8.1 - Group 2

Question 1

What is the trend in reactivity down Group 2 and why?

Answer 1

• To react, group 2 elements lose 2 electrons
• Faster the electrons lose electrons, the faster the reaction

Factors to consider

1. Increase nuclear charge (more protons)
2. Increase atomic radius (decreases attractive force to nucleus)
3. Increase shielding (more inner shells to screen outer electrons from nuclear attraction)

The second and third factors outweigh nuclear charge

As you move down the group, reactivity increases as ionisation energies decrease

Question 2

What observations can you see when calcium reacts with water?

Answer 2

• Calcium slowsl dissolves
• Effervescence seen
• Steam possible
• White precipitate

Question 3

What type of compounds are metal oxides?

Answer 3

Bases

Bases dissolve to form alkalis

Question 4

What occurs when metal oxides react with water?

Answer 4

MO_(s) + H2O_(l) → M(OH)_2(aq

• Metal hydroxide solution forms
• Not all oxides are equally soluble
• Mg(OH)₂ is less soluble than barium and strontium hydroxide

Question 5

What is the trend in solubility and alkalinity for group 2 metal hydroxides?

Answer 5

• As you move down Group 2 solubility increases
• As you move down Group 2 alkalinity increases
  
  • ​Because, the more soluble the group 2 metal hydroxide, more hydroxide ions are available per mole of metal hydroxide, so pH increases
  • So since, solubility increases down the group, more hydroxide ions will be available, so alkalinity increases down the group

Question 6

What are the uses of group 2 compounds?

Answer 6

Ca(OH)₂

• Used in agriculture to increase the pH of acidic soils

Ca(OH)_2(s) + 2H⁺ ⇒ Ca²⁺_(aq) + 2H₂O_(l)

Mg(OH)₂; CaCO₃

• Used as antacids to treat acid indigestion