1. Atomic Structure

1. Atomic Structure

1. Time of Flight; Mass Spectrometer

   • Ionisation: Solvent is forced through a hollow needle--> connected to +ve terminal of high voltage supply. As spray emerges from needle as tiny droplets, it is +vely charged as it has lost electrons to the +ve charge on the supply.
   • Vacuum: prevent ions that are produced from colliding with molecules in the air
   • A volatile solvent is to be analysed
   • Acceleration: Ions are accelerated using an electric field, so they all have the same kinetic energy. +ve ions are attracted towards a -ve plate; accelerate towards it
   • Ion Drift: Ions enter the drift region via a tiny hole in -vely charged plate, forming a narrow beam that travels down a tube towards a detector. Lighter ions have a faster TOF. Heavier ions have lower TOF.
   • Detection: Ions pick up electrons upon collision with detector plate- current produced,
     • Size of current ∝ abundance of isotope
     • Lighter ions hit detector first- they have higher velocities.
     • Flight times are recorded
       • Mass of individual ions are calculated by how long it took to hit the detector.
   • Used to identify different isotopes that make up an element. Individual ions are detected, so different ions are detected separately because they have different masses.
     • Can measure Relative atomic mass up to 5dp --> high-resolution mass spec
   • Mass spectrum: can calculate Relative atomic mass. RAM= ((m/z * abundance) + (m/z * abundance)) / total abundance
     • Mass spec of molecule: peak on the far right gives m/z of molecular ion- can work out Mr of molecule
     • Low-resolution mass spec: 1dp

2. ELECTRON CONFIGURATION

   • Main energy levels has sub levels s, p, d and f.
     • 1st main level has s sub-level, holding 2 e-. 2nd level has s and p sub-level, holding 8 e-. 3rd has s, p and d sub-level, holding 18 e-.
   • Electron is no longer considered a particle. It is considered as a cloud of negative charge. It takes up a volume in space called its atomic orbital
     • Different atomic orbitals have different energies.
       • Atomic orbitals for each main level have different shapes, which have different energies- sub levels.
         • These shapes represent a volume in space.
         • Sub levels in higher main energy levels, have higher energies. i.e. the 3 p-orbitals in in 2nd level have a lower energy than the 3 p-orbitals in the 3rd main level
         • 2nd atomic level has an s-sub-level and a p-sub-level, which has 3 p-orbitals of equal energy
           • 3rd atomic level has an s-sub-level, a p-sub-level and a d-sub-level, which has 5 d-orbitals of equal energy
         • 4 s-sub-level is of lower energy than 3 d-sub-level.

3. IONISATION ENERGY

   • The patterns of 1st IE across a period provide evidence for electron energy sub-levels
     • Graph of Na IE. Suggests that it has 1 e- easy to remove. 8 e- nearer to nucleus, harder to remove. 2 e- closest to nucleus, very hard to remove as they are nearest to +ve charge of nucleus.
   • Ionisation energy- energy required to remove 1 mole of electrons from a mole of gaseous atoms to form 1 mole of gaseous ion.
     • KJ/mol
     • Only used for the formation of +ve ions
       • Electron affinity is used for formation of -ve ions
   • Removing electrons 1 by 1:
     • 1st e - requires least amount of energy as it is being removed from a neutral atom
       • 2nd e- needs more energy to remove it as it is being removed from a +1 ion.
         • 3rd e- needs even more energy to remove it as it is being removed from a 2+ ion. 3rd e- needs more and so on.
     • The 2nd IE is the sum of the 1st IE and the energy to remove another e- from the ion formed in the first IE.
   • Trend across period
     • Increases across period as nuclear charge increases, it is more difficult to remove the electron, as electron is much more drawn to nucleus with a greater charge. Electrostatic force is much greater on outer e- across period
       • Generally increases
         • Small dip between Mg and Al, and between P and S
           • Outer e- in sulfur p-orbital is paired with another e-. Phosphorus outer e- is not paired. Repulsion between these two e- makes it easier to remove one of them, hence Sulfur has a lower 1st IE
       • Mg to Al IE decreases as less energy is required to remove outer e- from Al, because Al outer e- is in an orbital of higher energy
   • Trends down a group
     • Outer e- is in a main level that gets further away from nucleus
       • Decreases. Even though nuclear charge increases, the outer e- gets further and further away from the +ve nucleus. Inner electrons and energy levels and sub-levels, shield the increase in +ve charge, so electrostatic force 'felt' by the e- in the outer shells is less than the full nuclear charge.

4. ISOTOPES

   • Atoms with the same number of protons but have different numbers of neutrons
   • Different isotopes of the same element react chemically in exactly the same way as they have the same number of electrons
   • Atoms of different isotopes vary in mass number

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