Line Spectra - Why do they occur? What about the reverse spectra, where you have a continuous spectrum with some lines of black?
Bohr's Atom - Energy levels in atoms. Electrons transfer from one energy level to the other. When they move up to a higher level, energy (light) is absorbed. When electrons fall back to lower levels, energy (light) is released. When the energy levels are spread apart more, the energy released or absorbed is greater, and the frequency is greater (and the wavelength is shorter).
Orbitals - Quantum mechanics. Electrons exist in orbitals, two electrons per orbital. The shape of an orbital describes the probability that an electron will be found at a certain location. Two electrons can fit in each orbital, and they must have opposite spin.
The principal energy levels (n=1,2,3,... from the Bohr atom) are split into sublevels (s, p, d, f). Each sublevel has a certain number of orbitals. Know the shapes of orbitals in the s, p, and d sublevels. Know the number of orbitals in each of the four types of sublevels, and the number of electrons that can go in each sublevel. Know how you can remember this stuff by looking at the periodic table.
Remember that all atoms have the same energy levels available to be filled. The ground state of an atom is the situation when the electrons fill the lowest available orbitals and sublevels.
Electronic configurations - Know how to write these for every atom. Use the periodic table as guidance.
Lewis structures for atoms - These show the valence electrons only. They also indicate how the valence electrons are paired.
Periodic trends - Know the general directions of trends in atomic radius, ionization energy, and electronegativity.
Know the difference between ionic and covalent bonds. Which ones are molecules? Which ones form crystal lattices? Why? Which ones involve a transfer of electrons? Which ones involve sharing of electrons?