Atomic structure

• Subatomic particle: Relative charge: Relative mass

  Proton: +1: 1

  Neutron: 0: 1

  Electron: -1: 1/2000
• Mass no.?


  no. protons and neutrons in nucleus
• Atomic no.?


  no. protons in nucleus.
• What are ions?


  Have a dif no. electrons and protons.
• Define an isotope?


  Elements with same no. protons dif no. neutrons.
• John Dalton?


  Atoms are spheres.
• JJ Thompson?


  Discovered the electron.

  Plum pudding model.

  Positive ball charge negative electrons embedded
• Rutherford?


  Discovered the nucleus that was small and positively charged.

  Concluded atom was mainly empty space made up of negative cloud.

  Positive alpha particles fired at gold foil, most went through, small no. deflected back.
• Bohr


  Electrons were in fixed shells.

  When electromagnetic radiation is absorbed/emitted electrons move between shells.
• TOF spectrometer?


  Sample is vaporised so it can travel through.

  Electrospray ionisation- sample is dissolved in volatile solvent and injected by high voltaged needle into mass spec, gaining a proton. (higher mr method)

  Electron impact- Electron gun fires electrons at sample knocking off 1 electron. (lower mr method)

  Gaseous positively charged sample are produced.

  Positive ions are passed through electric field.

  Particles drift through with same kinetic energy.

  Ions detected as electric current is produced when they hit negatively charged plate, collecting an electron.
• Relative atomic mass?


  Average mass of an atom of an element compared to 1/12 mass of a single carbon 12 atom.
• Relative molecular mass?


  Average mass of a molecule compared to 1/12 mass of a single carbon 12 atom.
• Isotopic mass?


  Average mass of an isotope of an element compared to 1/12 mass of a single carbon 12 atom.
• Molecular ion peak?


  Last peak on mass spectrum is the molecular ion peak.

  It is the same as the relative molecular mass of the molecule.
• Why do we fill orbitals singly first?

  Due to electron repulsion.
• Define ionisation energy?


  Energy required to remove 1 mole of electrons from 1 mole of gaseous atoms.
• KE

  KE= 1/2 m v^2
• velocity=

  v= square root of 2KE/m
• Time=

  t= d/v
• Time=

  t= d x square root of m/2KE
• Distance=

  d= t x square root of m/2KE
• How are ions detected in TOF spectrometer?

  Ions hit the negatively charged plate and gain an electron, producing a current which is proportional to the abundance
• What s block metal has the highest 1st ionisation energy?

  Beryllium
• Why is calciums 2nd ionisation energy lower than potassium?

  As potassiums electron is being removed from 3p orbital which is closer to the nucleus compared to calcium in the 4s1 orbital which has more shielding.
• Mg has ar 24.3. 25Mg atoms make up 10% of a sample of Mg.

  Workout the abundance of Mg24 and Mg26 in the sample?


  2430= 250 + 24x - 26x + 2340

  2430= 250 + 2340 - 2x

  2590-2430= 160

  2x=160

  x=80

  24= 80

  26= 10
• What would cause the relative atomic mass of a sample to be different from the atomic mass in the periodic table?

  Other isotopes present.
• How are ions formed in the TOF spectrometer?

  High voltage is applied to polar solvent causing sample to gain a proton.

  Or sample is bombarded by high energy electrons, losing an electron.
• Why is it necessary to ionise molecules in a TOF spectrometer?

  Ions will interact and be accelerated by an electric field.

  Only ions create a current when hitting the detector.
• What 2 measurements are recorded for each isotope in a TOF spectrometer?

  m/z value and abundance.
• Why do isotopes of an element have the same chemical properties?

  Same electron configuration.
• why is the ionisation energy of every element endothermic?

  Energy is needed to overcome the attraction between the nucleus and electrons
• How does the detector measure abundance?

  Ions hit detector causing a current as they accept an electron.

  Larger current produced= greater abundance.
• Would you expect the chemical reactions of nitrogen compounds to differ?

  No as same no. of electrons.
• Define the 1st ionisation energy?

  Energy required to remove 1 mole of electrons from 1 mole of atoms in the gaseous states.
• Why must a TOF sample be ionised?

  To accelerate the ions.

  To deflect the ions.
• Which letter represents the atomic no.?

  Z
• What does the atomic no. mean?

  no. protons in an atom
• What letter represents mass no?

  A
• How is mass no. calculated?

  No. protons + no. neutrons
• Define relative atomic mass?

  Average mass of an atom of an element compared to 1/12 the mass of a single C-12 atom