Chemistry
State the main postulates of Dalton's atomic theory. How does the modern atomic theory contradict and correlate with Dalton's atomic theory.
Answer
Postulates of Dalton's Atomic Theory:
- Matter consist of small indivisible particles called atoms.
- Atoms are neither created nor destroyed.
- Atoms of the same element are alike in every aspect and differ from atoms of all other elements.
- Atoms combine with other atoms in simple whole number ratio's forming compound atoms or molecules.
- An atom is the smallest unit of matter which takes part in a chemical reaction and all chemical changes result from separation or combination of atoms.
Contradictions with Modern atomic theory:
| Dalton's atomic theory | Modern atomic theory |
|---|---|
| Atoms are indivisible and indestructible. | Atoms are divisible and destructible. |
| An atom is the smallest indivisible particle of an element | Atoms are divisible - consisting of subatomic particles like electrons, protons and neutrons. |
| Atoms of the same element are alike in all respects and differ from atoms of other elements. | Atoms of the same element may not be alike in all respects as seen in the case of isotopes which are atoms of the same element having same atomic number but different mass numbers. |
Correlation with Modern atomic theory:
The modern atomic theory however correlates with Dalton's atomic theory in the fact that atoms are the smallest unit of matter taking part in a chemical reaction and in a given compound the relative number and kind of atoms is a constant.
Related Questions
Explain in brief the experimental proofs which led to the discovery of –
(i) Electrons
(ii) Protons
(iii) atomic nucleus
(iv) neutrons.
Represent each of the following :
(i) a proton 'p'
(ii) an electron 'e'
(iii) a neutron 'n'
in terms of it's symbols showing the subscript and superscript values.
State in brief the drawbacks of Rutherford's atomic model correlating them with the postulates of Bohr's atomic model.
What is meant by the terms :
(i) subatomic particles,
(ii) nucleus,
(iii) orbits,
(iv) atomic number
(v) mass number with reference to an atom.