atoms

• The plum pudding model was invented by J.J. Thomson
• The plum pudding model depicted a large ball of positive charge with electrons embedded throughout.
• John Dalton stated that atoms are tiny, solid balls like billiard balls.
• John Dalton's theory started

  • Atoms of one element are all the same
  • Atoms of different elements are different, and can make compounds
• The gold leaf experiment/alpha particle scattering was created by Ernest Rutherford
• Rutherford's gold leaf experiment showed that atoms must have a positive charge somewhere and most of the atom is empty space.
• The gold leaf experiment demonstrated that the majority of the alpha particles got through the gold leaf, however some bounced back or deflected.
• Neils Bohr suggested electrons move around in specific layers or 'shells'.
• In 1913, Neils Bohr stated that every atom has a specific number of electron shells.
• James Chadwick discovered a neutral substance in the nucleus with the protons. This was the first mention of neutrons.
• The modern atom has outer shells, containing electrons.
• The first outer shell contains a maximum of 2 electrons
• The second and third outer shells can contain up to 8 electrons
• The charge of a proton is +1
• The charge of an electron is -1
• The charge of a neutron is 0
• A proton's relative mass is 1
• A neutron's relative mass is 1
• The relative mass of an electron is very small, or 1/1836
• The atomic number is the number of protons or electrons within an element
• The relative atomic mass is the sum of protons + neutrons within an element
• An isotope is when an element has the same proton number but different neutron numbers.
• An ion is an atom or group of atoms with a positive or negative charge, due to loss or gain of electrons
• To work out the protons or electrons within an element, look at the atomic number of the element
• To work out the neutrons within an element, take away the atomic number from the relative atomic mass