Identify the outer electron configurations for the (a) alkali metals, (b) alkaline earth metals, (c) halogens, (d) noble gases.

a) Alkali metals

=> group 1

=> Li: 1s2 2s = > 1s

Na: [Ne] 3s = > 3s

K: [Ar] 4s = > 4s

Rb: [Kr] 5s = > 5s

Cs: [Xe] 6s = > 6s

Fr: [Rn] 7s = > 7s

=> outer electron configuration is ns, where n is the main energy level: 1, 2, 3, 4, 5, 6,7.

b) Alkaline earth metals

=> group 2 = > you have to add 1 electron to the alkaly metal of the same row.

=> Be: [He] 2s2 = > 2s2

Mg: [Ne] 3s2 = > 3s2

Ca: [Ar] 4s2 = > 4s2

Sr: [Kr] 5s2 = > 5s2

Ba: [Xe] 6s2 = > 6s2

Ra: [Rn[ 7s2 = > 7s2

=>outer electron configuration is n s2, where n is the main energy level: 1, 2, 3, 4, 5, 6, 7

c) halogens

=> group 7

=> F: [He] 2s2 2p5 = > 2s2 2p5

Cl: [Ne] 3s2 3p5 = > 3s2 3p5

Br: [Ar] 3d10 4s2 4p5 = > 4s2 4p5

I: [Kr] 4d10 5s2 5p6 = > 5s2 5p5

At: [Xe] 4f14 5d10 6s2 6p5

=> outer electron configuration is ns2 np5, where n is the main energy level 1, 2, 3, 4, 5, 6, 7

d) Noble gases

=> group 8

I will show only the outer shell which is what is requested

=> He: 1s2

Ne: ... 2s2 2p6

Ar: ... 3s2 3p6

Kr: ... 4s2 4p6

Xe: ... 5s2 5p6

Rn: ... 6s2 6p6

=> the outer electron configuration is ns2 np6, except for He for which it is 1s2