1. GROUP II Alkaline earths CONTENTS ©HOPTON General properties
Trends in electronic configuration
Trends in atomic and ionic radius
Trends in melting point
Trends in ionisation energy
Reaction with oxygen and water
Oxides and hydroxides
Carbonates
Sulphates
©HOPTON

2. GROUP PROPERTIES • all have the electronic configuration ... ns2
GENERAL • metals
• all have the electronic configuration ... ns2
TRENDS • melting point
• electronic configuration
• electronegativity
• atomic size
• ionic size
©HOPTON

3. THE s-BLOCK ELEMENTS
Elements in Group I (alkali metals) and Group II (alkaline earths) are known as
s-block elements because their valence (bonding) electrons are in s orbitals.
©HOPTON

4. THE s-BLOCK ELEMENTS Li Na K Rb Cs Fr
Elements in Group I (alkali metals) and Group II (alkaline earths) are known as
s-block elements because their valence (bonding) electrons are in s orbitals.
ALKALI METALS
Gp I Li
1s2 2s1 Na
1s2 2s2 2p6 3s1 K
1s2 2s2 2p6 3s23p64s1 Rb
… 5s1 Cs
… 6s1 Fr
©HOPTON

5. THE s-BLOCK ELEMENTS Li Be Na Mg K Ca Rb Sr Cs Ba Fr Rn
Elements in Group I (alkali metals) and Group II (alkaline earths) are known as
s-block elements because their valence (bonding) electrons are in s orbitals.
ALKALI METALS
ALKALINE EARTHS
Gp I
Gp II Li Be
1s2 2s1
1s2 2s2 Na Mg
1s2 2s2 2p6 3s1
1s2 2s2 2p6 3s2 K Ca
1s2 2s2 2p6 3s23p64s1
1s2 2s2 2p6 3s23p64s2 Rb Sr
… 5s1
… 5s2 Cs Ba
… 6s1
… 6s2 Fr Rn
©HOPTON

6. Francium and radium are both short-lived radioactive elements
THE s-BLOCK ELEMENTS
Elements in Group I (alkali metals) and Group II (alkaline earths) are known as
s-block elements because their valence (bonding) electrons are in s orbitals.
ALKALI METALS
ALKALINE EARTHS
Gp I
Gp II Li Be
1s2 2s1
1s2 2s2 Na Mg
1s2 2s2 2p6 3s1
1s2 2s2 2p6 3s2 K Ca
1s2 2s2 2p6 3s23p64s1
1s2 2s2 2p6 3s23p64s2 Rb Sr
… 5s1
… 5s2 Cs Ba
… 6s1
… 6s2 Fr Rn
Francium and radium are both short-lived radioactive elements
©HOPTON

7. ELECTRONIC CONFIGURATION
GROUP TRENDS
ELECTRONIC CONFIGURATION Be Mg Ca Sr Ba
Atomic Number 4 12 20 38 56
Old e/c
2,2
2,8,2
2,8,8,2
2,8,18,8,2
2,8,18,18,8,2
New e/c
1s2 2s2
…3s2
… 4s2
… 5s2
… 6s2
©HOPTON

8. ELECTRONIC CONFIGURATION
GROUP TRENDS
ELECTRONIC CONFIGURATION Be Mg Ca Sr Ba
Atomic Number 4 12 20 38 56
Old e/c
2,2
2,8,2
2,8,8,2
2,8,18,8,2
2,8,18,18,8,2
New e/c
1s2 2s2
…3s2
… 4s2
… 5s2
… 6s2
As the nuclear charge increases, the electrons go into shells further from the nucleus.
©HOPTON

9. ELECTRONIC CONFIGURATION
GROUP TRENDS
ELECTRONIC CONFIGURATION Be Mg Ca Sr Ba
Atomic Number 4 12 20 38 56
Old e/c
2,2
2,8,2
2,8,8,2
2,8,18,8,2
2,8,18,18,8,2
New e/c
1s2 2s2
…3s2
… 4s2
… 5s2
… 6s2
As the nuclear charge increases, the electrons go into shells further from the nucleus.
The extra distance of the outer shell from the nucleus affects…
Atomic radius Ionic radius
Ionisation energy Melting point
Chemical reactivity
©HOPTON

10. GROUP TRENDS ATOMIC & IONIC RADIUS ©HOPTON Be Mg Ca Sr 0.106 0.140
0.174
0.191
Atomic radius / nm Ba
0.198
2,2
2,8,2
2,8,8,2
2,8,18,8,2
Electronic config.
2,8,18,18,8,2
©HOPTON

