Chemistry

Lessons

1. 01

   Atomic structure

   Atoms are made of protons, neutrons and electrons. Z (protons) fixes the element; A counts protons plus neutrons; the charge counts missing or extra electrons.

2. 02

   Quantum theory

   Light comes in photons with energy E = hν. Electrons in atoms can only have certain energies, so atoms absorb and emit light only at particular wavelengths. Electrons are described by orbitals labelled by quantum numbers.

3. 03

   Periodic table

   Electron configurations follow from filling orbitals in order of energy. The periodic table groups elements with similar outer electrons, and effective nuclear charge explains the trends in size, ionisation energy and electronegativity.

4. 04

   Chemical bonding

   Atoms bond by transferring electrons (ionic) or sharing them (covalent). Lewis structures count the electrons; VSEPR turns electron domains into shapes; shape and electronegativity decide polarity.

5. 05

   Intermolecular forces, phases and solubility

   Forces between molecules — dispersion, dipole–dipole, hydrogen bonding and ion–dipole — decide boiling points, phase changes and which substances mix.

6. 06

   Writing formulas and naming compounds

   Write formulas from ion charges and name ionic and molecular compounds so that the formula, the name and the charges always agree.

7. 07

   Moles, molar mass and chemical formulas

   The mole links the particles in a formula to the grams on a balance: n = m/M and N = nN_A. Formulas give atom ratios, percentage composition and empirical formulas.

8. 08

   Reactions in solution

   In water, many compounds exist as ions. Reactions in solution — precipitation, acid–base and redox — are written as net ionic equations, and their amounts are calculated through moles using balanced equations.

9. 09

   Properties of solutions

   A solution’s composition is described by concentration units (molarity, molality, mass percent, mole fraction). Dilution conserves solute. Dissolved particles lower vapour pressure and freezing point and raise boiling point and osmotic pressure.

10. 10

    Properties of gases

    An ideal gas obeys PV = nRT with T in kelvin. The simple gas laws, gas densities, mixtures (Dalton) and gas stoichiometry all follow, and kinetic-molecular theory explains why.

11. 11

    Thermochemistry

    Reactions release or absorb heat. Measure heat with q = mcΔT (calorimetry); express reaction heats as ΔH; combine them with Hess’s law, enthalpies of formation or bond enthalpies.

12. 12

    Electrochemistry

    Redox reactions can be split so that electrons flow through a wire. Galvanic cells convert chemical energy to electrical energy (E°cell = E°cathode − E°anode); electrolysis uses electricity to drive non-spontaneous reactions (Faraday’s laws).