What Determines Atomic Size?
A big problem with the nuclear hydrogen atom was: what determined its size? Classical mechanics gives a simple dynamical equation for circular orbits: . Now this equation is satisfied by any circular orbit centered at the nucleus, however large or small. (Note, by the way, that multiplying both sides by r/2 gives that the magnitude of the kinetic energy in the circular orbit is just half the magnitude of the negative potential energy. We need this below.) There is no hint here that the atom in its “natural” ground state should have any particular radius. But it does! This means we’re missing something. But what? Bohr (and others) thought that Planck’s constant must somehow play a role in determining the size of the orbit. After all, it did play a role in restricting allowed orbital changes in the oscillators in black body radiation — and these oscillators, although not very clearly understood, were of the same general size as atoms. So evidently the standard picture of how an oscillat
Related Questions
- What are the group trends in melting point, boiling point, reactivity, size of atom (atomic radius), density and physical strength as you go down the group 1 alkali metals as the atomic/proton number increases?
- What effect does an additional proton have on atomic size?
- Why is potassium larger than iodine(atomic size)?
