Atomic Theory

• The Ancient Greeks (Democritus)


  Around 400 BC
• Atom


  Tiny discrete particle of matter, from the greek word 'atomos' meaning uncuttable or indivisible
• Democritus suggested that all matter was composed of different types of tiny discrete particles
• The properties of these particles determined the properties of matter
• Isaac Newton


  1704
• Isaac Newton theorised a mechanical universe with small, solid masses in motion
• Isaac Newton began to develop the understanding that atoms (or particles) move, and are not stationary
• Antoine Lavoisier


  1743-1794
• Law of conservation


  Energy can neither be created nor destroyed, but only transferred (moved from A to B) or transformed (changed in form/type)
• Antoine Lavoisier helped trigger the scientific debate on what exactly an atom is
• Antoine Lavoisier identified 33 elements, grouping them into metals and non-metals
• John Dalton


  1808
• John Dalton's theory


  • Matter is composed of extremely small particles called atoms
  • Atoms are indivisible and indestructible
  • Atoms of a given element are identical in size, mass, and chemical properties
  • Atoms of specific elements are different from those of other elements
  • In a chemical reaction, atoms separate, combine, and/or rearrange
• John Dalton developed an early form of the periodic table that consisted of 36 elements in 1808
• John Dalton developed Dalton's model, a model of an atom picturing them to be solid masses
• J.J. Thomson


  1897
• J.J. Thomson discovered that the atom consists of smaller subatomic particles called electrons
• J.J. Thomson's atomic model

  Atoms are similar to plum pudding, with electrons being chunks of plum in positive "goo" or pudding
• J.J. Thomson came up with this idea by conducting a cathode ray tube experiment
• Ernest Rutherford


  1911
• Ernest Rutherford found out the charge of atoms and began the understanding of the interior of the atom
• Ernest Rutherford established that the nucleus was extremely dense, small, and positively charged
• Ernest Rutherford assumed that the electrons were located outside the nucleus, and he also discovered protons
• Ernest Rutherford discovered the nucleus through an experiment where he shot alpha particles at a thin piece of gold foil, observing that the particles occasionally bounced off
• Niels Bohr


  1922
• Niels Bohr's atomic structure theory

  The outer orbit of an atom could hold more electrons than the inner orbit, and electrons didn't spiral into the nucleus, but orbit in different levels
• Niels Bohr developed the Bohr model, also known as the quantum model
• Erwin Schrödinger


  1926
• Erwin Schrödinger formulated a wave equation that accurately calculated the energy levels of electrons in atoms
• Erwin Schrödinger theorised that the behaviour of electrons within atoms could be explained by treating them mathematically as matter waves
• James Chadwick


  1932
• James Chadwick discovered neutrons, particles whose mass was close to that of a proton
• James Chadwick concluded that neutrons can penetrate and split the nuclei of most elements, starting the seed of radioactive theory
• James Chadwick, similar to Rutherford, used alpha particles to discover the neutron