The following table represents the first 20 elements of the Periodic table (the symbol and the electronic configuration for the outermost shell for each of the 20 elements are given).
IA 0
H
1
IIA IIIA IVA VA VIA VIIA
He
2
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

The outermost shell electrons are also known as _____ electrons.

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Solution

Valence electrons of an element are defined as the number of electrons present in the outermost shell of that element.
Valence electrons in any element in Group 1, 2, and 13 to 18 can be predicted by its Group number.
Elements in Group 1 and Group 2 have 1 and 2 valence electrons, respectively.
In the case of Group 13 to 18, the formula to calculate the number of valence electrons is:
$Number of valence electrons = Group number - 10$
Hence, the outermost shell electrons are also known as valence electrons.

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