# Postulates of Dalton’s atomic theory free pdf 2022

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## Postulates of Dalton’s atomic theory free

Que 1- What are the postulates of Dalton’s atomic theory of matter ?

Ans (i) Each substance is made up of extremely small particles called atoms.
(ii) Atoms of a given element are identical in mass and chemical properties.
(iii) Elements are substances having the same kind of atoms. In other words, atoms of a particular element are all alike but differ from atoms of other elements. For example,hydrogen gas is composed of atoms of hydrogen while oxygen gas is composed of atoms of oxygen.

(iv) Atoms cannot be created nor destroyed. For example, atoms of a particular element
cannot be converted into atoms of another element by chemical reactions.
(v) Compounds (molecules) are formed by the chemical union of atoms of two or more elements in a fixed proportion which are simple whole numbers.

Que 2- How will you explain the laws of constant proportion on the basis of Dalton’s atomic theory ?

Ans– Explanation on the basis of Dalton’s atomic theory. According to Dalton’s atomic theory, each element consists of atoms which are similar and have same weights. Further atoms of one element combine with atoms of another to form compounds. Let us suppose that x atoms of element A combine with y atoms of element B and the compound formed is AxBy (Dalton’s atomic theory). If ‘a’ stands for the atomic mass of A and b’for that of B, then

Percentage of A in the compound=ax x 100/ ax + by
Percentage of B in the compound = by x 100/ax + by
Now a and b(atomic masses of elements) are fixed, x and y are also fixed whole numbers according to atomic theory. Therefore per cent of A and B in the compound is also constant. This shows that the composition of various elements in a compound is also fixed. This is the law of constant proportion.

Que 3-Hydrogen and oxygen combine in two different ways to produce water and hydrogen peroxide. Which of Dalton’s law does this observation conform ? Explain.

Ans– In water 1 g of hydrogen combines with 8 g of oxygen. And in hydrogen peroxide, 1 g of hydrogen combines with 16 g of oxygen. The ratio of oxygen in water and hydrogen peroxide combining with the same amount of hydrogen i.e., 1 g is 8 : 16 or 1 : 2-a small integral ratio. This is law of multiple proportions which defines as under.
When two elements combine to form more than one compound, the masses of one element that combine with a given mass of the other element in different compounds are in the ratio of small whole numbers.

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