4.1.4 - Thermal stability of group 2 compounds. Flashcards
What is thermal stability?
How stable a compound is when heated
What does it mean if a compound is very thermally stable?
Doesn’t decompose at all when heated.
What is unique about group 2 nitrates and carbonates when they are heated?
They don’t melt - they decompose
Why do group 2 nitrates and carbonates decompose but group 1 don’t?
Charge on a group 2 cation is double
Size of the atomic radius of a group 2 cation is smaller than a group 1 cation in the same period.
Nitrate ions and carbonate ions are more complex than chloride ions.
What happens to nitrate ions when they don’t decompose?
They turn into nitrite ions
By releasing oxygen gas
What happens to carbonate ions when they decompose?
Can change to oxide ion
Releasing carbon dioxide
Why does lithium decompose nitrates?
Small ionic radius and so is charge dense.
Distorts the electron cloud
Affects nitrate ion
What is observed when a nitrate is decomposed and what is observed when a nitrate isn’t decomposed?
Decomposed - Brown fumes
Not decomposed - No brown fumes
What is the word equation for lesser decomposition of nitrates?
Metal nitrate = Metal nitrite + oxygen
What is the word equation for greater decomposition of nitrates?
Metal nitrate = metal oxide + nitrogen dioxide + oxide
When does the greater decomposition of nitrates occur?
Lithium and all group 2 metals
What metals decompose carbonate ions?
Lithium and all of group 2 metals
What happens to the stability of group 2 carbonates as you descend group 2 and why does this happen?
Stability increases as the size of the ion increases so less polarisation occurs.
What happens when a group 1 metal other than lithium is headed with carbonate?
No decomposition occurs
What is formed when calcium carbonate is decomposed?
calcium oxide and carbon dioxide
