atomic structure/periodic table

• what does the nucleus contain?

  protons and neutrons
• what is the charge of the nucleus?


  positive
• what is the heaviest part of an atom?

  the nucleus
• what is the charge of electrons?


  negative
• what is the charge of protons?


  positive
• what is the charge of neutrons?


  neutral
• what is the relative mass of a proton?


  1
• what is the relative mass of a neutron?


  1
• what is the relative mass of an electron?


  almost nothing
• number of protons=number of electrons
• mass number= protons + neutrons
• atomic number= protons
• number of neutrons= atomic mass - atomic number
• isotope


  when atoms of the same element have the same number of protons but different number of neutrons
• isotopes have the same atomic number but different mass number
• relative atomic mass (Ar)


  = sum of (isotope abundance x isotope mass number) / sum of abundance of all the isotopes
• compouns

  elements are chemically bonded
• mixtures


  elements not chemically bonded
• what are the ways to seperate a mixture?

  • filtration
  • crystallisation
  • simple distillation
  • fractional distillation
  • chromatography
• filtration


  seperates insoluble liquids from liquids
• insoluble


  solid cannot be dissolved in the liquid
• methods for soluble:

  evaporation and crystallisation
• why should pencils and not pens be used in paper chromatography?


  because pencil marks are insoluble and won't dissolve in the solvent
• distillation


  used to separate mixtures containing liquids
• simple distillation

  used when liquids have different boiling points
• fractional distillation

  used when liquids have similar boiling points
• John Dalton

  described atoms as solid spheres
• 1897- JJ Thomson

  • created plum pudding model
  • discovered electrons
• plum pudding model


  ball of positive charges with electrons stuck in it with an overall neutral charge
• 1909 - Ernest Rutherford


  conducted alpha particle scattering experiment
• alpha particle scattering experiment


  fired positively charged alpha particles at a very thin sheet of gold
• results of the APSE

  • most particles went through the gold sheet
  • small number deflected backwards
  • proved plum pudding wrong
• Rutherford


  created the nuclear model - tiny positively charged nucleus in the centre where most of the mass is concentrated, a 'cloud' of negative electrons surround the nucleus so most of the atom is empty space
• Rutherford's theory:


  when alpha particles came near the concentrated positive charge of the nucleus, they were deflected. if fired directly at the nucleus, they deflected backwards
• Bohr


  his nuclear model suggested all the electrons were contained in shells
• Bohr's suggestion:


  electrons orbit the nucleus in fixed shells at a fixed distance from the nucleus
• order of discovery of subatomic particles

  1. electron
  2. proton
  3. neutron
• James Chadwick


  discovered neutrons
• the electronic shells closest to the nucleus have the lowest energy levels
• noble gases were missed out on Mendeleev's periodic table