Unit 2
Atomic structure
Why do atoms absorb and emit only particular colours? How do electrons stack into orbitals, and where does the shape of the periodic table come from? This unit answers with spectra, quantum numbers, and electron configurations — and finally counts the protons in the nucleus with X-rays.
- 1 Inside the atom: protons, neutrons and electrons How did Rutherford find the nucleus? How do three particle counts pin down an atom or ion? And why is chlorine’s atomic mass 35.45 — a value no chlorine atom has? 20 min
- 2 Light and spectra: the fingerprints of atoms Light’s energy comes in packets: weigh Planck’s constant with the photoelectric effect, then read the lines of hydrogen, helium, neon, sodium and mercury — and the colours of flames. 25 min
- 3 The quantum model: orbitals and quantum numbers Electrons are waves too. Rotate hydrogen orbitals computed from the Schrödinger equation, count their nodes, and learn what n, l, mₗ and mₛ each control. 25 min
- 4 Electron configuration: filling the orbitals Place electrons one at a time using three rules — lowest energy first, Pauli exclusion, and Hund’s rule — and watch the shape of the periodic table grow out of them. 25 min
- 5 Periodic trends: size, ionization energy and electronegativity Predict, then check the data: explain atomic size, ionization energy, electron affinity and electronegativity with effective nuclear charge, and count valence electrons from successive ionization energies. 25 min
- 6 X-rays and atomic number: Moseley’s law Transitions of inner electrons give characteristic X-rays whose energy grows as (Z − 1)²: from this Moseley proved that the periodic table is ordered by nuclear charge. Then identify the elements in stainless steel, solder and soil from their X-ray fluorescence. 30 min