11. GROUP TRENDS ATOMIC & IONIC RADIUS ATOMIC RADIUS INCREASES down GroupBe Mg Ca Sr
0.106
0.140
0.174
0.191
Atomic radius / nm Ba
0.198
2,2
2,8,2
2,8,8,2
2,8,18,8,2
Electronic config.
2,8,18,18,8,2
ATOMIC RADIUS INCREASES down Group
• the greater the atomic number
the more electrons there are;
these go into shells increasingly
further from the nucleus
1s2 2s2 2p6 3s2
1s2 2s2 2p6 3s23p64s2
©HOPTON

12. GROUP TRENDS ATOMIC & IONIC RADIUS ATOMIC RADIUS INCREASES down GroupBe Mg Ca Sr
0.106
0.140
0.174
0.191
Atomic radius / nm Ba
0.198
2,2
2,8,2
2,8,8,2
2,8,18,8,2
Electronic config.
2,8,18,18,8,2
ATOMIC RADIUS INCREASES down Group
• the greater the atomic number
the more electrons there are;
these go into shells increasingly
further from the nucleus
1s2 2s2 2p6 3s2
1s2 2s2 2p6 3s23p64s2
• atoms of Group II are smaller than
the equivalent Group I atom
the extra proton exerts a greater
attraction on the electrons
11 protons
1s2 2s2 2p6 3s1
12 protons
1s2 2s2 2p6 3s2
©HOPTON

13. GROUP TRENDS ATOMIC & IONIC RADIUS ©HOPTON Be Mg Ca Sr 0.106 0.140
0.174
0.191
Atomic radius / nm Ba
0.198
2,2
2,8,2
2,8,8,2
2,8,18,8,2
Electronic config.
2,8,18,18,8,2
Be2+
Mg2+
Ca2+
Sr2+
0.030
0.064
0.094
0.110
Ionic radius / nm
Ba2+
0.134 2
2,8
2,8,8
2,8,18,8
Electronic config.
2,8,18,18,8
©HOPTON

14. GROUP TRENDS ATOMIC & IONIC RADIUS IONIC RADIUS INCREASES down GroupBe Mg Ca Sr
0.106
0.140
0.174
0.191
Atomic radius / nm Ba
0.198
2,2
2,8,2
2,8,8,2
2,8,18,8,2
Electronic config.
2,8,18,18,8,2
Be2+
Mg2+
Ca2+
Sr2+
0.030
0.064
0.094
0.110
Ionic radius / nm
Ba2+
0.134 2
2,8
2,8,8
2,8,18,8
Electronic config.
2,8,18,18,8
IONIC RADIUS INCREASES down Group
• ions are smaller than atoms – on removing the outer shell
electrons, the remaining electrons are now in fewer shells
©HOPTON

15. GROUP TRENDS ATOMIC & IONIC RADIUS IONIC RADIUS INCREASES down GroupBe Mg Ca Sr
0.106
0.140
0.174
0.191
Atomic radius / nm Ba
0.198
2,2
2,8,2
2,8,8,2
2,8,18,8,2
Electronic config.
2,8,18,18,8,2
Be2+
Mg2+
Ca2+
Sr2+
0.030
0.064
0.094
0.110
Ionic radius / nm
Ba2+
0.134 2
2,8
2,8,8
2,8,18,8
Electronic config.
2,8,18,18,8
IONIC RADIUS INCREASES down Group
• ions are smaller than atoms – on removing the outer shell
electrons, the remaining electrons are now in fewer shells
1s2 2s2 2p6 3s2
1s2 2s2 2p6
©HOPTON

16. GROUP TRENDS ATOMIC & IONIC RADIUS IONIC RADIUS INCREASES down GroupBe Mg Ca Sr
0.106
0.140
0.174
0.191
Atomic radius / nm Ba
0.198
2,2
2,8,2
2,8,8,2
2,8,18,8,2
Electronic config.
2,8,18,18,8,2
Be2+
Mg2+
Ca2+
Sr2+
0.030
0.064
0.094
0.110
Ionic radius / nm
Ba2+
0.134 2
2,8
2,8,8
2,8,18,8
Electronic config.
2,8,18,18,8
IONIC RADIUS INCREASES down Group
• ions are smaller than atoms – on removing the outer shell
electrons, the remaining electrons are now in fewer shells
©HOPTON
1s2 2s2 2p6 3s2
1s2 2s2 2p6
1s2 2s2 2p6 3s23p64s2
1s2 2s2 2p6 3s23p6

17. GROUP TRENDS MELTING POINT ©HOPTON Be Mg Ca Sr Ba Melting point / ºC
1283
650
850
770
710
Electronic config.
2,2
2,8,2
2,8,8,2
2,8,18,8,2
2,8,18,18,8,2
©HOPTON

18. GROUP TRENDS MELTING POINT DECREASES down Group ©HOPTON Be Mg Ca Sr Ba
Melting point / ºC
1283
650
850
770
710
Electronic config.
2,2
2,8,2
2,8,8,2
2,8,18,8,2
2,8,18,18,8,2
DECREASES down Group
©HOPTON

