Atoms: what we should know, part I

1) Atoms are composed of a heavy, fixed nucleus which has a positive charge and electrons which are attracted to the positively charged nucleus. Our attention is focused on the electrons, which are light and therefore behave in very interesting and unexpected ways.

2) The electrons in an atom must exist in states which have specific energies. These are called discrete energy states. (Discrete, in this context, means isolated, detached or separate (from other states)-- not part of a continuum.)

3) Transitions in which an electron goes from one discreet energy state to another are the reason behind the sharp-line spectra seen in absorption and emission spectroscopy.

4) The existence of these discrete energy electron states is explained by a "wave theory" of electrons (~1930), which leads to a lowest energy state known as the "ground state" (fundamental), and a sequence of states at higher energies ("harmonics"). This is analogous to the theory of a wave on a string, which leads to a mode of lowest frequency (fundamental) and a sequence of discrete harmonics at higher frequencies.

5) ...to be continued... (see part II)