Chemistry :- Classification of elements

Mendeleev periodic table it state that the physical and chemical properties of the element are te periodic function of there atomic weight

Modern periodic law it state that the physical and chemical properties of the elements are the periodic function of there atomic number .

Chemical reactivity :

It is the tendency of elements to lose or gain the electrons depend upon atomic size and number of valence electron .

In group IA,IIA the chemical reactivity increase from top to bottom because they are metal. It is easy to loose the electron for a metal having bigger atomic size .

In group VIA,VIIA the chemical reactivity decrease from top to buttom because they are not metal . it is easy to gain th electron for a non metal having smaller automatic size .

Sub shell electron configuration s,p,d and f;s 2),p,6),d10),f14)

Sub shell electron configuration chromium  Cr,24) 1s2 2s2 2p6,3s2 , 3p6,3d5 ,4s1

Chemical reaction

Combination reaction :

It is a chemical reaction in which teo or more elements or compounds combine to form a new compound .

Decomposition reaction :

It is a chemical reaction in which one compound breaks into two or more molecules or compounds .

Displacement reactions

It is chemical reaction I which an atom or a group of atom is displaced by another atom or group of atom is displaced by another atom or a groups of atoms.

Single displacement reaction :

It is a chemical reaction in which displacement of less active element from a compound occurs by an active metal

Double displacement reaction

It is a chemical reaction in two reacting compod exchange their corresponding redicals of the compound to form new compounds .

Exothermic reaction :-

It is a chemical reaction in which heat is released

Endothermic reaction :

It is chemical reaction in which heat is absorbed form the surrounding.

Rate of chemical reaction :

It is the time taken from the starts of the reaction to its end

Factor affecting the rate of chemical reaction : These are temperature , physical state of the reaction concentration of the reactants

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