CBSE Class 11-science Answered

According to Dalton’s atomic theory, all matter, whether an element, a compound or a mixture is composed of small particles called atoms. The postulates of this theory may be stated as follows:

1. All matter is made up of very tiny particles. These particles are called atoms.

2. An atom cannot be divided further i.e., atoms are indivisible.

3. Atoms can neither be created nor destroyed in a chemical reaction.

4. All atoms of an element are identical in all respects, including the mass, chemical properties, etc.

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

6. Atoms of different elements combine in small whole number ratios to form compounds.

7. In a given compound, the relative number and types of atoms are constant.

   
   

   Limitations of Dalton’s atomic theory

   Dalton’s atomic theory suffered from the following drawbacks:

   (i) It failed to explain how and why atoms of different elements combine together to form a new ‘group of atoms’.

   (ii) It failed to explain how atoms of different elements differ from each other i.e the structure of atom was unknown.

   (iii) It failed to explain the nature of the binding forces between different atoms in a molecule.

   (iv) According to Dalton, an atom is indivisible, whereas, it can be divided into sub- atomic particles- electrons, protons and neutrons.

   (v) Atoms of the same element can differ from each other.Example – isotopes (atoms of the same element with different masses)

   (vi) Atoms of different elements can have same masses (isobars).