Group 2

Question 1

What is Valency?

Answer 1

Number of electrons an atom has to gain, lose or share ti form a chemical bond.
For group 2, valency is 2 (lose 2 electrons, oxidised from 0–>+2 )

Question 2

What are the physical properties of group 2?

Answer 2

Called alkaline earth metals.
- high mp+bp: held by strong metallic bonds between +metal ion and delocalised electrons which require lots energy overcome.
- good conductors electricity: contain delocalised electrons which are free to move and carry a charge.

Question 3

What is the trend down group 2?

Answer 3

Number protons increases.
Atomic radius increases so electron shielding increases.
Outer electron further from nucleus so less nuclear attraction so less energy required.
Reactivity increases.

Question 4

How do group 2 metals react with oxygen?

Answer 4

Burn with bright flame: magnesium (white), calcium (brick red) , strontium (crimson), barium (apple green).
Become more reactive as go down as 2 outer electrons easier to remove.
Metal is being oxidised to form an oxide ( e.g. 2Mg (s) + O2(g) —> 2MgO (s) )
Form an ionic bond with oxygen.

Question 5

How do group 2 metals react with water?

Answer 5

• rapidly to form hydroxide and hydrogen gas. Hydroxides group 2 have general formula (m(OH)2)
• observe solid dissolves/disappears and fizzing.
• reactivity increases as go down.
  E.g. Ca (s) + 2H2O (l) —> Ca(OH)2 (aq) +H2 (g). (Redox reaction)

Question 6

How does group 2 react with acid?

Answer 6

React to make a salt and hydrogen.
Reactivity increases as go down.

Question 7

What are the oxides and hydroxides of group 2 ?

Answer 7

• Oxides and hydroxides are bases and most are soluble in water so are also alkali.
• oxides react with water form solution of metal hydroxide (e.g. MgO (s) + H2O (l) -> Mg(OH)2 (aq) )
• hydroxides are bases and soluble in water so form alkaline solutions with pH 10-12
• As go down, solubility hydroxides increase (so release more OH- ions) and become more strongly alkaline. ( most soluble Ba(OH)2)

Question 8

What are uses of group 2 compounds?

Answer 8

• calcium hydroxide: use by farmers/gardeners to neutralise acidic soils (Ca(OH)2 (aq) + 2HCl (aq) -> CaCl2 (aq) + 2H2O (l) )
• magnesium hydroxide and calcium carbonate : neutralise excess acid in stomach ( CaCO3 (s) + 2HCl (aq) -> CaCl2 (aq) +H2O (l) +CO2 (g) )