Atomic Structure

Atomic Structure

1. PEN

   • Proton
     • Charge = +1
     • Relative mass = 1
   • Electron
     • Charge = -1
     • Relative mass = 0
   • Neutron
     • No charge
     • Relative mass = 1
   • Mass number = proton + neutrons
   • In atom P=E
   • Isotope
     • Different number of neutrons
       • same proton number
     • Chemical properties depend on electrons
       • Electrons arranged same in isotope so same chemical properties
       • Physicals properties differ slightly because mass changes

2. Mass Spectrometer

   • VIADD
     • Vapourisation
     • Ionisation
       • Electron gun fires high energy electrons
         • But use minimum as want least 2+ ions
       • He(g) --> He+ (g) + e-
         • Some 2+ ions created Mg+(g) + e- --> Mg2+ (g) +2e-
     • Acceleration
       • Negative plates attract +ions which accelerates
     • Deflection
       • Electromagnet produces variable magnetic field
       • Amount deflected depends on m/z
         • mass/charge
           • 24Na+ and 48Ti2+
             • Same m/z ratio 48/2 and 24/1 = 24
               • So deflected by same amount
         • Larger m/z the smaller the deflection
     • Detection
       • Tiny current is produced as ion takes electron from negative plante
         • This is then amplified and sent to computer
           • More currents = higher peak
             • current depends on number of ions
   • m/z on x axis Abundance (usually %) on y
     • From graph can calculate relative atomic mass (Ar)
       • Ar=((% x m/z) + (% x m/z) +.....)/total %
       • Ar = average mass of one atom of an element / 1/12 the mass of one carbon-12 atom
         • Mr = average mass of one molecule/ 1/12 the mass of one carbon-12 atom

3. Electronic configuration

   • Orbitals
     • 1s 2s 2p 3s 3p
       • 4s filled befoe 3d
       • electrons are paired with opposite spin
         • with p and greater orbitals electrons remain unpaired filling empty orbitals first but with parallel spin
     • Examples
       • Na 1s2 2s2 2p6 3s1
       • Ti 1s2 2s2 2p6 3s2 3p6 3d2 4s2
       • Exceptions
         • Cr 1s2 2s2 2p6 3s2 3p6 3d5 4s1
         • Cu 1s2 2s2 2p6 3s2 3p6 3d10 4s1
   • Ionisation Energies
     • Increases Across period 3
       • Proton number increase
       • Shielding stays the same
       • Atoms become smaller as you go across
       • Exceptions (Decreases)
         • Aluminium - further from nucleus as it is first element with 3p electron
         • Sulfur - first paired 3p electron so decrease due to electron-electron repulsion
     • Decreases down Group 2
       • More shielding as you go down (offsets proton increases)
       • Further from nucleus
     • Second ionisation energy always higher
       • less shielding
       • lost from ion
         • Ion is smaller