Group 2 metals show
a similar TREND in
reactivity with water
to Group 1 (though
LESS reactive).
1. What is this trend?
2. How might you
explain it?
Reactivity increases down the
Group 1 and Group 2 because
metals further down these
groups are more readily
oxidised by a
substance such as hydrogen
that
is itself reduced.
A metal is oxidised more
readily if it has a low first
ionisation energy and so
little energy is required to
remove the outer most
electron
Reactivity increases down the
Group 1 and Group 2 because
metals further down these
groups are more readily
oxidised by a substance such as
hydrogen that is itself reduced.
A metal is oxidised more
readily if it has a low first
ionisation energy and so little
energy is required to remove
the outer most electron.
Group 2 metal 2nd ionisation
energy also decreases down
the group
Ca  Ca1+ + e-
Ca1+  Ca2+ + e-
B4 Mid End
C
Can I describe the reactions of group 2 metal
oxides and hydroxides?
B
Can I analyze an unknown compound using
solubility rules?
A
Can I explain trends in solubility of group 2
metal compounds?
Group 2 metal properties
1. Reaction with
oxygen
8. Solubility in
water
2. Reaction with
chlorine
Metals
Sulphates
Oxides
Hydroxides
3. Reaction with
water
7. Solubility in
water
4. Reaction with
water
5. Reaction with
acid
6. Reaction with
acid
Properties down group 2
1
b.
recall the reaction of the elements in group 2 with oxygen, chlorine and water
Reactions with oxygen
Metals burn in oxygen to form a simple metal oxide.
CaO is called quick lime and is used in farming to
counteract soil acidity! It is made commercially by the
thermal decomposition of limestone!
Properties down group 2
2
b.
recall the reaction of the elements in group 2 with oxygen, chlorine and water
Reaction with Chlorine
Properties down group 2
3
b.
recall the reaction of the elements in group 2 with oxygen, chlorine and water
Reactions with Water
Beryllium has no reaction with water or steam even at red heat
– This is due to a thick oxide layer on the surface
Magnesium has a very slight reaction with cold water.
The reaction soon stops because magnesium hydroxide is almost insoluble in
water and forms a barrier preventing further reaction.
Magnesium will react with STEAM to form the metal oxide and hydrogen gas.
Calcium, strontium and barium all react with cold water with increasing vigour
to give the metal hydroxide and hydrogen.
Properties down group 2
4
c.
recall the reactions of the oxides of group 2 elements with water and dilute acid,
and their hydroxides with dilute acid
Properties down group 2
5
c.
recall the reactions of the oxides of group 2 elements with water and dilute acid,
and their hydroxides with dilute acid
Reaction of Oxides with Hydrochloric/Nitric Acid
Properties down group 2
6
c.
recall the reactions of the oxides of group 2 elements with water and dilute acid,
and their hydroxides with dilute acid
Reaction of Hydroxides with Hydrochloric/Nitric Acid
Properties down group 2
7
d.
recall the trends in solubility of the hydroxides and sulfates of group 2 elements
Solubility is determined by two factors:
Lattice dissociation enthalpy (energy needed to break up a crystal lattice)
Hydration enthalpy (energy released when ions are hydrated)
Ionic size has an effect on these factors.
• Solubility of Hydroxides
• There is a decrease in lattice
dissociation enthalpy down the
group.
• This outweighs the change in
enthalpy of hydration.
• As a result, there is an INCREASE
in SOLUBILITY down the group.
insoluble
slightly soluble
soluble
soluble
Properties down group 2
8
d.
recall the trends in solubility of the hydroxides and sulfates of group 2 elements
Solubility is determined by two factors:
Lattice dissociation enthalpy (energy needed to break up a crystal lattice)
Hydration enthalpy (energy released when ions are hydrated)
Ionic size has an effect on these factors.
Solubility of Sulphates
Magnesium and calcium sulphates
are soluble.
Anion >> Cation: so lattice enthalpy
does not vary much down group as
cation size changes.
soluble
soluble
However, hydration enthalpy
decreases down the group.
Therefore, solubility decreases
down the group.
insoluble
insoluble
1. Write a symbol equation for Mg reacting with O2
2. Write a symbol equation for Be reacting with Cl2
3. Write a symbol equation for Mg reacting with steam
4. Name the 3 oxides that react readily with water
5. Write the symbol equations for Calcium oxide reacting with
Phosphoric acid (H3PO4) and nitric acid (HNO3)
6. Write the symbol equation for strontium hydroxide reacting with
sulphuric acid (H2SO4)
7. Which group 2 metal hydroxides will form the most alkaline
solution? Justify your answer
8. A soil sample is suspected of containing sulphate. The chloride of
what metal will produce a precipitate?
END
Group 2 metal compounds can be used for quick visual
QUALITATIVE analysis where with the a substance can be identified but
NOT quantified. Titrations are required for QUANTITATIVE analysis that
takes longer to carry out.
The presence of high levels of sulphate in water, though non-toxic,
indicates that there are other toxic pollutants present (often metals).
ALL metal sulphates are soluble in water except Barium Sulphate which
forms a white precipitate. Therefore adding a soluble barium compound
to acidified water is a test for sulphate ions. Adding a strong acid (e.g.
HCl) prevents barium carbonate from forming and giving a false result.
Identify which of these 3 unknown samples contains aluminum
sulphate. Write an ionic equation with state symbols for the reaction
that takes place for the sample with sulphate and the sample with
carbonate.
Sample
Test with
hydrochloric acid (1)
Test of gas from
(1) with
limewater
Test of (1) with
barium chloride
A
fizzing
Goes cloudy
No precipitate
B
nothing
Nothing
White
precipitate
C
nothing
nothing
No reaction
What anion is
present?
Explain trends in solubility of group 2
metal compounds with reference to
solution enthalpy and lattice enthalpy
Enthalpies of solution (kJ/mol)
Explain trends in solubility of group 2
metal compounds with reference to
solution enthalpy and lattice enthalpy
Extension Q:
Evaluate whether enthalpy of solution
values help to explain the trend in
solubility for group 2 halides, hydroxides
and sulphates
EXTRA INFO SLIDES