The document shows the electronic configuration, valence electrons, and group number of several elements (Na, Mg, Al, Si, P, S, Cl). It fills in this information step-by-step to illustrate that all the elements belong to period 3, having their outermost quantum shell (valence shell) as principal quantum number 3. The valence electrons are calculated as the total electrons in the outermost shell.

1. Exercise 1
Elements Na Mg Al Si P S Cl
Electronic
config.
Valence
electrons
Group No.

2. Exercise 1
Elements Na Mg Al Si P S Cl
Electronic [Ne]
config. 3s1
Valence
electrons
Group No.

3. Exercise 1
Elements Na Mg Al Si P S Cl
Electronic [Ne]
config. 3s1
Valence
1
electrons
Group No.

4. Exercise 1
Elements Na Mg Al Si P S Cl
Electronic [Ne]
config. 3s1
Valence
1
electrons
Group No. 1

5. Exercise 1
Elements Na Mg Al Si P S Cl
Electronic [Ne] [Ne]
config. 3s1 3s2
Valence
1
electrons
Group No. 1

6. Exercise 1
Elements Na Mg Al Si P S Cl
Electronic [Ne] [Ne]
config. 3s1 3s2
Valence
1 2
electrons
Group No. 1

7. Exercise 1
Elements Na Mg Al Si P S Cl
Electronic [Ne] [Ne]
config. 3s1 3s2
Valence
1 2
electrons
Group No. 1 2

8. Exercise 1
Elements Na Mg Al Si P S Cl
Electronic [Ne] [Ne] [Ne]
config. 3s1 3s2 3s23p1
Valence
1 2 2+1=3
electrons
Group No. 1 2 3

9. Exercise 1
Elements Na Mg Al Si P S Cl
Electronic [Ne] [Ne] [Ne] [Ne]
config. 3s1 3s2 3s23p1 3s23p2
Valence
1 2 2+1=3 2+2=4
electrons
Group No. 1 2 3 4

10. Exercise 1
Elements Na Mg Al Si P S Cl
Electronic [Ne] [Ne] [Ne] [Ne] [Ne]
config. 3s1 3s2 3s23p1 3s23p2 3s23p3
Valence
1 2 2+1=3 2+2=4 2+3=5
electrons
Group No. 1 2 3 4 5

11. Exercise 1
Elements Na Mg Al Si P S Cl
Electronic [Ne] [Ne] [Ne] [Ne] [Ne] [Ne]
config. 3s1 3s2 3s23p1 3s23p2 3s23p3 3s23p4
Valence
1 2 2+1=3 2+2=4 2+3=5 2+4=6
electrons
Group No. 1 2 3 4 5 6

12. Exercise 1
Elements Na Mg Al Si P S Cl
Electronic [Ne] [Ne] [Ne] [Ne] [Ne] [Ne] [Ne]
config. 3s1 3s2 3s23p1 3s23p2 3s23p3 3s23p4 3s23p5
Valence
1 2 2+1=3 2+2=4 2+3=5 2+4=6 2+5=7
electrons
Group No. 1 2 3 4 5 6 7

13. Exercise 1
Elements Na Mg Al Si P S Cl
Electronic [Ne] [Ne] [Ne] [Ne] [Ne] [Ne] [Ne]
config. 3s1 3s2 3s23p1 3s23p2 3s23p3 3s23p4 3s23p5
Valence
1 2 2+1=3 2+2=4 2+3=5 2+4=6 2+5=7
electrons
Group No. 1 2 3 4 5 6 7
Outermost quantum shell = 3
 the principal quantum number of the valence shell is 3
 all the elements in this period belong to Period 3