Periodicity

• How are the elements arranged in a periodic table?

  They are arranged in the order of increasing atomic numbers
• What is a period on a periodic table?

  The horizontal rows in the periodic table
• What is a group on a periodic table?

  The vertical columns
• What is meant by periodicity?

  The repeating trends in chemical and physical properties
• What change happens across each period?

  Elements change from metals to non metals
• How can the electron configuration be written in short?

  The noble gas before the element is used to abbreviate

  e.g. Li : 1s2 2s1

  Li : [He] 2s1
• Define first ionisation energy.

  The energy required to remove one electron from each atom in one mole of the gaseous element to form one mole of gaseous 1+ ions.
• Write an equation for the first ionisation energy of magnesium.

  Mg (g) -> Mg+ (g) + e-
• What are the factors that affect ionisation energy?

  • Atomic radius
  • Nuclear charge
  • Electron shielding or screening
• First ionisation energy increases across period 3 because of:

  • Increased nuclear charge
  • Decreased atomic radius
  • Same electron shielding

  which means more energy is needed to remove the first electron

  • Dips at Al because: outer electron is in a 3p orbital, higher energy than 3s orbital - less energy needed to remove electron
  • Dips at S because: one 3p orbital contains 2 electrons - repulsion between paired electrons - less energy needed to remove one