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Dalton atomic Theory and Laws of stoichiometry

Laws of chemical combination stoichiometry 1 728

Dalton's Atomic Theory (Dalton in 1808)

Main Postulates:

1.All matters are made of small particles i. e atoms

2.Atoms of same elements are indentical whereas atoms of different elements are different in all respect i.e shapes, size, weight, and properties.

3.Atoms is the smallest particles that takes part in chemical reactions.

4.Atoms cannot be splitted and created during chemical reaction.

1.Laws of Stiochiometry

In greek, stiochio means an elements and metry means measure which simply forms the measure of elements in combination.

Stiochiometry means The calculations which deals with the mass and volume relationships between reactants and products.There are laws of the Stiochiometry which are discussed below :

1.1:Law of conservation of mass

    It was proposed by lavoiser and verified by landolt. According to this law; Total number of mass remains conserved during chemical reactions", "Mass is neither created nor destroyed in a chemical reaction"

    concept :

    consider a chemical reaction,

        A + B --------> C + D

        According to this laws, 

        mass of A + Mass of B = Mass of C + Mass of D 

        ie. Total mass of reactants =Total mass of the products


1.2 Law of Constant Proportion/composition 

   It was proposed by Proust. 

   it states that "A chemically pure same compound always contains the same elements combined together in the definite proportion by weight regardless of the origin or mode of formation 

   For example :

   Pure water Always contains hydrogen and oxygen in ratio 1:8 by weight. 


1.3 Law of Multiple Proportions 

    It was proposed by Dalton and verified by Berzelius. 

    It states "When two elements combine to form more than one compound then the different masses of one element which combine with a fixed mass of other elements, bear a simple whole number ratio" 

    FOR example :

    Hydrogen and Oxygen combines to form two compounds water and hydrogen peroxide. 


                  Hydrogen              Oxygen 

  in water:   2 parts                 16 parts

  in Hydrogen peroxide :2 parts 32 parts

  Thus, the weight of oxygen which combines with the same weight of Hydrogen(i. e 2 parts by weight) are in the simple ratio of 1:2. This is simple whole number. Hence, it illustrate the law of multiple proportions. 


1.4 Law of reciprocal proportions

  Proposed by Ritcher. 

  It states that" When two elements combine separately with a fixed mass of a third element, then the ratio of their masses in which they do so is either same or some whole number multiple of ratio in which they combine with each other. 



1.5 Gay lussac's law of gaseous volumes

It states "The volumes of the gaseous reactants and products in a chemical reaction bear a simple ratio(i. e simple whole number ratio) if the volumes are measured at similar conditions of temperature and pressure" 

concept :

Considering a chemical reaction 

H2+ Cl2 ------------------> 2HCL 

1 volume 1 volume. 2 volume 

volume of H2:Cl2:HCL which is simple whole no. ratio. 

hence it illustrates the law of gaseous volumes.