History of the atom

• Before discovering neutron, protons and electrons scientists tried to classify elements by arranging them in order of atomic weights
• Atomic weight


  What we now call relative atomic mass
• Early periodic tables were incomplete and had missing elements and so some elements were placed in groups that were not similar to them
• Dmitri Mendeleev


  A Russian scientist
• Mendeleev published his first periodic table


  1869
• Mendeleev's method for creating the periodic table

  1. Ordered the elements by the increase of their atomic weight

  2. Thought about their properties and compounds

  3. Had gaps due to unknown elements

  4. Lined up elements with similar chemical properties in groups
• Mendeleev predicted the existence of 'eka-silicon' just by looking at the properties of the elements next to the gap
• Which two elements were reversed in Mendeleev's table?

  Iodine and Tellurium
• John Dalton was a chemist in the 1800's. He performed experiments and studied gas pressure to test the theory of atoms.
• John Dalton's theory of the atom: All substances are made up of atoms, All atoms from the same element have the same mass, Atoms join together to form compounds
• Group 0 didn't exist before Dmitri Mendeleev's periodic table as the noble gases weren't discovered.
• Who invented the Alpha particle scattering experiment?

  Geiger and Marsden