Group 1 and Group 2

• Which is more thermally stable?

  Group 1 compounds are more thermally stable than group 2 compounds
• Why is group 1 more thermally stable than group 2?

  because the greater the charge, the less distortion, so the less thermally stable the nitrate/carbonate compound becomes. Group 2 have a 2+ charge so they’re less stable.
• Explain why thermal stability increases down a group:

  • Carbonate and nitrate ions are large anions and can be made unstable by the presence of a cation.
  • This will polarize the anion making it distorted so therefore less stable.
  • Large cations cause less distortion due to the lower charge density.
  • Further down the group the cations are larger, so there is charge density is smaller so the carbonate/nitrate ion is more stable.
• How do group 2 carbonates decompose?

  MCO3 (s) —> MO (s) + CO2(g)
• How do group 2 nitrates decompose?

  2M(NO3)2 (s) —> 2MO (s) +4NO2 (g) + O2 (g)
• How do group 1 nitrates decompose?

  2MNO3 (s) —>2MNO2 (s) + O2 (s)
• How does lithium nitrate decompose ?

  LiNO3 —> Li2O +NO2+O2
• How do you test for how easily nitrates decompose?

  • You can measure the amount of oxygen produces (enough to light up growing splint
  • How long it takes to produce NO2. This must be carried out in a fume cupboard as NO2 is toxic
• how to measure how easily carbonates decompose

  you can measure how long it takes for CO2 to be produced. This can be tested for by using limewater. It will go cloudy in the presence of CO2
• What color is Li+ flame?

  scarlet red
• What color is Na+ flame ?

  yellow
• What color is K+ flame?

  Lilac
• What color is Rb+ flame ?

  Red
• What color is Cs+ flame ?

  Blue
• What color is Mg+ flame ?

  no color
• What color is Ca 2+ flame ?

  brick red
• What color is Sr2+ flame ?

  red
• What color is Ba 2+ flame?

  Apple green
• How do you carry out a flame test?

  • Mix a small amount of the compound your using with HCl
  • Heat a piece of platinum wire on a hot bunsen flame to clean it
  • Dip the wire in the acid mixture and hold it at the inner cone of the blue flame and observe the produced colour
• Why do flame tests produce a colour?

  • The energy absorbed during flame tests causes electrons to move to a higher energy level
  • As the the electrons fall back down to a lower energy level, energy is released in the form of electromagnetic waves which are sometimes in the form a visible light so it is observed
  • However sometimes it can be released in the form of infrared or ultraviolet