Atomic structure

Atomic structure

1. Sub-atomic particles

   • Electrons
     • Charge- -1
     • Mass- Neglidgible
     • no. of electrons in shell = 2n^2
   • Nucleons
     • Protons
       • Mass- 1
       • Charge- +1
     • Neutrons
       • Charge- 0
       • Mass- 1

2. Atoms

   • Mass no.- protons+neutrons
   • Atomic no.- protons
   • Isotope- Same no. of protons, different no. of neutrons

3. Mass spectroscopy

   • Vacuum so that ions do not collide with air molecules
   • Gaseous sample
   • Ionisation
     • Beam of electrons knocks out an electron (+ion formed)
       • Sometimes 2 elections knocked out (halves the m/z)
   • Acceleration
     • Positive ions attracted to negatively charged plates
       • The speed they go depends on the mass
         • Some pass through slits in the plate, forming an ion beam
   • Deflection
     • Beam of ions move into magnetic field at right angles to its direction of travel
       • Magnetic field deflects the ions into an arc of a circle
     • Deflection depends on
       • m/z ratio
       • 2+ ions deflected twice as much as 1+ ions with the same mass
       • EMF strength
   • Detection
     • EMF gradually increased so ions of increasing mass enter the detector
       • Ions accept electrons when they strike the detector, so lose charge
         • creates a current that is proportional to the abundance of each ion
   • Results
     • From the strength of the EMF at which an ion hits the detector, a computer works out the m/z ratio of the original ion
       • Mass spectrum produced
         • Isotopes
           • Average relative atomic mass = Σ(abundance x m/z) ÷ overall abundance
         • Molecular ions e.g. Cl2

4. Electron arrangement

   • 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 4d10 4f14
     • Add 4s before 3d
     • Remove 4s before 3d
     • When a full orbital, electron spin =0
     • When in a new sub level, each orbital is singly filled before being doubly filled

5. Electron arrangement and ionisation energy

   • The energy required to remove one mole of electrons from one mole of gaseous atoms
     • Each ionisation requires more energy than the prior one (successive ionisation energies)
       • Depending on how close each ionisation energy is, it shows how many electrons are in a shell

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