Dalton's atomic model

It's amazing to think about how life evolved on this planet. Ever, since our existence on this planet, the human brain is curious to understand nature. To know all these aspects of life there are many theories and models are present to predict it. On such a model is Dalton's atomic model. We will learn about Dalton's atomic model and it postulates in this post. We will also look upon the limitations of Dalton's atomic model. Let's begin



Dalton's atomic model

The first man who proposed that matter is made up of particles is Democritus. He named these particles 'discreet particles' meaning indivisible. This was the Democritus atomic theory. Due to the lack of technological setup back
then, scientists have very limited therapy on this.
Almost after fifteen hundred years, John Dalton, an English chemist, suggested that the discrete particles which build up matter are atoms. On the basis of the law of chemical combination and the work of ancients Greek philosopher, he proposed a very important model Dalton's atomic model in the year 1804.




Let us now look at the basic postulates of Dalton's atomic model 


Postulates of Dalton's atomic model

  • The matter is made of extremely small discrete particles called atoms.
  • Atoms of a particular element are identical in all respects, i.s., they possess the same size, same shape, same mass, and similar chemical properties.
  • Atoms of one element differ from the atoms of the other elements in all respects, i.s., the atoms of two elements differ in size, shape, mass and chemical properties.
  • Atoms are indivisible, i.s., they cannot be further subdivided.
  • Atoms are indestructible, i.s., they can neither be created nor can be destroyed.
  • Atom is the unit of a chemical reaction
  • Atoms of different elements combine with each other in a fixed simple, whole number ratio to form compound atoms.



However, this model is not entirely free of limitations. Let us look at the drawbacks of the Dalton's atomic model



Drawbacks of Dalton's atomic model

1)It could not explain the Gay Lussac's law of combining volumes.

2)It could not explain why and how do atoms combine together to form compound atoms.

3)It could not explain the nature of the force which holds the atoms together in compound atoms.

4)It could not explain why atoms cannot exist in free State and why compound atoms can exist freely.

5)Dalton’s Atomic Theory suggested that an atom is the smallest part that takes part in a chemical reaction, but now as we know that many other particles are also present which are much smaller than an atom.


As we all know that this model was proposed in the 18th century when there were no well-developed instruments to analyze anything deeply (Ex- electron microscope) but in the present day there were so many developed instruments are available, so lets a look of the present-day position of Dalton's atomic model.

Source- Wikipedia

Present Day position of Dalton's Atomic Model

  • Atom is the smallest particle of matter which cannot exist in free State.
  • Atoms of a particular element may not be identical. Due to the discovery of isotopes (isotopes - elements having the same atomic number but a different mass number).
  • Atoms of one element may be similar to the mass of another element. It's due to the discovery of isobars (Isobars - Elements having the same mass number but a different atomic number).
  • Atoms are divisible and can be divided into subatomic particles like electrons, protons, and neutrons.
  • Atom is destructible. Due to the Einstein equation E=mcá’¾.
  • Atoms of different elements usually combine together in a fixed, simple, whole number ratio to form a molecule.


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