Electronic configuration of Group–1 elements

Element	At. no	Complete electronic configuration	Valence shell electronic configuration
Li	3	2, 1 or [He] 2s1	2s1
Na	11	2, 8, 1 or [Ne] 3s1	3s1
K	19	2, 8, 8, 1 or [Ar] 4s1	4s1
Rb	37	2, 8, 18, 8, 1 or [Kr] 5s1	5s1
Cs	55	2, 8, 18, 18, 8, 1 or [Xe] 6s1	6s1
Fr	87	2, 8, 18, 32, 18, 8, 1 or [Rn] 7s1	7s1