Structure of Atom

  • Atoms are the basic building blocks of matter.
  • Different kinds of matter exist because there are different kinds of atoms present in them.

Charged Particles in Matter

  • Whenever we rub two objects together, they become electrically charged. This is because atoms contain charged particles in them. Therefore, atoms can be divided further into particles i.e proton, electron and neutron.

Protons were discovered by Ernest Rutherford, in his famous gold foil experiment.

Electrons were discovered by J.J. Thomson, in his cathode ray tube experiment.

Neutrons were discovered by James Chadwick.

  • Atoms consist of protons and electrons in a balanced proportion.
  • Protons exist in the interiors of the atom and electrons exist in the exteriors of the atom. Therefore, electrons can be removed from an atom.

Failure of Dalton’s Atomic Theory

The postulates of the atomic theory by John Dalton

  • The matter is made up of tiny particles called Atoms that cannot be divided.
  • Atoms are never formed or destroyed during a chemical reaction. 
  • Atoms of an element exhibit same nature. They have the same size, mass, and character.
  • Atoms of different elements exhibit variant nature. They do not have same characteristics.
  • Atoms form compounds by combining in a ratio of whole numbers.
  • A compound contains a constant number and kinds of atoms

Dalton suggested that atoms can neither be created nor destroyed and are indivisible. But the discovery of electrons and protons in atoms lead to failure of this aspect of Dalton’s theory.