Chemistry · Ch 2 — Quantum Mechanical Model of Atom
Introduction
Introduction
This unit picks up the story of atomic structure where Bohr's model left off, and asks a deeper question: if Bohr's fixed circular orbits explain hydrogen's spectrum so well, why do they fail for every atom with more than one electron?
What this unit sets out to do. By the end of it you should be able to:
- recognise the historical progression of atomic models, and the specific experimental result each one was built to explain;
- explain the dual (wave-and-particle) behaviour of matter, and derive de Broglie's equation for the wavelength of a moving particle;
- state and apply Heisenberg's uncertainty principle to simple numerical problems;
- appreciate what each of the four quantum numbers -- principal, azimuthal, magnetic and spin -- tells you about an electron;
- summarise the key features of the quantum mechanical (Schrodinger) model of the atom, and sketch the shapes of the s, p and d orbitals;
- apply the Aufbau principle, Hund's rule and Pauli's exclusion principle together to write the electronic configuration of an atom.
Erwin Schrodinger, whose wave equation gives this unit its modern picture of the atom, wasn't satisfied with the quantisation rule Bohr simply assumed -- that angular momentum must be a whole-number multiple of h/2pi -- he wanted an equation that predicted it instead of asserting it. That search is why quantum mechanics replaces Bohr's neatly drawn orbits with the fuzzier, evidence-based idea of an orbital: a three-dimensional region where an electron is likely to be found.