Basic assumption of electronic theory of valency

The outermost shell of an atom is known as the valence shell. The electrons present in the valence shell are called valence electrons.

K L M

Na - 11 - 2 8 1

Valence shell - M

Valence electrons - 1

Core electrons - 2 + 8 = 10

Question

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.

Solution

  • Valence electrons = 3; core electrons = 10
  • Valence electrons = 2; core electrons = 10
  • Valence electrons = 7; core electrons = 10
  • Valence electrons = 2; core electrons = 18

valence electrons features

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.

electrons Valence significance

  • 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 electrons

B - 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.

Example

Na - 11 : 2, 8, 1

Number of the valence shell - 3

Therefore, sodium is placed in period 3 of the periodic table.

Example

Ca - 20 : 2, 8, 8, 2

Number of the valence shell - 4

Therefore, sodium belongs to period 4 of the periodic table.

1 comment:

Inuojo Olamilekan said...

please correct the last statement sir..calcium is in period 4 and not sodium..i believe it's an oversight error...keep up the good work sir