Chemistry

• Relative atomic mass


  The average mass of an atom of an element compared to 1/12 the mass of an atom of carbon-12
• Mass spectrometer


  Gives accurate information about relative isotopic mass and also about the relative abundance of isotopes
• Electron impact ionisation


  Sample is vaporised, electron gun fires high energy electrons at it, causing an electron to be knocked off each particle to produce 1+ ions
• Electrospray ionisation

  Sample is dissolved and pushed through a fine needle with a high voltage tip, each particle gains an H+ ion and turns into a gas
• First ionisation energy

  The energy required to remove the most loosely held electron from one mole of neutral gaseous atoms to produce 1 mole of gaseous ions each with a charge of 1+
• TOF spectrometry

  1. Ionisation

  2. Acceleration

  3. Ion drift

  4. Ion detection
• Acceleration

  Positively charged ions are accelerated by an electric field so that they have the same kinetic energy
• Ion drift

  Ions enter a region with no electric field so they drift through it. Lighter ions drift faster
• Ion detection

  Negatively charged plates detects charged particles and a mass spectrum is produced
• Relative molecular mass

  The average mass of one molecule of an element or compound compared to 1/12th the mass of an atom of carbon-12
• Co-ordinate bond (dative covalent)


  Bond contains a shared pair of electrons with both electrons supplied by one atom
• Dipole

  Difference in charge between the two atoms of a covalent bond
• Dipole

  Caused by a shift in electron density in the bond due to the electronegativity difference between the elements
• Electronegativity

  The power of an atom to attract the electron density in a covalent bond towards itself
• Electron pair repulsion

  Repulsion that exists between electron pairs due the negative electrons
• Electrostatic forces


  Strong forces of attraction between oppositely charged ions
• Hydrogen bond

  An interaction between a hydrogen atom and an electronegative atom
• Elements hydrogen bonding occurs with

  • Nitrogen
  • Fluorine
  • Oxygen
• Hydrogen bond

  The slightly positive hydrogen is attracted to the lone pair on the electronegative atom
• Intermolecular forces

  Forces which exist between molecules
• Types of intermolecular forces

  • Van der Waals
  • Dipole-dipole
  • Hydrogen bonds
• Standard enthalpy of combustion

  Enthalpy change when one mole of a substance burns completely in oxygen with all substances in their standard states
• Enthalpy change


  Heat change at constant pressure