SC 8.2

• Discovery of atoms and subatomic particle

  • Atom - originate from a Greek word that means can't be divided or cut
  • 1808 - Dalton's Atomic Theory
  • Introduced by John Dalton
  • Oldest atomic theory
  • Suggest that atoms are smallest particle and cannot be further divided
  • J.J. Thomson found the first sub-atom, the negative-charge electron
  • Thomson's model known as Plum Pudding Model
  • 1911 - Ernest Rutherford who is Thomson's student proposed that all positive charges lie in the centre of an atom and is known as nucleus
  • Electron move surrounding the nucleus
• Discovery of atoms and subatomic particle

  • 1920 - Rutherford found positive-charge particles named as protons
  • 1932 - James Chadwick found neutral particles known as neutron inside the nucleus
  • At present, the fundamental model clearly explains the structure of atom

  
• Atom

  • smallest particle and cannot be further divided
  • Development of science finding particles smaller than atom called subatomic particle
  • proton (Positive charge), electron (negative charge) and neutron (neutral)
  • When numbers of proton in atom = numbers of electron, the atom is neutral
• • When numbers of proton and electron is not equal
  • Proton more than electron - positively charged ions (Cation)
  • Proton less than electron - negatively charged ions (Anion)
• Formative of ions

  • When an atom gains or loses electrons, the atom become a charged particle know as ions
  • Positive ion (cation) - atom loses / donate electron forms a positive ion
  • Negative ion (Anion) - atom gains electron forms a negative ion
  • Metal atom form positive ions while non-metal atom form negative ions