Identify the number of core and valence electrons for each atom.

Question

Ar:

Be:

Br:

Answer 1

Ar: [Ne]3s2 3p6 has 10 core electrons and 8 valence electrons

Be: 1s2 2s2 has 2 core electrons and 2 valence electrons

Br: [Ar] 4s2 3d10 4p5 has 28 core electrons and 7 valence electrons