The Atom

The Atom

1. Greeks - idea everything is made of small particles

2. John Dalton - Theory of Atoms; atoms can't be created/destroyed

3. JJ Thompson - cathode rays attracted by + plate = discovery of electron - plum pudding model of atom

4. William Crookes - Maltese Cross Exp & Paddle Wheel Exp - radiation from cathode = cathode rays

5. Robert Milikan - Oil Drop Exp = size of charge of electron

6. Ernest Rutherford - Gold Foil Exp = nucleus

   • Most particles hit foil; some deflected - all mass concentrated in tiny nucleus @ centre
   • Bombarded nuclei with alpha particles - release of + charged particles = protons

7. James Chadwick - neutron - beryllium w/alpha particles = particles with no charge = neutrons

8. Atomic No - number of protons in an atom of an element

9. Mass No - sum of protons & neutrons in nucleus

10. Isotopes - atoms with same atomic number, different mass number (diff no of neutrons)

11. Relative Atomic Mass - average of mass no's of isoptopes of an element as they occur naturally taking in abundances and compared to 1/12th mass of carbon-12 isotope

    • Calculations = find sum of products and divide by 100

12. Mass Spectrometer

    • Uses - work out relative atomic mass
      • identifying compounds eg drug testing
      • measure abundancies of isotopes
    • Principal - + charged ions are separated based on their relative masses in magnetic field
    • Processes - Vaporisation, Ionisation, Acceleration, Seperation, Detection
      • V - sample changed to gas, chamber evacuated, solids heated
      • I - electron gun bombards sample w/high energy electrons - changes to + charged ions
      • A - + ions accelerated at high speeds by electric field
      • S - magnetic field deflects ions beam - particles separated based on mass
      • D - ions electronically detected - detects no. of each particle hitting it - turned into mass spectrum