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Hi, I'm doing a review on electron configuration, but I seem to have forgotten the pattern or order behind determining configuration. So if I randomly picked an element on the periodic table, what steps would I need to take to determine its electron configuration and noble gas configuration? Let's do Silicon and Bromine's electron and noble gas configurations as examples. And what were the exceptions Professor Lavelle was talking about? Thank you in advance!
Hi! There's actually a really handy diagram that helps you determine electron configuration of an atom much easier. For Si, the electron configuration would be 1s^2 2s^2 2p^6 3s^2 3p^3. For its noble gas configuration, use the noble gas that precedes it. In this case, it would be Neon. The noble gas electron configuration would be [Ne] 3s^2 3p^3. For Bromine, its electron configuration would be 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^5. Its noble gas configuration would be [Ar] 4s^2 3d^10 4p^5. The exceptions are chromium and copper, whose electron configurations are [Ar] 3d^5 4s^1 and [Ar] 3d^10 4s^1, respectively. The reason for this is because there would be a lower total energy if an electron enters the 3d subshell instead of the 4s subshell if a half subshell or full subshell is completed.
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