ATOM: A LOOK INSIDE

• Atom


  Fundamental or basic unit of matter that cannot be further divided
• Democritus' theory of atoms


  • All matter consists of atoms
  • Atoms are bits of matter too small to be seen
  • There is an empty space between atoms
  • Atoms are completely solid
  • Atoms have no internal structure
  • Each atom (of a different substance) is different in size, weight and shape
• Dalton's Atomic Theory


  • An atom is an indivisible, uniformly dense, solid sphere (the smallest form of matter)
  • All atoms of a given element have the same unique set of properties
  • A chemical reaction merely consists of a reshuffling of atoms from one set of combinations to another
  • Atoms of different elements always combine in fixed number ratios to produce specific compounds
• Crookes' cathode ray tube experiment


  • Produced a glowing greenish beam
  • Beam was deflected by a magnet
  • Beam cast a shadow behind the anode
  • Beam was made up of negatively charged particles
• Thomson's cathode ray tube experiment


  • Beam bent towards positive electric plate
  • Determined charge to mass ratio (e/m) of the particles
  • Atoms have a negatively charged particle called electrons
  • Positive ion formed from H2 was a single particle with a charge equal to but opposite the electron
• Millikan's oil drop experiment


  • Determined the size of the electric charge of an electron
  • Determined the mass of the electron and the proton
• Becquerel's discovery of radiation


  • Accidentally discovered radiation when doing experiments with uranium
  • Uranium emitted particles that exposed a photographic plate
• Curie couple's discovery of radioactive elements


  • Discovered radioactive elements radium and polonium
  • Discovered 3 types of radiation: alpha, beta, and gamma
• Rutherford's gold foil experiment


  • Alpha particles bounced backwards when fired at gold foil
  • Existence of a very small and extremely dense region called the nucleus in the center of the atom
• Joliot-Curie and Chadwick's discovery of the neutron


  • Neutral radiation emitted when bombarding Be with alpha particles
  • Neutral radiation was formed by a neutral particle called a neutron
• Isotopes


  • Atoms of the same element with different numbers of neutrons
• Isotopes of a given element will differ in their mass numbers while still having the same atomic number
• With the exception of hydrogen, isotopic forms of other elements are denoted by their mass number