Posted 21 August 2005 - 03:11 AM
Infernity,
No doubt your physics professor would give an evasive answer. That's my experience, at least.
I can give a quick, fairly easy to understand explaination for you. The electron orbitals are based on solutions to Schrodinger's equation, which is an equation that tells you probabilistically where an electron is most likely to be. They are not merely orbiting around in a circle as the Bohr model suggests, in fact they make some very strange orbital shapes.
The orbital levels are based off of the principle quantum number n, which can be any integer (1, 2, 3...), as the number goes up you need more and more room to accomidate all the extra electrons. The orbitals themselves are called s, p, d, f, and g. However, g doesn't show up at all on the periodic table, and f only in a small section so these are rarely dealt with.
The "s" orbital has only one fill state, it looks like a sphere and most closely resembles a planetary orbit like the Bohr model. Each fill state can hold two electrons (one that spins up, another that spins down).
The "p" orbital looks like a peanut, and it has three fill states. This means it can accomidate six electrons. For the first 3 levels of the periodic table, these are the only orbitals used this is the reason for the octet rule, but it only applies to groups 2 and 3 of the periodic table (those most used in organic chemistry). The s orbital can hold 2, the p orbital can hold 6, for a total of 8 electrons. Atoms want to be filled this way because when the whole orbital is full it is the least reactive it can be. That is, it has the lowest potential energy. If you think of it like a hill, a ball always wants to be at the bottom of the hill because at that point it has the least amount of energy, this same concept works here too.
The "d" orbital has four lobes and takes two shapes, one looks like a four-petal flower, the other like a peanut with a ring around its center. This orbital shows up in the transition metals in the center of the periodic table (like Palladium, which you asked about). It has five fill states and can hold ten electrons. Combined with the s and p orbitals, a d orbital atom can hold 18 electrons in its outer shell. The rare "f" orbital ones have an extra 7 fill states, or 14 electrons and can hold 32 in their outer shell.