Group 1 and 2 thermal stability Flashcards
Thermal decomposition
When a substance breaks down (decomposes) when heated
Thermal stability affect on thermal decomposition
If a substance has HIGHER THERMAL STABILITY then it requires MORE ENERGY to decompose
What affects the stability of a compound?
The ionic radii of the metal cation
The positive charge of the metal cation
These affect the distortion of the compound
How does distortion occur within a metal compound?
The metal ion’s presence can polarise the anion and make it unstable = distortion
How does the size of cations affect distortion of anion?
Smaller cations have a larger charge density (more charge spread over a smaller area) than larger ones so polarises the anion more = causing more distortion
So thermal stability increases down a group
How does the charge of cations affect the distortion of the anion?
Greater charge (eg group 2 +2) means greater polarisation so less thermostable
Therefore group 2 requires less energy to decompose than 1
Do group 1 carbonates decompose with a Bunsen burner?
No because they are thermostable enough not to due to +1 charge of cation
Exception to decomposition of group 1 carbonates
Lithium because it is smallest (ionic radii) so has a higher charge density = greater polarisation = greater distortion = less thermostable
What does lithium carbonate decompose to?
Lithium oxide and carbon dioxide
Group 1 nitrates decompose to
Metal nitrite MNO2 (s)
Oxygen gas
Exception to group 1 nitrates decomposition
Lithium nitrate
What does lithium nitrate decompose to?
Lithium oxide, nitrogen dioxide and oxygen gas
Same as group 2 nitrates
What do group 2 carbonates decompose to?
Metal oxide and carbon dioxide
What do group 2 nitrates decompose to?
Metal oxide, nitrogen dioxide and oxygen
How can you find how easily carbonates decompose?
How long it takes for the carbonate to produce a certain amount of oxygen on heating (collect in gas syringe)
Or nitrogen dioxide
