We all know that potassium, the 19th element on the periodic table has the electronic configuration of 2.8.8.1. However, why not 2.8.9? In the element scandium, it has the electronic configuration of 2.8.9.2. I would like to know why potassium is not 2.8.9.
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i think it’s because that the subshell 3d is of a higher energy then 4s, so by the aufbau principle it will be filled up first. nice to see another asecondary school student in s’pore – Jan 22 '18 at 12:42
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Related: Why isn't the scandium(2+) cation isoelectronic with potassium? and Why do 3d orbitals have lesser energy than 4s orbitals in transition metals? and Why does the 3rd electron shell start filling up with scandium? – orthocresol Jan 22 '18 at 13:55
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You could actually have the 2.8.9 configuration, putting the last electron in a 3d rather than 4s orbital. But the 2.8.8.1 one is lower in energy and thus more stable. How electrons fill subshells in neutral atoms to make the lowest energy configuration can be seen here.
Oscar Lanzi
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