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Trends in Electron (electronic) Configuration

Key Concepts

  • Trends in number of valence electrons (electrons in the highest energy level):

    • Elements in the same Group of the Periodic Table have the same number of valence shell electrons (electrons in the highest energy level).

    • Going across a period of the Periodic Table from left to right the number of valence electrons increases.

  • Trends in energy of valence electrons:

    • The valence shell electrons of elements in the same Period of the Periodic Table occupy the same energy level (shell).*

    • Going down a Group of the Periodic Table from top to bottom, the energy of the valence shell electrons increases.
*This discussion excludes transition elements, actinides and lanthanides

Trends in the Number of Valence Electrons

H
1
 
symbol
simple electron configuration
(valence shell electrons, the number of electrons in the highest energy level, shown in bold)
He
2
 

Group 1
(IA)
Group 2
(IIA)
Group 13
(IIIA)
Group 14
(IVA)
Group 15
(VA)
Group 16
(VIA)
Group 17
(VIIA)
Group 18
(VIIIA or 0)
Li
2,1
Be
2,2
  B
2,3
C
2,4
N
2,5
O
2,6
F
2,7
Ne
2,8
Na
2,8,1
Mg
2,8,2
  Al
2,8,3
Si
2,8,4
P
2,8,5
S
2,8,6
Cl
2,8,7
Ar
2,8,8
K
2,8,8,1
Ca
2,8,8,2
Ga
2,8,18,3
Ge
2,8,18,4
As
2,8,18,5
Se
2,8,18,6
Br
2,8,18,7
Kr
2,8,18,8
Rb
2,8,18,8,1
Sr
2,8,18,8,2
In
2,8,18,18,3
Sn
2,8,18,18,4
Sb
2,8,18,18,5
Te
2,8,18,18,6
I
2,8,18,18,7
Xe
2,8,18,18,8
Cs
2,8,18,18,8,1
Ba
2,8,18,18,8,2
Tl
2,8,18,32,18,3
Pb
2,8,18,32,18,4
Bi
2,8,18,32,18,5
Po
2,8,18,32,18,6
At
2,8,18,32,18,7
Rn
2,8,18,32,18,8
Fr
2,8,18,32,18,8,1
Ra
2,8,18,32,18,8,2
1 valence electron 2 valence electrons 3 valence electrons 4 valence electrons 5 valence electrons 6 valence electrons 7 valence electrons 8 valence electrons
(EXCEPTION He has 2 valence electrons)

Elements in the same Group have the same number of valence shell electrons.

Group1
(IA)
2
(IIA)
13
(IIIA)
14
(IVA)
15
(VA)
16
(VIA)
17
(VIIA)
18
(VIIIA or 0)
No. valence electrons12345678*

*Helium is an exception since it has only 2 valence electrons
Across a period of the Periodic Table from left to right the number of valence electrons increases.*

Group1
(IA)
2
(IIA)
13
(IIIA)
14
(IVA)
15
(VA)
16
(VIA)
17
(VIIA)
18
(VIIIA or 0)
No. valence electrons12345678*
lowest number of
valence electrons
highest number of
valence electrons

*Helium is an exception since it has only 2 valence electrons

Trends in Energy of Valence Electrons

H
1s1
symbol
position of valence shell electrons (energy level of valence electrons shown in bold)

Period Group 1
(IA)
Group 2
IIA
Group 13
(IIIA)
Group 14
(IVA)
Group 15
(VA)
Group 16
(VIA)
Group 17
(VIIA)
Group 18
(VIIIA or 0)
Energy Level of Valence Electrons
1 He
1s2
1
(K shell)
Lowest Energy
2 Li
2s1
Be
2s2
  B
2s22p1
C
2s22p2
N
2s22p3
O
2s22p4
F
2s22p5
Ne
2s22p6
2
(L shell)
3 Na
3s1
Mg
3s2
  Al
3s23p1
Si
3s23p2
P
3s23p3
S
3s23p4
Cl
3s23p5
Ar
3s23p6
3
(M shell)
4 K
4s1
Ca
4s2
Ga
4s24p1
Ge
4s24p2
As
4s24p3
Se
4s24p4
Br
4s24p5
Kr
4s24p6
4
(N shell)
5 Rb
5s1
Sr
5s2
In
5s25p1
Sn
5s25p2
Sb
5s25p3
Te
5s25p4
I
5s25p5
Xe
5s25p6
5
(O shell)
6 Cs
6s1
Ba
6s2
Tl
6s26p1
Pb
6s26p2
Bi
6s26p3
Po
6s26p4
At
6s26p5
Rn
6s26p6
6
(P shell)
7 Fr
7s1
Ra
7s2
7
(Q shell)

Highest Energy

The valence shell electrons of elements in the same period of the Periodic Table occupy the same energy level:
PeriodEnergy Level of
Valence Electrons
Valence Shell
11K
22L
33M
44N
55O
66P
77Q

Down a Group of the Periodic Table from top to bottom, the energy of the valence electrons increases:
Energy Level of
Valence Electrons
in a Group
2lowest energy
3
4
5
6
7highest energy


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