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• Lithium (Li) atom

  Atomic Number: 3, Mass Number: 7, Atomic Symbol: Li
• Atomic Number (Z)


  Number of protons in the nucleus
• Mass Number (A)


  Total number of protons and neutrons in the atom
• Number of neutrons


  A - Z
• Isotopes


  Atoms with the same number of protons, but different numbers of neutrons
• Relative isotopic mass


  Mass of one atom of an isotope compared to one twelfth of the mass of one atom of carbon-12
• Relative atomic mass


  Weighted mean mass of one atom compared to one twelfth of the mass of one atom of carbon-12
• Relative molecular mass


  Average mass of a molecule compared to one twelfth of the mass of one atom of carbon-12
• Isotopes have similar chemical properties because they have the same electronic structure
• Isotopes may have slightly varying physical properties because they have different masses
• Mass Spectrometer


  • Can determine all the isotopes present in a sample of an element and to therefore identify elements
• Mass spectra for Cl2 and Br2


  • Cl has two isotopes Cl35 (75%) and Cl37(25%)
  • Br has two isotopes Br79 (50%) and Br81(50%)
• m/z (mass/charge ratio)


  Measured by the mass spectrometer for each isotope
• Molecular ion


  The peak with the largest m/z, due to the complete molecule and equal to the Mr of the molecule
• Uses of mass spectrometers


  • Identifying elements on other planets
  • Drug testing in sport
  • Quality control in pharmaceutical industry
  • Radioactive dating
• First ionisation energy


  The energy required when one mole of gaseous atoms forms one mole of gaseous ions with a single positive charge
• Second ionisation energy


  The energy required when one mole of gaseous ions with a single positive charge forms one mole of gaseous ions with a double positive charge
• Factors affecting ionisation energy


  • Attraction of the nucleus
  • Distance of the electrons from the nucleus
  • Shielding of the attraction of the nucleus
• Successive ionisation energies are always larger
• When the first electron is removed


  A positive ion is formed, increasing the attraction on the remaining electrons and requiring more energy to remove the next electron
• The pattern in the first ionisation energy gives useful information about electronic structure
• Helium has the largest first ionisation energy
• First ionisation energies decrease down a group
• There is a general increase in first ionisation energy across a period
• Sodium has a much lower first ionisation energy than neon
• There is a small drop in first ionisation energy from magnesium to aluminium
• Electrons are found in shells
• Electrons further from the nucleus are more shielded so the attraction of the nucleus becomes smaller
• Phosphorus 1s2 2s2 2p6 3s2 3p3, Sulfur 1s2 2s2 2p6 3s2 3p4
• Patterns in the second ionisation energy


  • If the graph of second ionisation or each successive element is plotted then a similar pattern to the first ionisation energy is observed but all the elements will have shifted one to the left
  • The group 1 elements are now at the peaks of the graph
  • Lithium would now have the second largest ionisation of all elements as its second electron would be removed from the first 1s shell closest to the nucleus and has no shielding effects from inner shells. Li has a bigger second ionisation energy than He as it has more protons.
• Principle energy levels


  • 1
  • 2
  • 3
  • 4
• Sub energy levels


  • s
  • p
  • d
  • f
• Orbitals


  • Represent the mathematical probabilities of finding an electron at any point within certain spatial distributions around the nucleus
  • Each orbital has its own approximate, three dimensional shape

  
• Atoms fill up the sub shells in order of increasing energy (note 3d is higher in energy than 4s and so gets filled after the 4s)
• Using spin diagrams


  • An arrow is one electron
  • The arrows going in the opposite direction represents the different spins of the electrons in the orbital
  • Box represents one orbital
• When filling up sub levels with several orbitals, fill each orbital singly before starting to pair up the electrons
• Blocks of the periodic table


  • s block
  • p block
  • d block

  
• Positive ion formation


  Electrons are lost
• Negative ion formation


  Electrons are gained
• Atomic radius decreases as you move from left to right across a period, because the increased number of protons create more positive charge attraction for electrons which are in the same shell with similar shielding