Postulates of Dalton Atomic Theory


 
 
Concept Explanation
 

Postulates of Dalton Atomic Theory

Explanation of Laws of Chemical Combination: Dalton’s Atomic Theory:

Dalton’s atomic theory provided an explanation for the law of conservation of mass and the law of definite proportions. According to Dalton’s atomic theory, all matter (whether an element, a compound a mixture), is composed of small particles, called atoms.

The Main Postulates of Dalton’s Atomic Theory

1.    Every matter is made up of very small particles, called the atoms.

2.    Atoms are indivisible particles which can neither be created nor be destroyed in a chemical reaction.

3.    Atoms of a given element are identical in mass as well as in chemical properties.

4.    Atoms of different elements have different masses and chemical properties.

5.    Atoms combine in the ratio of small whole numbers to form compounds.

6.    The relative numbers and kinds of atoms are constant in a given compound.

Merits of Dalton’s Atomic Theory:

  • This theory explains the laws of chemical combination.
  • Dalton was the first to recognise a workable distinction between the ultimate particle of an element (atom) and that of a compound (molecule).
  • Demerits of Dalton’s Atomic Theory

  • Atom is no longer considered as the smallest indivisible particle. It has been established that it is made up of electrons, protons and neutrons.
  • Atoms of the same element may have slightly different masses (Isotopes).
  • Atoms of different elements may have the same masses (Isobars).
  • Substance made up of the same kind of atoms may have different properties.
  • The ratio in which the different atoms combine to compound may be fixed and integral but may not be simple.
  • Sample Questions
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    Question : 1

    Identify the Main Postulates of Dalton’s Atomic Theory

    (a)  Every matter is made up of very small particles, called the molecules.

    (b)  Atoms are indivisible particles which can be created and destroyed in a chemical reaction. 

    (c)   Atoms of a given element are identical in mass as well as in chemical properties.

    (d)  Atoms of different elements have different masses and chemical properties.

    (e)   Atoms combine in the ratio of small whole numbers to form compounds.

    Right Option : B
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    Question : 2

    According to Dalton's atomic theory, atoms ________________________.

    Right Option : D
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    Question : 3

    Which of the following statements contradicts Dalton's atomic theory ?

    Right Option : B
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