valence electrons

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A chemical reaction involves either electron removal, electron addition, or electron sharing. Valence electrons are the electrons in the highest occupied principal energy level of an atom. In the second period elements, the two electrons in the 1s1s sublevel are called inner-shell electrons and are not involved directly in the element's reactivity or in the formation of compounds. To tell how many electrons there are on a principal level

WE USE DE 2N^2, the n stands for energy level

2n^2

2(1)^2=2 S

2(2)^2=8 SP

2(3)^2=18 SPDI

2(4)^2= 32 SPDF

2(5)^2=50 spdfj

The energy levels are the rows, the horizontal lines -------