Atom model/history

• J.J Thomson discovered electrons and modelled the atom as the ‘ plum pudding ‘ . This concluded that atoms were a sphere of positive charge with negatively charged electrons mixed in.
• Rutherford discovered alpha particles could bounce of atoms, concluding that atoms had a nucleus that contained protons.
• Bohr discovered that electrons orbit the nucleus.
• Chadwick discovered some particles have no charge and are called neutrons
• Relative mass = number of protons + number of neutrons
• John Newlands periodic table was ordered by mass and was incomplete
• Mendeleev added groups to the periodic table for undiscovered elements. He predicted the properties and masses of undiscovered elements
• Group 0 are noble gases. They are unreactive as they have a full outer shell.
• Noble gases have low densities and low boiling points. They increase as you move down the group due to the increase in relative atomic mass
• Group 7 are called halogens
• Halogens are very reactive as they have 7 outer electrons. As you move down the group, they decrease in reactivity because the distance from the nucleus increases
• Describe the features of transition metals

  • Not very reactive
  • Used as catalysts
  • Conducts electricity in solid and liquid states
  • High melting points