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• Atomic structure model


  Small, dense central nucleus surrounded by orbiting electrons in electron shells
• Nucleus


  • Consists of protons and neutrons
  • Has an overall positive charge
  • Contains almost the entire mass of the atom
• Neutral atom


  Number of electrons is equal to the number of protons due to the relative charges
• Fundamental particles


  • Proton
  • Neutron
  • Electron
• Proton


  Relative charge +1, Relative mass 1
• Neutron


  Relative charge 0, Relative mass 1
• Electron


  Relative charge -1, Relative mass 1/1840
• Maximum number of electrons in a shell

  2n^2 where n is the shell number
• Each electron shell must fill before the next one can hold any electrons
• Mass number (A)


  Sum of protons and neutrons in an atom
• Atomic number (Z)


  Equal to the number of protons in an atom
• Isotopes


  • Hydrogen
  • Deuterium
  • Tritium
• Isotopes


  Atoms of the same element with the same atomic number but different number of neutrons, resulting in a different mass number
• Neutral atoms of isotopes will react chemically in the same way as their proton number and electron configuration is the same
• Different mass numbers of isotopes mean they have different physical properties
• Relative atomic mass (Ar)


  The mean mass of an atom of an element, relative to one twelfth of the mean mass of an atom of the carbon-12 isotope
• Relative isotopic mass


  The isotopic mass of an isotope relative to one twelfth of the mean mass of an atom of the carbon-12 isotope
• Relative molecular mass (Mr)


  The mean mass of a molecule of a compound, relative to one twelfth of the mean mass of an atom of the carbon-12 isotope
• Relative molecular mass can be calculated for a molecule by adding together the separate Ar values of the component elements
• Ions


  Formed when an atom loses or gains electrons, meaning it is no longer neutral and will have an overall charge
• Mass spectrometry


  • Used to identify different isotopes and find the overall relative atomic mass of an element
• Time of Flight (TOF) Mass Spectrometry

  1. Ionisation

  2. Acceleration

  3. Ion Drift

  4. Detection

  5. Analysis
• During the ionisation process, a 2+ charged ion may be produced, which will be affected more by the magnetic field producing a curved path of smaller radius
• The tallest peak on a mass spectrum corresponds to the relative molecular mass of the molecule, this peak is known as the molecular ion peak and is formed from the M+ species
• Spectra produced by the mass spectrometry of chlorine display a characteristic pattern in a 3:1 ratio for Cl+ ions and a 3:6:9 ratio for Cl2+ ions
• Ionisation energy


  The minimum energy required to remove one mole of electrons from one mole of atoms in a gaseous state, measured in kJmol-1
• Successive ionisation energies usually require more energy because as electrons are removed, the electrostatic force of attraction between the positive nucleus and the negative outer electron increases
• Along a Period


  First ionisation energy increases due to a decreasing atomic radius and greater electrostatic forces of attraction
• Down a Group


  First ionisation energy decreases due to an increasing atomic radius and electron shielding which reduces the effect of the electrostatic forces of attraction
• A sudden large increase in successive ionisation energies indicates a change in energy level, because the electron is being removed from an orbital closer to the nucleus so more energy is required
• The first ionisation energy of Aluminium is lower than expected due to a single pair of electrons with opposite spin, resulting in a natural repulsion which reduces the amount of energy needed to be put in to remove the outer electron
• Evidence for electron configurations

  • Emission spectra provide evidence for the existence of quantum shells
  • Successive ionisation energies provide evidence for quantum shells within atoms and suggest the group to which the element belongs
  • The first ionisation energy of successive elements provides evidence for electron subshells
• Electron orbitals


  Electrons are held in clouds of negative charge called orbitals, of types s, p, d and f, each of which can hold up to two electrons with opposite spins and has a different shape
• Each element in the blocks on the Periodic Table has outer electrons in the corresponding orbital type
• Electron configurations


  Scientific ideas on electronic configurations have developed over time as new discoveries are made
• Current, accepted model of electron configurations

  • Based on evidence from emission spectra, successive ionisation energies, and first ionisation energy
• Orbitals


  Clouds of negative charge where electrons are held
• Types of orbitals


  • s
  • p
  • d
  • f
• Orbitals


  • Each one can hold up to two electrons with opposite spins and has a different shape
• Blocks on the Periodic Table

  Correspond with different types of orbitals, each element in the block has outer electrons in that orbital