General Chemistry: Structure of Matter, Atomic Structure, Periodic Table and Bonding
What you must understand
Start with the atom: protons and neutrons in the nucleus, electrons in shells/subshells (s, p, d, f) filled by the Aufbau principle, Pauli exclusion principle and Hund's rule. Know the four quantum numbers and what each describes. Convert between atomic number Z, mass number A, neutrons (A − Z), and recognise isotopes (same Z, different A), isobars and ions. Relate electron configuration to the periodic table: groups = valence electrons, periods = occupied shells; trends in atomic radius, ionisation energy, electron affinity and electronegativity across periods and down groups.
Bonding follows from electron configuration. Ionic bonding transfers electrons between a metal and non-metal; covalent bonding shares electrons (single, double, triple, polar vs non-polar); metallic bonding involves delocalised electrons. Use VSEPR to predict shapes (linear, trigonal planar, tetrahedral, trigonal pyramidal, bent) and bond angles. Distinguish intermolecular forces: hydrogen bonds, dipole–dipole, London dispersion, and link them to boiling point and solubility. Know the types of crystal lattice (ionic, molecular, covalent network, metallic) and typical properties.
Traps
Questions often confuse mass number with relative atomic mass (a weighted average of isotopes). Watch for ions - electron count changes, not proton count. A polar bond does not guarantee a polar molecule (CO₂ is non-polar). Hydrogen bonding requires H bonded to N, O or F only.
Rule of thumb
For any particle: protons = Z, electrons = Z − charge, neutrons = A − Z. Check the arithmetic before choosing an answer.
Worked example
Chlorine-37: Z = 17, so 17 protons, 17 electrons (neutral), 20 neutrons. As Cl⁻: 18 electrons.