The Atom: Planetary Model, Bohr's Postulates, Lasers and X-Rays
How physicists worked out what is inside an atom, and how that knowledge gave us lasers and X-ray images.
Big Idea: An atom is almost entirely empty space with a tiny, heavy, positive nucleus at its centre and light electrons far outside it. Electrons are only allowed to have certain fixed energies. An atom gives off or absorbs light in single packets called photons whenever an electron jumps from one allowed energy to another. Controlling those jumps is exactly what a laser does, and knocking electrons hard onto a metal target is how we make X-rays.
By the end of this lesson you will be able to:
- describe Rutherford's gold-foil experiment and the planetary (nuclear) model it produced,
- explain why the planetary model fails according to classical physics,
- state Bohr's two postulates and use hν = Em − En,
- read an energy-level diagram and calculate the energy and wavelength of an emitted photon,
- explain how a laser and how X-rays are produced and where they are used.