Chapter 2 chemical bonding :

 Stability and energy :

  Stability of a system is related to its energy .when energy increases stability decreases .hence each system tries to attain stability by reducing its energy .It will adopt  the most suitable means,  for this an object at a great height tends to come down to lower height to attain stability by reducing energy.

Element       atomic number      electronic                                                                    configuration                      

Helium(He)           2                     2

Neon (Ne)            10                    2,8

Argon(Ar)              18                   2,8,8

Krypton (kr)           36                  2 ,8,18,8

Xenon(Xe)               54                 2,8,18,18,8

Radon (Rd)              86                2,8,18,32,18,

The elements in the last column of periodic table are Helium , Neon ,Argon, krypton, Xenon and Radon .  Since since these elements have maximum stability, they are known as Noble elements and all of them are gases they are also known as noble gases. While atoms of other elements form molecules of that element  or molecules of a compound to attain stability , the nobel elements are stable in their atomic state itself . It's is due to this stability that they retrain from entering into chemical reaction. So they are also known as inert gas.

          

            Specialties of electronic configuration of these elements different of that of other elements except Helium,  all others have 8 electrons in outermost shell.

Questions:

1) what is the reason for the stability of the noble element?

       The reason  for the stability of noble elements is the presence of 8 electrons in it's outermost shell.

2) how do other element attain stability?

       

         The other elements attain stability by getting 8 electrons in the outermost shell.

Octet arrangement:

The State in which 8 electrons are present in the outermost shell is known as octet arrangement. Having 8 electrons in the outermost shell is the situation to attain the least energy level in an atom.

Relation between stability and electronic configuration:

Except Helium, all other Nobel elements have 8 electrons in the outermost shell. Hence the atom is at the lower energy state. So the noble elements naturally have the stable structure. 

They combined with other elements only rarely.

Stability of helium atom :

Helium,  which is the smallest atom among  inert elements and it has only one shell. The maximum number of electrons that can be accommodated in the first shell is  2. Hence, two electron arrangement (duplet arrangement) is stable in the case of helium. 

Q) why don't inert gas take part in chemical reaction?

 

         Atoms  take part in chemical reaction to attain octet electronic configuration in the outermost shell by decreasing the energy to the maximum extent . Hence the inert gas have octet configuration in the outermost shell and  they are already stable. So inert gas don't enter in chemical reaction.

Valence shell and valence electrons 

       The outermost shell of an atom is called valence shell and the number of electrons in the valency shell is called valence electron.

Ex:

1.Sodium (Na-11)

Electronic configuration: 2, 8, 1

Valence shell : M

Valence electron :1

2.chlorine  (Na-17)

Electronic configuration: 2, 8, 7

Valence shell : M

Valence electron :7

3.carbon (C-6)

Electronic configuration: 2, 4

Valence shell : L

Valence electron :4

Q) How many ways atom attain octet electronic configuration? 

           when atoms combine they obtain octet electron configuration either by accepting or by donating or by sharing electrons.