Atomic Structure

Structure of Atom

• The discovery of electrons and protons inside the atom led to the failure of Dalton's atomic theory.
• An atom consists of three fundamental particles: electrons, protons, and neutrons.

Discovery of Electron

• J.J. Thomson discovered electrons in 1897 through a cathode ray experiment.
• In the experiment, a stream of negatively charged particles (electrons) was observed coming out from the cathode towards the anode.

Discovery of Proton

• Ernest Goldstein discovered protons in 1886 through an experiment with a gas discharge tube.
• He observed that the anode emitted positive particles, which he named as Canal Rays, leading to the discovery of protons.

Discovery of Neutron

• J. Chadwick discovered neutrons in 1932.
• Neutrons are present in the nucleus of all atoms.

Thomson's Model of Atom

• Joseph James Thomson proposed the Thomson's model of an atom in 1897.
• The model states that an atom is a uniform sphere of positive charges (protons) and negative charges (electrons).
• The atom as a whole is electrically neutral due to equal magnitude of positive and negative charges.
• This model is also known as the water melon model, plum pudding model, and apple pie model.
• The model failed to explain the arrangement of protons and electrons in the atom.

Rutherford's Model of Atom

• Ernest Rutherford proposed the Rutherford's model of an atom in 1909.
• The model is based on an experiment where alpha particles were bombarded onto a thin gold foil.
• Most alpha particles passed through the foil without any hindrance.
• Some alpha particles deflected from their original path at a noticeable angle.
• Very few alpha particles bounced back from their original path.