SC3

• History of the Atom:

  1. Dalton - solid sphere
  2. Plum Pudding - electrons in a positive sphere
  3. Rutherford - gold foil experiment showed the nucleus and electrons moving around randomly
  4. Bohr - current model
• An atom is a nucleus containing neutrons and protons, surrounded by electrons in shells
• Proton - positively charged with a relative mass of 1

  Neutron - no charge and has a relative mass of 1

  Electron - negatively charged and has an negligible atomic mass
• Atoms are neutral as they have the same number of protons and electrons to cancel out their charges.

  Most of the mass is concentrated in the nucleus
• Mass Number - total number of protons and neutrons

  Atomic Number - total number of protons

  All atoms of the same element have the same number of protons in the nucleus
• Isotopes - atoms with the same number of protons but a different number of neutrons
• Relative Atomic Mass - the average mass of one atom of an element compared to 1/12th of the mass of a carbon-12 atom

  • may not be whole numbers as it includes isotopes