Combining Capacity or Valency of Elements


 
 
Concept Explanation
 

Combining Capacity or Valency of Elements

Combining capacity or Valency :

We know that  the outer most shell of an atom is known as  valence shell. The electrons in this outer most shell is known as valence electron. The outer most shell of an atom can accomodate maximum of eight electrons known as complete octet.

As we know that elements with complete octet are non reactive and are  stable . Eg: Noble gases. Elements other than group 18 (noble gases) contain less than 8 electrons in there outer most shell.These atoms are reactive and unstable.To get stability they need to aquire the nearest noble gas configuration with the help of different reactions. During these reactions atoms either gain or lose electrons.The number of electrons lost, gained or shared by an atom determines the valency of the elements concerned. The elements those lose electrons are called as cations and elements those gain electrons are called as anions .

Valency of elements having 1-4 electrons in their outermost shells are determined by the following rule:

Valency =  Number of electrons in the outermost shell

For example: 

  • Hydrogen(H), Lithium(Li), and Sodium(Na) have one electron in their outer most shells. Hence, their valency is 1.
  • Magnesium(Mg) and Aluminium(Al) have 2 and 3 electrons in their outermost shell and hence their valency is 2 and 3 respectively.  
  • Valency of elements with electrons in their outermost shell is close to 8, the valencies are determined by the following rule:
  • Valency = 8 - numbers of electron inthe outermost shell

    For example:

  • Chlorine(Cl) has 7 electrons in its outermost shell. Hence, valency of chlorine is 8 - 7=1.
  • Similarly, Oxygen(O) has 6 electrons in there outermost shell. Hence, its valency is 8-6=2
  • Sample Questions
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    Question : 1

    Aluminium contains __________ electrons in its outermost shell and its valency is also _________.

    Right Option : D
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    Explanation
    Question : 2

    Hydrogen(H), Lithium(Li), and Sodium(Na) have ___________ electron in their outer most shells.

    Right Option : B
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    Explanation
    Question : 3

    The atomic numbers of three elements A, B and C are 10, 18 and 8 respectively. Identify the element which is chemically reactive?

    Right Option : C
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    Explanation
     
     


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