Dalton's atomic model

October 02, 2018 0 Comments



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 the nature. This curiosity has been the mother of all inventions. There have been many models and theories to predict the same. On such model is Dalton's atomic model. We will learn about Dalton's atomic model and it's postulates in this post. We will also look upon the limitations of Dalton's atomic model. Let's begin



Dalton's atomic model

Democritus was the first man who proposed that matter is made up of particles. He named these particles 'disceret 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.

Sir. John Dalton


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 know look at the basic postulates of Dalton's atomic model 



Postulates of Dalton's atomic model

  • Matter is made of extremely small discrete particles called atoms.
  • Atoms of a particular element are identical in all respects, i.s., they posses same size, same shape, same mass, and similar chemical properties.
  • Atoms of one elements 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 intirely free of limitations. Let us look at the drawbacks of the Dalton's atomic model




Drawbacks of Dalton's atomic model

  • It could not explain the Gay Lussac's law of combining volumes.
  • It could not explain why and how do atoms combine together to form compound atoms.
  • It could not explain the nature of force which hold the atoms together in compound atoms.
  • It could not explain why atoms cannot exist in free State and why compound atoms can exist freely.

As we all know that this model was proposed in the 18th century when there was no well developed instruments to analyse anything deeply (Ex- electron microscope) but in present day there were so many developed instruments are available, so let's a look of present day postition 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 same atomic number but different mass number).
  • Atoms of one elements may be similar to the mass of another element. It's due to the discovery of isobars (Isobars - Elements having same mass number but different atomic number).
  • Atoms is divisible and can be divided into sub atomic 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 molecule.


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