K L MNa - 11 - 2 8 1
Valence shell - MValence electrons - 1
Core electrons - 2 + 8 = 10
The electronic configurations of some of the elements are detailed below. How many valence and core electrons do the following have?
- Al: 2, 8, 3
- Mg: 2, 8, 2
- Cl: 2, 8, 7
- Ca: 2, 8, 8, 2.
- Valence electrons = 3; core electrons = 10
- Valence electrons = 2; core electrons = 10
- Valence electrons = 7; core electrons = 10
- Valence electrons = 2; core electrons = 18
Significance of valence electrons
- Valence electrons of an atom are responsible for chemical reactions as they take part in them.
- Elements having same number of valence electrons in their atoms possess similar chemical properties. All alkali metals have one valence electron in their atom. Thus, their chemical properties are similar.
- Elements having 1, 2 or 3 electrons in the valence shell are metals. Exception is H and He. Elements having 4 to 7 electrons in their valence shell are non-metals.
Lets try out:
Classify the following elements as metals or non-metals:
A - 2,8,2 - It is a metal as it has 2 valence electronsB - 2,8,6 - It is a non-metal as it has 6 valence electrons
C - 2,6 - It is a non-metal as it has 6 valence electrons
- The number of the valence shell in an atom determines the period number to which the elements belong in the Periodic Table.
Na - 11 : 2, 8, 1Number of the valence shell - 3
Therefore, sodium is placed in period 3 of the periodic table.
Ca - 20 : 2, 8, 8, 2Number of the valence shell - 4
Therefore, sodium belongs to period 4 of the periodic table.