Atomic structure

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


  Number of protons in an atom
• How is the mass number calculated?


  Number of protons + number of neutrons
• Define relative atomic mass


  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?


  Different forms of the same element, containing the same number of protons but different number of neutrons
• How many orbitals and electrons do these shells contain: 1s, 2p, 3s, 3d, 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
• What is an orbital?


  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?


  Have opposite spin as repel each other as both are negatively charged
• Explain why chromium does not fit the trend for electronic configuration


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


  It only has one electron in its 4s orbital before filling 3d
• What is electron impact ionisation?


  The sample is vaporised and an electron gun is used to fire high energy electrons which knocks off 1 electron of each particle so they become positive ions
• What is electrospray ionisation?


  Sample dissolved in a volatile substance and injected through a fine hypodermic needle giving a fine mist, tip of needle has a high voltage, gains a proton
• When would you use electron impact ionisation?


  For organic or inorganic molecules with a low formula mass
• When would you use electrospray ionisation?


  For substances with a higher molecular mass including biological molecules e.g. proteins
• Describe how a time of flight mass spectrometer works


  Positive ions are accelerated by an electric field to a constant kinetic energy, with ions of smaller m/z having higher velocity and arriving at the detector first
• What is first ionisation energy?


  The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions