Historical background of clissification of lelements (XII Notes)

                 After Delton Atomic theory the following well known scientists did valuable contribution in the Classification of elements.

Lavoisier.
Dobereiner.
Newland.
Mendeleev.
Moseley.


Lavoisier Classification of elements:


    In 1789 Lavoisier classified 25 to 30 elements in two groups"Metals and non metals"


   * Metals:
              
              Metals are those elements whose oxide and hydroxide are basic in nature,have low ionization potential,
low electron effinity,low electro negativity and high electro positivity.they are good conductor of electricity.
They Malleable,ductile and have a metallic lustre.Most of the metals are exist in solid state.


   *Non Metals:

               The non metals are those elements whose oxides and hydroxides are acidic in nature.Non metals have high
ionization potentials,high electron efinity,high electro negativity and low electropositivity.They are bad conductor of Heat and electricity.
  This classification failed because there are some elements which are called metalloids.
These elements act as a metal as well as non metals.For example. Graphite and silicon has high melting and boiling point but low densities like non metals.Elements having some properties like metals while some properties like non metals are called metalloids.Thus this classification was rejected.

Coulomb Law

Coulomb law definition :

                 Coulomb law state that the force of attraction or repaltion between two bodies acting on a line joining  is.

• Directly proportional to the product of magnitude of  the two charged bodies.
• Is inversely proportional to the distance between them.

What is periodicity in Chemistry and its causes

Periodicity : 

                                  "The repetition  of Certain properties by the elements at a regular interval is known as periodicity".

Causes of periodicity :

   Similarity in the electronic configuration of valence shell of elements is the main cause of periodicity.
Mosely pointed out that !

• Atomic number is the fundamental property of the elements.
• Similar elements are repeated at a regular interval When they arranged in the Increasing order of their atomic number.
• It has been found that atom have same number of electron in their valence shell have similar properties.

 Thank you ~!