Periodicity:

• Periodic table then:


  Mandeleeve arranged elements in order of atomic mass

  • Lines up elements with similar properties
  • If they didn't fit the properties, he would swap elements around and leave gaps
  • Predicted properties of missing elements
• Periodic table now:


  Elements are arranged are linked to their physical and chemical properties
• Definition:


  Periodicity: repeating trend in properties of the elements across a period
• Ionisation energy:


  The energy required to remove one electron from each atom in one mol of gaseous atoms
• Ionisation energy

  Trend down a group:

  • Atomic radius increases - attraction between nucleus and outer e- decreases as the distance between then increases
  • More inner shells- inner shell electrons repel outer electron shells more, reducing the attraction between the nucleus and outer electrons
  • nuclear charge remains the same

  Therefore the first ionisation energy decreases
• Ionisation energy:


  Trent across a group:

  • nuclear charge increases- The number of protons increase therefore there is a greater attraction between the nucleus and the the outer electrons
  • Same shields
  • Atomic radius decreases: distance between the outer electrons and nucleus is smaller

  Therefore the first ionisation energy is increases
• Ionisation energy across period 2:


  Trend:

  • Increases generally
  • Falls at Be-B
  • Falls at N-O

  Be and B:

  • 2p shell in boron has a higher energy than 2s in Be therefore 2p electron is easier to remove resulting in the fall

  N and O:

  • In O2 the electrons are paired in the 2p orbital which means they repel, making it easier to remove than N in which the electrons are unpaired in the 2p orbital