Periodic Classification and Trends

60 lessons, pages 961–1020.

  1. Periodic Law as a Predictive Pattern — Recurring properties when elements are ordered by atomic number
  2. Evidence Behind Modern Atomic-Number Order — Why proton number replaced relative atomic mass as the organising principle
  3. Mendeleev's Predictions Revisited — Gaps, predicted properties and the limits of mass-based ordering
  4. Reading Periodic Table Data Precisely — Element symbol, atomic number, average mass and category labels
  5. Periods and Occupied Electron Shells — Using neutral ground-state configurations to identify a row
  6. Main Groups and Valence Patterns — Repeated outer s and p occupancy down a column
  7. Blocks and the Filling of Subshells — Connecting s, p, d and f regions to configuration notation
  8. Why the First Period Is Short — Only the 1s orbital is available in the first shell
  9. Second- and Third-Period Lengths — Eight places each from outer s and p filling
  10. Fourth-Period Ordering and the d Block — How 4s and 3d filling make the row longer
  11. Hydrogen and Helium as Special Cases — Electron-pattern placement versus distinct chemical behaviour
  12. Families and Similar Chemical Properties — What a shared valence pattern predicts and what it cannot
  13. Cation and Anion Patterns by Group — Common main-group charges and their limitations
  14. Electron Shielding Across the Table — Inner electrons and the effective pull on outer electrons
  15. Effective Nuclear Charge Across a Period — More protons with similar inner-shell shielding
  16. Distance and Shielding Down a Group — Why added shells matter despite increasing nuclear charge
  17. What Atomic Radius Measures — Covalent, metallic and van der Waals conventions
  18. Atomic Radius Across a Period — General contraction and exceptions to a simple arrow
  19. Atomic Radius Down a Group — Larger occupied shells and greater shielding
  20. Comparing Radius Data Fairly — Matching radius definitions before using numerical values
  21. Cations, Anions and Parent-Atom Size — Electron loss, electron gain and changes in effective radius
  22. Isoelectronic Radius Ordering — Using proton count to rank ions with equal electron numbers
  23. First Ionisation Energy Defined — Energy needed to remove an electron from a gaseous atom
  24. Successive Ionisation Energies — Why later electron removals cost more and show large jumps
  25. Ionisation Energy Across a Period — Increasing attraction with subshell and pairing exceptions
  26. Ionisation Energy Down a Group — Shielding and distance outweighing greater proton number
  27. Explaining Ionisation Exceptions — Comparing s versus p removal and paired-electron effects
  28. Electron Affinity and Electron Gain — Energy changes when gaseous atoms accept electrons
  29. Electron-Affinity Trends with Caution — Why a single direction arrow hides real exceptions
  30. Electronegativity in a Bond — Relative attraction for shared bonding electrons
  31. Electronegativity Across a Period — Increasing effective attraction in many main-group bonds
  32. Electronegativity Down a Group — More distant valence electrons and weaker bond-electron attraction
  33. Keeping Three Attraction Trends Distinct — Ionisation energy, electron affinity and electronegativity compared
  34. Metallic Character Across a Period — From easier electron loss toward non-metal patterns
  35. Metallic Character Down a Group — Why larger atoms commonly behave more metallic
  36. Non-Metallic Character and Position — Broad opposite trend and exceptions in chemistry
  37. Oxide Behaviour Across Period Three — Basic, amphoteric and acidic oxide patterns
  38. Alkali Metal Trends Explained — Size, ionisation energy and common reactivity down group one
  39. Alkaline Earth Metal Trends — Two valence electrons and changing behaviour down group two
  40. Halogen Trends Explained — Size, physical state and oxidising behaviour down group seventeen
  41. Noble Gases and Filled Outer Shells — Low ordinary reactivity without claiming absolute inertness
  42. Transition Elements in Periodic Classification — d-block patterns and variable oxidation states
  43. Lanthanides and Actinides in the Table — f-block placement and why the rows are displayed below
  44. Metalloids and Boundary Behaviour — Mixed properties near the conventional metal–non-metal divide
  45. Periodic Trends Versus Individual Exceptions — Using qualified predictions rather than universal arrows
  46. Predicting Simple Compounds from Groups — Valence patterns, ion charges and formula balance
  47. Predicting Reaction Behaviour from Position — What periodic placement suggests and what conditions decide
  48. Comparing Adjacent Elements — Controlling period and group when explaining differences
  49. Comparing Elements in One Group — Separating shared valence chemistry from changing size
  50. Period Three as a Trend Case Study — Linking configurations, sizes and oxide behaviour from sodium to argon
  51. Reading Trend Graphs and Tables — Axes, units, missing values and exceptional points
  52. Finding an Unknown Element from Clues — Using Z, configuration, group and trend evidence together
  53. Explaining a Trend with Evidence — Writing claim, electron-structure reason and qualification
  54. Common Periodic-Trend Traps — Charge, radius definitions and overgeneralised arrows
  55. Periodic Classification and Materials — How position guides choices of metals, semiconductors and gases
  56. Periodic Data and Model Limits — Distinguishing a measured property from a simple explanation
  57. Mixed Radius and Ionisation Problems — Comparing species while controlling shell and electron count
  58. Mixed Group and Bonding Problems — Combining position, valence electrons and plausible ion formulas
  59. Evaluating Periodic Predictions — Testing a proposed trend against exceptions and data
  60. Periodic Classification and Trends: Unit Review — Modern law, electron structure, radius and metallic character together