4. Inorganic Chemistry (GROUP 2 & 1) Flashcards
What happens to the atomic radius as you go down group 2
increases due to more electron shells
–> each element down group 2 has an extra shell compared to the one above it so electron is further from the nucleus
What happens to the melting point down group 2
decrease as metallic bonding weakens as atomic size increases as there is a greater distance between delocalised electrons and positive ions therefore less electrostatic attraction
What happens to ionisation down group 2
decreases as distance from nucleus increases and shielding increases therefore weakening electrostatic attraction despite increased protons and nuclear charge
What happens to the reactivity down group 2
The reactivity increases down the group
As the atomic radii increases, there is more shielding as the atom gets bigger.
The nuclear attraction decreases and it is easier to remove (outer) electrons and requires less energy
cations form more easily
Group 2 + water
–> give the observations of the reaction
–> metal hydroxide + hydrogen
Observations:
–> fizzing, (more vigorous down group)
–>the metal dissolving, (faster down group)
–>the solution heating up (more down group)
-> with magnesium calcium a solid white precipitate appears (less precipitate forms down group)
Magnesium + H20 (g) steam
–> Magnesium oxide and hydrogen - magnesium burns with a bright white flame
Group 2 + oxygen
–> metal oxide (solid white powder)
Group 2 + chlorine
–> metal chloride
What do hydroxides do to water
Oxides react readily with water to make hydroxides which disassociate to form OH- ions making the solution strongly alkaline
Group 2 oxides + water
forms hydroxides which make the solution more alkaline
- MgO reacts very slowly (sparingly soluble ) and the hydroxide barely dissolves
- Beryllium oxide doesn’t react with water at all and hydroxide is insoluble
What is an aqueous solution of calcium hydroxide called, what can it test for, and what does it produce in this reaction?
Called limewater
Used to test for CO2
Limewater turns cloudy –> this is because calcium carbonate is produced.
Ca(OH)2 (aq) + CO2 (g) –> CaCO3 (s) + H2O(l)
What happens to hydroxide solubility down the group 2
increases down the group
- solutions become more alkaline as hydroxides become more soluble
(insoluble hydroxides form white precipitate)
–> Barium (bottom of group) hydroxide would easily dissolve
in water. The hydroxide ions present
would make the solution strongly
alkaline
What are Group 2 hydroxides and and oxides ?
Bases
Group 2 bases (hydroxide and oxide) + acid
Neutralisation reaction
forms –> salt +water
What happens to solubility of sulfates down group 2
Decreases
Explain why OH- solubility increases down group 2 and S042- solubility decreases down the group
Compounds of group 2 that contain singly charged anion (OH- ) increase in solubility
Compounds of group 2 that contain doubly charged anion (SO42- ) decrease in solubility
What is thermal decomposition
The use of heat to break down a reactant into more than one product
Do group 2 carbonates AND nitrates become more or less thermally stable down the group?
They become more thermally stable and thermally decompose less easily so more energy required to heat up
Thermal decomposition of Group 2 carbonates
Break down into metal oxides and carbon dioxide
CaCO3(s) –> CaO(s) + CO2(g)
Thermal decomposition of Group 2 nitrates
forms metal oxides, oxygen and and nitrogen oxide
2Mg(NO3)2 → 2MgO + 4NO2 + O2
- observing a brown gas evolving and white nitrate solid melts into colourless solution and resolidifies
Describe the thermal stability trend for carbonates and nitrates down group 2
thermal stability for carbonates INCREASES down group 2 (becomes MORE stable)
–> as the 2+ cations get bigger the charge is spread out over a larger area causing a lower charge density. So cation has a less polarising effect and distorts the carbonate ion less - the C-O bond is weakened less and so harder to break
–> carbonate/ nitrate ion has a large electron cloud that is more distorted with smaller ions which causes less thermal stability
–> smaller ions are found at the top of group 2
Describe the thermal stability trend for carbonates of group 1 compared to group 2
More thermally stable
As you go down group 1, charge density of the ions decreases.
Only Lithium has enough polarising power to cause the weakening of the C-O bond in the carbonate, and hence decompose when heated.
Group 1 undergo lesser thermal decomposition so are more thermally stable.
–> still produces metal oxide and carbon dioxide
Explain why strontium carbonate requires less heat than barium carbonate to thermally decompose (Sr above Ba)
SrCO3 will need to be heated to a lower temperature than BaCO3
- This is because it has a smaller ionic radius,
- so it has greater polarising power, so not as much energy is needed to break the C-O bond in the carbonate ion (as it is weakened more by the Sr2+)
Describe the trend for Group 1 nitrates decomposition
don’t decompose in the same way as G2
- forms a nitrite salt (NO2-) and oxygen instead
2NaNO3 → 2NaNO2 + O2
- lithium however decomposes in the same way as G2
4 LiNO3 → 2Li2O + 4NO2 + O2
