Group 2, the alkaline earth metals
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Describe and explain the general trend in atomic radius down the group 2 metals
Atomic radius increases down the group More shells of electrons (stronger nuclear charge but more shielding ‘cancels out’)
Describe and explain the general trend in melting points down the group 2 metals
Melting points decrease down the group Increased nuclear charge, but more shielding so weakened nuclear attraction between outer electrons and nucleus
Describe and explain the general trend in first ionisation energies down the group 2 metals
Decreases as you go down the group Increased nuclear charge but more shielding (larger atom), so overall weaker attraction between the positively charged nucleus and negative outer electrons Therefore easier to remove
How does the reactivity of group 2 metals change down the group?
Reactivity increases down the group
A student wants to test the reaction rate of Mg with an acid. What should they do to the Mg ribbon first, and why?
Clean it with emery paper Outer Mg will react with oxygen to form MgO This will also react, but at a different rate, and so give a different result
Mg reacts with steam to give what products?
MgO and H2 gas
Mg reacts with warm water to give what products?
Mg(OH)2 + H2 gas
Give 2 differences between the reaction of Mg with water vs Mg with steam
Water gives Mg(OH)2 and H2 gas, steam gives MgO and H2 gas Water reaction is far slower Water reactions doesn’t give a flame
What would someone observe with the reaction between a group 2 element and cold water?
Fizzing Metal dissolving Solution heating up The effects increase down the group With Ca, formation of white ppt
Ti cannot be extracted using carbon. Why is this?
TiC (titanium carbide) formed instead
Describe how you would extract titanium
TiO2 (s) converted to TiCl4 (l) at 900C TiCl4 purified by fractional distillation in an Ar atmosphere Ti extracted by Mg in an Ar atmosphere at 500C
Give a reaction to show the extraction of Ti by Mg
TiCl4 + 2Mg –> Ti + 2MgCl2
Give 2 reasons why Ti is expensive
Expensive cost of Mg Batch process - slower, requires more energy, energy lost when reactor cooled after stopping Use of Ar and need to remove moisture High temperatures required in both steps
Why is TiO2 converted to TiCl4?
It can purified by fractional distillation - TiCl4 molecular so (l) at room temp., TiO2 (s) as molecular
State the general trend in Group 2 hydroxide solubilities down the group
Generally become more soluble down the group
Is Mg(OH)2 soluble in water?
Technically classified as being insoluble in water
What is Mg(OH)2 used for?
Used in medicine to neutralise excess acid in the stomach, and to treat constipation
Why is Mg(OH)2 preferable for treating stomach acid than CaCO3?
CaCO3 would produce CO2
What is Ca(OH)2 used for?
Used in agriculture to neutralise acidic soils Aq soln. of it (lime water) can also be used to test for CO2 - mill go milky (CaCO3 produced)
Describe the solubility of Ca(OH)2
Reasonably soluble in water
Describe the solubility of Ba(OH)2
Easily dissolves in water
Describe the general trend in Group 2 sulphate solubilities down the group
Sulphates become less soluble down the group
Describe the solubility of BaSO4
Insoluble
Give a use of BaSO4
Used in medicine as a ‘barium meal’ given to patients needing intestinal X-rays Ba absorbs the X-rays - show up darker