Atomic Structure

• Which letter is used to represent the atomic number of an atom?

  Z
• What does the atomic number tell us about an element?

  It indicates the number of protons in an atom.
• What letter represents mass number?

  A
• How is the mass number calculated?

  Mass number = number of protons + number of neutrons.
• Define relative atomic mass.

  It is the average mass of all isotopes of an element compared to ¹/₁₂ the mass of an atom of Carbon 12 (C¹²).
• What are isotopes of an element?


  Isotopes are different forms of the same element, containing the same number of protons but different numbers of neutrons.
• How many orbitals and electrons do the following shells contain: 1s, 2p, 3s, 3d, and 4s?

  • 1s: 1 orbital, 2 electrons
  • 2p: 3 orbitals, 6 electrons
  • 3s: 1 orbital, 2 electrons
  • 3d: 5 orbitals, 10 electrons
  • 4s: 1 orbital, 2 electrons
• Does 3d or 4s have a higher energy?

  3d has a higher energy than 4s.
• What is an orbital?

  An orbital is a region around the nucleus that can hold up to two electrons.
• What would be the relationship between 2 electrons in the same orbital in terms of their spin?

  They have opposite spin as they repel each other due to both being negative.
• Explain why chromium does not fit the trend for electronic configuration.

  Chromium has one electron in its 4s orbital before filling 3d.
• Explain why copper does not fit the trend for electronic configuration.

  Copper has one electron in its 4s orbital before filling 3d.
• What are the two types of ionisation for a mass spectrometer and how do they differ?

  1. Electron impact:

  • Uses an electron gun to knock off one electron from each particle, forming 1+ molecular ions that can fragment.

  1. Electrospray:

  • Sample is dissolved in a volatile solvent and injected to form an aerosol, producing XH+ ions with +1 charge and mass of Mr + 1, which rarely fragment.
• When would you use the different types of ionisation in a mass spectrometer?

  Electron impact is used for organic or inorganic molecules with a low formula mass, while electrospray is used for substances with a higher molecular mass, including biological molecules like proteins.
• Describe how a time of flight mass spectrometer works.


  1. Acceleration: Positive ions are attracted towards a negatively charged plate.
  2. Ion Drift: Ions pass through a hole in the plate, forming a beam with constant kinetic energy, traveling along a tube to the detector. Time of flight is proportional to the square root of mass.
  3. Detection: Positive ions pick up electrons, current flows, and m/z value and time of flight are recorded.
• Define first ionisation energy.

  It is the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions.
• Energy Levels


  Discrete values of energy that an electron can have.
• Orbitals


  Regions around the nucleus where the electron is most likely to be found.
• Subshells


  Set of orbitals that have the same shape and energy.
• Shells


  Main categories of subshells, with s, p, d, and f being the main ones.
• 3d


  A subshell with a specific shape and energy, having a higher energy than the 4s subshell.
• 4s


  A subshell with a specific shape and energy, having a lower energy than the 3d subshell.