chem

Scientist

Contribution

Lavoisier

Listed known elements (late 1700s)

Newlands

Law of Octaves → properties repeat every 8

Meyer

Atomic mass ↔ properties

Mendeleev

Predicted undiscovered elements, periodic table by atomic mass

Moseley

Atomic number → modern periodic table; solved inconsistencies

2. Modern Periodic Table Structure

  • Rows: Periods → principal energy level

  • Columns: Groups/Families → similar chemical properties

  • Blocks:

    • s-block: Groups 1–2 + He, 1–2 valence electrons

    • p-block: Groups 13–18, valence electrons = group # – 10

    • d-block: Groups 3–12, transition metals

    • f-block: Lanthanides & Actinides, inner transition metals

  • Element Types:

    • Metals: shiny, malleable, ductile, good conductors

    • Nonmetals: dull, poor conductors, gases/liquids

    • Metalloids: mix of metal & nonmetal properties

  • Special Groups:

    • Alkali metals (1): very reactive, lose 1 e⁻

    • Alkaline earth metals (2): reactive, lose 2 e⁻

    • Halogens (17): very reactive nonmetals, gain 1 e⁻

    • Noble gases (18): inert, full valence shells

3. Valence Electrons & Periods

  • Group 1 → 1 valence e⁻, Group 2 → 2, … Group 18 → 8 (He = 2)

  • Period # = highest principal energy level of valence e⁻

4. Periodic Trends

Trend

Across Period →

Down Group →

Reason

Atomic radius

↓

↑

Nuclear pull vs. more energy levels

Ionic radius

cations ↓, anions ↓

↑

Cations lose e⁻, anions gain e⁻; more orbitals down group

Ionization energy

↑

↓

Stronger nuclear pull across, less down group

Electronegativity

↑

↓

Atoms pull electrons stronger → smaller radius across period

Octet rule

Gain, lose, share e⁻ → 8 valence

N/A

Explains ionic formation

5. Electron Configurations & Blocks

  • s-block: ends in s¹–², Groups 1–2 + He

  • p-block: ends in p¹–⁶, Groups 13–18

  • d-block: ends in d¹–¹⁰, Groups 3–12

  • f-block: ends in f¹–¹⁴, Lanthanides/Actinides

  • Key tip: Group # = valence electrons (s & p blocks)

6. Ion Formation

  • Cations (+): smaller → lose valence e⁻ → less repulsion

  • Anions (-): larger → gain e⁻ → more repulsion

  • Ionization energy: energy to remove e⁻ → ↑ across period, ↓ down group

7. Quick Memory Tips

  • “FONClBrISCH” = common diatomic nonmetals: F₂, O₂, N₂, Cl₂, Br₂, I₂, S₈, H₂

  • Reactivity:

    • Metals ↑ down group, left → more reactive (lose e⁻ easily)

    • Nonmetals ↑ up group, right → more reactive (gain e⁻ easily)

  • Blocks shape the table: s (2 cols), p (6 cols), d (10 cols), f (14 cols)