Question

How many total electrons and valence electrons are found in an atom of each of the following elements? What is the number of the principal energy level in which the valence electrons are found? 

a. Mg b. K c. C d. Br e. Ar

Answer 1

Mg ( Electrons per shell 2, 8, 2) = 12 total electrons

[Ne]3s² = 2 valance electrons (n=3 is the PE level with VE)

Bromine is element ( Electrons per shell 2, 8, 18, 7) = 35 total electrons

[Ar] 4s23d104p5 = 7 valance electrons (n=4 is the PE level with VE)

K ( Electrons per shell 2, 8, 8, 1) = 19 total electrons

[Ar] 4s1 = 1 valance electrons (n=4 is the PE level with VE)

Ar ( electrons per shell 2, 8, 8) = 18 total lectrons

[Ne] 3s2 3p6 = 8 valance electrons (n=3 is the PE level with VE)

C ( electrons per shell 2,4) = 6 total electrons
[He] 2s2 2p2 = 4 electron ( n= 2 is the PE level with VE)

Xe ( Electrons per shell 2, 8, 18, 18, 8) = 54
[Kr] 4d10 5s2 5p6 = 8 valance electrons (n=5 is the PE level with VE)