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There was a homework problem that asked for the electron configuration of Si and the answer started off with [Ne]. Just curious, why not start off with [Al] (the element immediately preceding Si) so you only have to write [Al]3p2? Is there a rule against doing that?
Generally when shortening electron configuration, we would substitute the preceding noble gas, instead of the immediately preceding element. This allows us to see the electrons in the highest energy level (valence electrons).
It is because we are specifically using the noble gas configuration so you would use the most recent noble gas for your shorthand configuration in efforts to start with the highest amount of valence electrons, since they increase from left to right.
When a problem asks for shorthand electron configuration, I believe they are referring to noble gas configuration, which is why the shorthand of Si starts with the noble gas [Ne].
If the element before Si was a noble gas, we would use that element in the bracket, but since it is not a noble gas, we would use the noble gas that comes before Si, which is [Ne]. You don't have to write your electron configuration this way, but it does come in handy for an element like Lead, whose electron configuration is pretty long.
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