and down-group patterns with scale cautions
  24. Metallic and Nonmetallic Character — Electron-loss tendency, bonding and broad table regions
  25. Periodicity of Valency and Oxidation States — Recurring outer-electron patterns and compound formulas
  26. Oxides Across a Period — Basic, amphoteric and acidic behavior as a broad pattern
  27. Hydrides Across the Periodic Table — Ionic, covalent and interstitial descriptions with limits
  28. The Special Behavior of First-Row Elements — Small size, high charge density and bonding differences
  29. Diagonal Relationships — Selected similarities between adjacent-period elements
  30. Group One and Group Two Patterns — Comparing common s-block trends without treating members as identical
  31. Groups Seventeen and Eighteen — Halogen reactivity and noble-gas stability as patterns
  32. Transition and Inner-Transition Placement — Locating d- and f-block series on the long-form table
  33. Predicting an Unfamiliar Element — Using position and configuration to make qualified predictions
  34. Interpreting Periodic Trend Data — Graphs, units and exceptions in measured element properties
  35. Classification and Periodicity: Unit Review — Connecting atomic structure, radii, energies and chemical character