Posted: May 25, 2016 9:19 pm
I think you're coming at the problem backwards. It's the protons that are important. The electrons are merely a means for balancing charge, and what we observe in chemistry seldom reflects what we would expect when considering each atom by itself.
I don't understand where you got the impression that the transition metals almost all have one or two valence electrons. Are you discussing shell filling conventions or the types of ions typically formed? I think some clarification is required here. Don't feel bad. Chemistry was both my favorite course and also the one where I literally cried and threw my book at the wall.
The apparent randomness of which elements are considered to have how many electrons in their outer shell is due to relative energy levels of the various sub-shells. Perhaps this bit from wikipedia will help you out:
Things get wonky with the metals because the d-sub-shell electrons are very close, energetically, to the s-sub-shell electrons. Whereas with the non-metals we get to basically ignore all but the s and p sub-shells when considering valence conformations. How comfortable are you with the sub-shells? This is probably the point where you'll find clarity regarding outer shell fullness.
I don't understand where you got the impression that the transition metals almost all have one or two valence electrons. Are you discussing shell filling conventions or the types of ions typically formed? I think some clarification is required here. Don't feel bad. Chemistry was both my favorite course and also the one where I literally cried and threw my book at the wall.
The apparent randomness of which elements are considered to have how many electrons in their outer shell is due to relative energy levels of the various sub-shells. Perhaps this bit from wikipedia will help you out:
https://en.wikipedia.org/wiki/Electron_shellWikipedia wrote:The valence shell is the outermost shell of an atom. It is usually (and misleadingly) said that the electrons in this shell make up its valence electrons, that is, the electrons that determine how the atom behaves in chemical reactions. Just as atoms with complete valence shells (noble gases) are the most chemically non-reactive, those with only one electron in their valence shells (alkali metals) or just missing one electron from having a complete shell (halogens) are the most reactive.[8]
However, this is a simplification of the truth. The electrons that determine how an atom reacts chemically are those that travel farthest from the nucleus, that is, those with the highest energy. For the transition elements, the partially filled (n − 1)d energy level is very close in energy to the ns level[9] and hence the d electrons in transition metals behave as valence electrons although they are not in the so-called valence shell.
Things get wonky with the metals because the d-sub-shell electrons are very close, energetically, to the s-sub-shell electrons. Whereas with the non-metals we get to basically ignore all but the s and p sub-shells when considering valence conformations. How comfortable are you with the sub-shells? This is probably the point where you'll find clarity regarding outer shell fullness.