Constituents of the Atom
Atoms as understood in 1930:
- electrons, negatively charged “particles” described in terms of quantum states (solutions to Schrodinger’s equation).
- protons, the heavy positive nucleus of the hydrogen atom
- nuclei, positively charged (must be composed of something more fundamental from which are made the many nuclei observed)
- 1932: Chadwick observes a penetrating neutral radiation produced in the collision of alpha particles with berylium, the neutron, whose mass is close to that of the proton.
Great success & simple picture:
- All elements are composed of three constituents, electrons, protons and neutrons. One other fundamental entity, the photon (the quantum of electromagnetic radiation) is produced when electrons change states in the atom.
- A given element is defined in terms of how many electrons (which equals the number of protons) it has. Different isotopes correspond to different numbers of neutrons in the nucleus.