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Periodic Table & Chemical Bonding

Periodicity, ionic and covalent bonding, VSEPR, hybridisation, and coordination compounds

Key Concepts
  • Atomic radius decreases across a period and increases down a group
  • Ionisation energy and electronegativity rise across a period
  • Ionic bonding (electron transfer) vs covalent bonding (electron sharing)
  • VSEPR and hybridisation (sp, sp², sp³) predict molecular geometry
  • Coordination compounds: crystal field theory and isomerism
Important Formulae
Bond order (MOT) BO = (N_b − N_a)/2
Formal charge FC = V − N − B/2
Dipole moment μ = q × d
Effective nuclear charge Z_eff = Z − σ
Quick Tips
  • Lone pairs repel more than bonding pairs, reducing bond angles (H₂O 104.5°, NH₃ 107°).
  • Bond order of 0 means the molecule does not exist (e.g. He₂).
  • Half-filled and fully-filled orbitals give extra stability (Cr, Cu exceptions).
Sample Practice Questions

  1. Down a group, the first ionisation energy generally:

    • Increases
    • Decreases
    • Stays the same
    • Becomes zero
    Show answer

    Answer: Decreases

  2. The molecular shape of methane (CH₄) is:

    • Linear
    • Trigonal planar
    • Tetrahedral
    • Octahedral
    Show answer

    Answer: Tetrahedral

  3. Across a period (left to right), the atomic radius generally:

    • Increases
    • Decreases
    • Stays the same
    • Doubles
    Show answer

    Answer: Decreases

  4. The most electronegative element in the periodic table is:

    • Oxygen
    • Chlorine
    • Fluorine
    • Nitrogen
    Show answer

    Answer: Fluorine

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Practice Questions

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