If you can understand the title of this post, congratulations to you, you have learned one of the fundamental topics of chemistry. "The Aufbau Principle" states that electrons fill orbitals from the lowest possible energy states before filling higher states. So don't marvel that you can see that 3 comes first then 4 then back to three. If you only know how the periodic table is structurized, you can easily tell what comes next. Chemistry is a douchebag,...
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