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.

Learn about the fundamental particles of an atom, including electrons, protons, and neutrons, and how they were discovered. Understand the failure of Dalton's atomic theory and the significance of J.J. Thomson's cathode ray experiment.