Wilson book 1

• Electrons attracted to nucleus due to electrostatic forces
• Protons are held together by a strong nuclear force, stronger than electrostatic. Therefore it overcomes the repulsion between protons, but only acts over very short distances (i.e. within the nucleus)
• Relative Atomic Mass


  Average mass of atom of an element
• Relative Atomic Mass is 12 for one atom of carbon-12
• Chemical properties remain the same as there is still the same electron configuration, however isotopes have different physical properties as they have a different number of neutrons, therefore affecting the mass.
• Ar


  Relative Atomic Mass
• Ar = (% isotope 1 x mass isotope 1) + (% isotope 2 x mass isotope 2) / total abundance
• Mass Spectrometry


  An instrumental method of analysis that can be used to find: 1) the abundance and mass of each isotope of an element, 2) the Mr of particular compounds, 3) determination of Ar.
• Mass Spectrometry


  1. Ionising sample

  2. Acceleration

  3. Separating ions in a flight tube

  4. Detection where a mass spectra is produced
• Time of Flight (TOF) Mass Spectrometer


  One type of mass spectrometer that uses the 4 stages of mass spectrometry
• Vacuum is used to prevent the ions produced from colliding with air
• Ionisation methods


  • Electron impact - sample vapourised, high energy beam of electrons ionise sample
  • Electrospray ionisation - sample divided into fine mist, tip of needle held at high voltage to give sample a proton
• Acceleration


  Ions accessed by an electric field, particles with lower mass experience greater acceleration
• Ion drift


  Ions travel through a vacuum in the negatively charged plate, lighter ions reach the detector first
• Detection


  Ions with shorter time of flight reach the detector first, flow of current indicates the abundance of each ion
• m/z ratio


  Relative mass of an ion (m) divided by its charge (z)
• The molecular ion peak has the highest m/z value (furthest to the right) and is often smaller than other peaks due to fragmentation
• The tallest peak in the mass spectrum is called the base peak
• Ethanol


  • CH3CH2OH
• Fragmentation of ethanol produces peaks at lower m/z values
• Electron configuration


  The idea of an electron moving as a charged particle at a fixed energy level cannot be explained mathematically. The solution was to consider electrons having wave or particle duality, described by quantum mechanics.
• Atomic orbitals


  • The region of space in which there is a 90-95% chance of finding an electron
  • There are s, p, d, and f orbitals which differ in shape
• Pauli exclusion principle


  Only 2 electrons can occupy a single orbital, and they must have opposite spin
• Electron spin


  A quantum property of an electron, a form of angular momentum
• Electron shells


  • 1
  • 2
  • 3
  • etc.
• Maximum number of electrons in a shell

  2n^2, where n is the shell number
• Electron subshells

  • s
  • p
  • d
  • f
• Hund's rule - atomic orbitals of the same energy fill up singly before starting to pair up with opposite spin
• Exceptions to the expected electron configuration occur in Cu and Cr due to the stability of half-filled s orbitals and fully occupied d orbitals
• The higher the ionisation energy, the more difficult it is to remove an electron
• Factors affecting ionisation energy: nuclear charge, distance from nucleus, shielding by inner electrons
• Across a period

  Ionisation energy increases
• Down a group

  Ionisation energy decreases
• Successive ionisation energies are always higher than the previous one, as electrons are being removed from a more positively charged species
• Trends in ionisation energy can be used to predict the group of an unknown element
• Other periodic properties include atomic radius, electronegativity, and melting/boiling point
• Overall trend in 1st IE

  • Gradually decreases
  • More shielding which cancels out a bigger effective nuclear charge (more protons)
  • Atoms get bigger (more shells)
  • Outer electrons are further from the nucleus (weaker nuclear attraction for outer electrons)
  • Less energy required + easier to remove the electrons
• Successive IEs are always more different and greater than the previous one (more energy required) because electrons are being removed from a more species
• Large increases in successive IEs can occur when there is a change in electron shielding (greater nuclear attraction for remaining electrons)
• Increases in successive IEs can be used to predict the group of an unknown element