Name: Valencies of Some Common Ions
Uploaded: 2019-07-19
Duration: 4 min 56 s
Description: Ionic compounds are composed of positively charged and negatively charged ions. Do you know what the charges on these ions are called? Let’s find out in this...

Question

State the postulates of Dalton's atomic theory. Is the theory valid at present? Give reasons.

Accepted Answer

The main postulates of Dalton's atomic theory are as follows:
1. Matter is composed of very tiny particles called atoms.

2. Atoms are incapable of being destroyed or created.

3. Atoms of any pure substance can neither be subdivided nor changed into atoms of another element.

4. All atoms of an element are identical in terms of mass, size and other properties.

5. Atoms of one element differ in mass and other characteristics from those of other elements.

6. Chemical combination results in the union of atoms in numerical proportions to form many new substances.

7. The relative number and kinds of atoms are constant in a given compound.

This theory is not valid at present because, according to modern theory, atoms are not indivisible particles, they contain sub-atomic particles such as, protons, neutrons, and electrons, which have their individual mass and charge and another reason is that all atoms of the same element are not identical in all respects, masses, chemical properties etc. because, isotopes of the same element differ in their atomic numbers and physical properties, as they have a same number of protons, but differ in the number of neutrons.

State the postulates of Dalton's atomic theory. Is the theory valid at present? Give reasons.

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