Atomic Stucture

Atomic Stucture

1. Ions

   • Ions have different numbers of protons and electrons
     • Ions formed by gaining or losing electrons from the atom
       • Positive ions have lost electrons
         • Negative ions have gained electrons
           • Negative Ions repel

2. Isotopes

   • Same element with different numbers of neutrons
   • Number and arrangement of electorns decide the chemical properties of an element
     • Isotopes have the same electrons / config so same chemical porperties
       • Slightly different physical properties due to different mass of atom

3. ToF Mass Spectrometer

   • Ionisation
     • Electron Impact
       • Sample is vaporised
         • High energy electrons fired at sample from an electron gun
           • Forms +1 ions that are attracted to -ve plate
     • Electrospray
       • Sample dissolved in volatile solvent
         • Injected through fine needle
           • Tip of needle attached to +ve end of high-voltage supply
             • Forms +1 ions by gaining a proton from solvent
   • Detection
     • Positive ions discharged
       • By gaining electrons when hit detector
         • Generates a current from the movement of electrons
           • Size of current indicates number of ions hitting plate
           • Mass spectrum
             • Data used to produce graph
               • mass to charge ratio (m/z) against abundance
                 • used to work out relative atomic mass of element
                   • = mass of isotopes / abundance
             • Greatest m/z value
               • Tells us the relative mass of sample
                 • small signal may be above it
                   • this is due to ions having higher mass on a single atom
                   • Signals below are due to fragmentation of molecular ions
   • Flight Tube
     • Low mass, faster
       • Fastest meets detector first
   • Acceleration
     • +1 ions accelerated using electric field
       • So that they all have the same kinetic energy
         • Velocity depends on mass
           • low mass, faster
   • Instrumental method of analysis
     • Used to find abundance and mass of each isotope of an element
       • This allows us to find its relative atomic mass
       • Used to find relative molecular mass of substances of molecules

4. Electronic Structure

   • Electron shells made up of sub-shells and orbitals
     • Electrons move around nucleus in regions of an atom - shells or energy levels
       • Shells are divided into sub-shells which have slightly different energies
         • Sub-shells have different numbers of orbitals which can each hold 2 electrons
           • Two electrons in each orbital spin in opposite directions due to repulsion
           • 1s^2 - 1 orbital, 2e-
           • 2p^6 - 3 orbitals, 6e-
           • 3d^10 - 5 orbitals, 10e-
           • 4f^14 - 7 orbitals, 14e-
   • Further the shell is from the nucleus, the higher its energy
   • Number of outer shell electrons decide chemical properties
     • Group 1 and 2 easily lose electrons from outershell to from positive ion
       • Group 5, 6 ,7 can gain 1, 2, 3 electrons form negative ions
         • Group 4, 7 share electrons to form covalent bonds
           • Group 0 have filled sub-shells, dont react making them inert
             • Transition metals lose s, d electrons forming positive ions
               • Transition metals are unusual
                 • Copper and Chromium fill their 4s sub shell singly
                   • Energetically more favourable to fill 3d sub shell first
                     • They also lose the 4s electron before 3d when becoming ions
       • Form inert gas configuration

5. Ionisation Energy

   • Ionisation - removal of electrons from atoms or molecule
   • Factors
     • Nuclear Charge
       • more protons in nucleus, stronger the attaction to electrons
     • Shielding
       • More electrons between nucleus and outer electron, less attaction between the two
     • Nucleus Radii
       • Attraction falls off rapidly with distance, larger the radii, less attaction
   • Trends
     • Across any period
       • Increase harder to remove outer electron
         • Across period increasing nuclear charge, more protons
           • Shielding the same across
             • More attaction between the electrons and protons
     • Down a group
       • Extra electron shells
         • Less attraction between positive nucleus and outer electron
           • Furthest electron far away
     • ALM
       • Despite increase in nuclear charge,
         • Outer Al electron in a higher energy sub-shell
           • increase shielding
             • Less energy needed to remove the electron
         • Same shielding, same orbital
           • Phosphorus has 1 fully occupied orbital
             • Repulsion in the electron orbital
     • SLP

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