Química S1

• Democritus:

  • 400 BCE in ancient Greece. 
  • First known model of an atom. 
  • Matter could be cut up into smaller and smaller pieces (atomos=indestructible) until a point was reached where it could not be cut up anymore.
  • His experiment was to destroy a rock until it was indivisible.
• John Dalton: 

  • British chemist in 1803. 
  • Mass cannot be created or destroyed.
  • Atomic theory to explain why chemical elements reacted in simple proportions by mass. 
  • Atoms of different elements have different masses.
  • Each chemical element consisted of identical atoms and these atoms could bond together to form chemical compounds.
  • Experiments on gases.
• J. J. Thomson:

  • British physicist in 1897.
  • Discovered the electron.
  • ‘Plum pudding’ model of the atom, in which the electrons were embedded in a sphere of positive charge.
• Hantaro Nagaoka: 

  • Japanese physicist in 1904.
  • Rejected Thomson's theory on the grounds that opposite charges are impenetrable (cannot exist within each other).
  • Alternative model of the atom in which a positively charged centre is surrounded by a number of orbiting electrons, similar to Saturn and its rings.
  • Rejected, even by Nagaoka himself.
• Ernest Rutherford:

  • New Zealand physicist in 1909, Thomson’s student.
  • Demonstrated atom is largely empty space.
  • Gold foil experiment.
• Niels Bohr:

  • Danish physicist in 1914.
  • Electrons can only exist in certain fixed energy levels and can transition between them by absorbing or emitting exact amounts of energy.
• Atoms: The smallest particle of an element that retains the properties of said element.
• Matter: A substance that has both mass and volume; typically classified as solid, liquid or gas.
• Pure substances: Consist of only one type of substance and have a fixed composition.
• Elements: The simplest substances composed of only one type of atom and cannot be broken down into simpler substances by chemical means.