Atomic Structure

• What type of force exists between protons and electrons in an atom?

  electrostatic
• What does the number electrons in the outer shell determine?


  Chemical Properties

  how it reacts

  what element it is
• Relative Atomic Mass (Ar)


  the average mass of 1 atom of an element relative to 1/12 the mass of 1 atom of Carbon-12
• Equation for the relative atomic mass

  Ar= ∑ (isotope mass number x % abundance) / ∑ % isotope abundance
• Why do isotopes of the same element have identical chemical properties?

  they have the same number of electrons
• What does Time of Flight determine?

  relative isotopic masses and relative abundances
• How does Time of Flight work?

  works by forming ions then separating them according to their mass:charge ratio
• What are the 4 stages of Time of Flight?

  Ionisation

  Acceleration

  Ion Drift

  Detection
• What are the two types of Ionistion in TOF mass spec?

  Electron Impact ionisation

  Electrospray ionisation
• What is Electron Impact Ionisation?


  samples with low molecular mass

  vaporised, high energy electron fired at sample using electron gun, one electron is knocked off each atom forming a positive ion
• What is the equation for electron impact ionisation?


  X(g) -> X+(g) + e-
• What is Electrospray Ionisation?

  sample with high molecular mass

  sample dissolved in volatile solvent, injected using fine needle at high voltage, particles gain a proton, solvent evaporated leaving positive ions
• What is the equation for electrospray ionisation?


  X(g) + H+ -> XH+(g)
• What is acceleration in TOF mass spec?


  ions accelerated using electric field all have the same kinetic energy but different velocity as they have different masses
• What is Ion Drift in TOF mass spec?


  ions with different masses have a different time of flight
• What is Detection in TOF mass spec?


  negatively charged plate, current is produced when ion hit the plate as electrons are transferred from the negatively charged plate to the positive ions
• What is the equation for Kinetic Energy?

  $KE=$$1/2mv^2$
• What is the equation involving time, distance traveled and velocity?

  $t=$$d/v$
• What are the excpetions to the rule: the 4s orbital has a lower energy than the 3d orbital

  Chromium (Cr): [Ar] 3d5 4s1

  Copper (Cu): [Ar] 3d10 4s1
• What is the definition for first ionisation energy?


  the energy needed to remove one electron from each atoms of an element in one mole of gaseous atoms
• What is the formula for first ionisation energy?

  X(g) -> X+(g) + e-
• What is the definition for second ionisation energy?

  the energy needed to remove one electron from each ion of an element in one mole of gaseous 1+ ions
• What is the equation for second ionisation energy?

  X+(g) -> X2+(g) + e-
• What factors affect ionisation energy?

  PADS

  Proton number

  Attaction between positive nucleus and valence shell electrons

  Distance (atomic radius)

  Shielding
• What is the trend in Ionisation Energy across a Period?


  Higher proton number

  Smaller atomic radius

  Shielding is constant

  Greater attraction of positive nucleus and outer electrons

  Therefore, increasing in Ionisation Energy across a period
• What is the trend in Ionisation Energy going down a Group?


  Larger atomic radius

  Increase in Shielding

  Less attraction of the positive nucleus to outer electrons

  Therefore, ionisation energy decreases down a group
• How does ionisation energy change between Group 2 and 3?


  Dip in 1st Ionisation Energy

  Electron in p orbital is easier to remove as the orbital has a slightly higher energy than s orbital so needs less energy to remove an electron
• How does ionisation energy change between Group 5 and 6?


  Dip in first ionisation energy

  In group 5, p subshell has one electron in each orbital, no repulsion

  In group 6, p subshell has one orbital with 2 electrons, the electrons in the same orbital experience electron repulsion. So less energy is needed to remove the outer electron