1.1 Atomic Structure

• What is the mass number?

  Number of protons and neutrons in the nucleus
• What is atomic number?

  Number of protons (and electrons) in the nucleus
• What is an isotope?

  elements with the same number of protons and electrons but different number of neutrons
• Why do isotopes have the same chemical properties?


  same electronic configuration
• What is the relative isotopic mass?

  The mass of an atom of an isotope compared with 1/12th of the mass of an atom of carbon-12
• What is the relative atomic mass?

  The average mass of an atom of an element compared to 1/12th of the mass of an atom of carbon 12.
• What is the relative molecular mass?

  The average mass of a molecule of an element or compound to 1/12th of the mass of an atom of carbon-12
• When do you use mass spectrometry?

  Provides structural information to identify an unknown compound or determine the relative abundance of each isotope of an element
• What is the first stage of TOF and what are the different ways?

  1. Ionisation

  -> electron impact ionisation: gas atoms bombarded with high energy electrons. This knocks one electron off forming a 1+ ion

  -> electrospray ionisation: sample dissolved in a solvent, passed through a needle connected to a high voltage. Gains a H+ from solvent
• What is the second stage of TOF?

  2. Acceleration

  Ions are accelerated towards a negatively charged plate to give all ions constant kinetic energy. So the velocity of each ion depends on its mass. The bigger the ion the slower it travels
• What is the third stage of TOF?

  3. Ion Drift

  Ions pass through a hole in the negative plate forming a beam
• What is the final stage of TOF?

  4. Detection

  The positive ion picks up an electron which causes a current to flow. Flight times are recorded
• What does the current show?

  Gives information about the relative abundance of isotopes. The bigger the current the bigger the abundance
• How can you determine relative atomic mass from mass spec?

  Ar = Σ (relative isotopic mass x abundance) /100
• How many electrons can a shell hold?

  2
• What are electron shells made up of?

  Atomic orbitals which are regions in space where electrons may be foun
• What are the four main orbitals and how many shells do they contain?

  S - 1 orbital

  P - 3 orbitals

  D - 5 orbitals

  F - 7 orbitals
• What intrinsic property do electrons have?

  Have a spin. Electrons in the same orbital must spin in opposite direction to minimise repulsion
• What is the difference in energy levels between 3d and 4s and therefore the exception to the rule?

  4s is lower in energy than 3d therefore it fills first and loses electrons from this level first
• What is first ionisation energy?


  The energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions

  X(g) -> X+(g) + e-
• What do successive ionisation energies provide evidence for?

  Shell structure of atoms

  -> within each shell successive ionisation energies increase as there is less electron repulsion

  -> between shells, there are big jumps in ionisation energies as the electron is removed from a shell closer to the nucleus
• What factors affect ionisation energy?

  - atomic radii: the larger the atomic radius, the further away the outer electrons are held from the nucleus, and the smaller the nuclear attraction

  - nuclear charge: the greater the nuclear charge, the greater the attractive force on the outer electrons

  - shielding: electrons repel each other due to their negative charge. The greater the number of inner shells of electrons, the greater the repulsion of the outer shell of electrons
• How does ionisation energy change down a group?

  Decreases as the number of shells increases and therefore atomic radius and shielding so there is less of an attraction between +ve nucleus and outer electron
• How does ionisation energy change across a period?

  Increases as electrons are all added to the same shell resulting in a greater attraction