4. Inorganic Chemistry (GROUP 2 & 1)

Question 1

What happens to the atomic radius as you go down group 2

Answer 1

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

Question 2

What happens to the melting point down group 2

Answer 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

Question 3

What happens to ionisation down group 2

Answer 3

decreases as distance from nucleus increases and shielding increases therefore weakening electrostatic attraction despite increased protons and nuclear charge

Question 4

What happens to the reactivity down group 2

Answer 4

The reactivity increases down the group as the atomic radii increase there is more shielding as the atom gets bigger. The nuclear attraction decreases and it is easier to remove (outer) electrons and so cations form more easily

Question 5

Group 2 + water

Answer 5

–> metal hydroxide + hydrogen

Question 6

Magnesium + H20 (g) steam

Answer 6

–> Magnesium oxide and hydrogen - magnesium burns with a bright white flame

Question 7

Group 2 + oxygen

Answer 7

–> metal oxide (solid white powder)

Question 8

Group 2 + chlorine

Answer 8

–> metal chloride

Question 9

What do hydroxides do to water

Answer 9

Oxides react readily with water to make hydroxides which disassociate to form OH- ions making the solution strongly alkaline

Question 10

Group 2 oxides + water

Answer 10

forms hydroxides which make the solution more alkaline
- MgO reacts very slowly (sparingly soluble ) and the hydroxide barely dissolves so not as basic
- Beryllium oxide doesn’t react with water at all and hydroxide is insoluble

Question 11

What happens to hydroxide solubility down the group 2

Answer 11

increases
- solutions become more alkaline as hydroxides become more soluble
(insoluble hydroxides form white precipitate)

Question 12

What are Group 2 hydroxides and and oxides ?

Answer 12

Bases

Question 13

Group 2 bases (hydroxide and oxide) + acid

Answer 13

Neutralisation reaction
forms –> salt +water

Question 14

What happens to solubility of sulfates down group 2

Answer 14

Decreases

Question 15

Explain why OH- solubility increases down group 2 and S042- solubility decreases down the group

Answer 15

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

Question 16

What is thermal decomposition

Answer 16

The use of heat to break down a reactant into more than one product

Question 17

Thermal decomposition of Group 2 carbonates

Answer 17

Break down into metal oxides and carbon dioxide
CaCO3(s) –> CaO(s) + CO2(g)

Question 18

Thermal decomposition of Group 2 nitrates

Answer 18

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

Question 19

Describe the thermal stability trend for carbonates and nitrates down group 2

Answer 19

thermal stability 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 and have a less polarising effect and distort 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

Question 20

Describe the thermal stability trend for carbonates of group 1 compared to group 2

Answer 20

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

Question 21

Explain why strontium requires less heat than barium to thermally decompose (Sr above Ba)

Answer 21

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+)

Question 22

Describe the trend for Group 1 nitrates decomposition

Answer 22

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