19. Larger ions mean that the electron cloud doesn’t bind them as strongly
GROUP TRENDS
MELTING POINT Be Mg Ca Sr Ba
Melting point / ºC
1283
650
850
770
710
Electronic config.
2,2
2,8,2
2,8,8,2
2,8,18,8,2
2,8,18,18,8,2
DECREASES down Group
• each atom contributes two electrons to the delocalised cloud
• metallic bonding gets weaker due to increased size of ion
Larger ions mean that the electron cloud doesn’t bind them as strongly
©HOPTON

20. Larger ions mean that the electron cloud doesn’t bind them as strongly
GROUP TRENDS
MELTING POINT Be Mg Ca Sr Ba
Melting point / ºC
1283
650
850
770
710
Electronic config.
2,2
2,8,2
2,8,8,2
2,8,18,8,2
2,8,18,18,8,2
DECREASES down Group
• each atom contributes two electrons to the delocalised cloud
• metallic bonding gets weaker due to increased size of ion
• Group I metals have lower melting points than the equivalent Group II
metal because each metal only contributes one electron to the cloud
Larger ions mean that the electron cloud doesn’t bind them as strongly
©HOPTON

21. Larger ions mean that the electron cloud doesn’t bind them as strongly
GROUP TRENDS
©HOPTON
MELTING POINT Be Mg Ca Sr Ba
Melting point / ºC
1283
650
850
770
710
Electronic config.
2,2
2,8,2
2,8,8,2
2,8,18,8,2
2,8,18,18,8,2
DECREASES down Group
• each atom contributes two electrons to the delocalised cloud
• metallic bonding gets weaker due to increased size of ion
• Group I metals have lower melting points than the equivalent Group II
metal because each metal only contributes one electron to the cloud
NOTE Magnesium doesn’t fit the trend because crystalline
structure can also affect the melting point of a metal
Larger ions mean that the electron cloud doesn’t bind them as strongly

22. FIRST IONISATION ENERGY
©HOPTON

23. FIRST IONISATION ENERGYBe Mg Ca Sr Ba
1st I.E. / kJ mol-1
899
738
590
550
500
2nd I.E. / kJ mol-1
1800
1500
1100
1100
1000
3rd I.E. / kJ mol-1
14849
7733
4912
4120
3390
©HOPTON

24. FIRST IONISATION ENERGYBe Mg Ca Sr Ba
1st I.E. / kJ mol-1
899
738
590
550
500
2nd I.E. / kJ mol-1
1800
1500
1100
1100
1000
3rd I.E. / kJ mol-1
14849
7733
4912
4120
3390
DECREASES down the Group
Despite the increasing nuclear charge the values decrease due to the
extra shielding provided by additional filled inner energy levels
©HOPTON

25. FIRST IONISATION ENERGYBe Mg Ca Sr Ba
1st I.E. / kJ mol-1
899
738
590
550
500
2nd I.E. / kJ mol-1
1800
1500
1100
1100
1000
3rd I.E. / kJ mol-1
14849
7733
4912
4120
3390
DECREASES down the Group
Despite the increasing nuclear charge the values decrease due to the
extra shielding provided by additional filled inner energy levels 4+
BERYLLIUM
There are 4 protons pulling on the outer shell electrons
1st I.E. = 899 kJ mol-1
©HOPTON

26. FIRST IONISATION ENERGYBe Mg Ca Sr Ba
1st I.E. / kJ mol-1
899
738
590
550
500
2nd I.E. / kJ mol-1
1800
1500
1100
1100
1000
3rd I.E. / kJ mol-1
14849
7733
4912
4120
3390
DECREASES down the Group
Despite the increasing nuclear charge the values decrease due to the
extra shielding provided by additional filled inner energy levels
12+ 4+
MAGNESIUM
There are now 12 protons pulling on the outer shell electrons. However, the extra filled inner shell shields the nucleus from the outer shell electrons. The effective nuclear charge is less and the electrons are easier to remove.
1st I.E. = 738 kJ mol-1
BERYLLIUM
There are 4 protons pulling on the outer shell electrons
1st I.E. = 899 kJ mol-1
©HOPTON

27. FIRST IONISATION ENERGY
©HOPTON Be Mg Ca Sr Ba
1st I.E. / kJ mol-1
899
738
590
550
500
2nd I.E. / kJ mol-1
1800
1500
1100
1100
1000
3rd I.E. / kJ mol-1
14849
7733
4912
4120
3390
DECREASES down the Group
Despite the increasing nuclear charge the values decrease due to the
extra shielding provided by additional filled inner energy levels
12+ 4+
MAGNESIUM
There are now 12 protons pulling on the outer shell electrons. However, the extra filled inner shell shield the nucleus from the outer shell electrons. The effective nuclear charge is less and the electrons are easier to remove.
1st I.E. = 738 kJ mol-1
BERYLLIUM
There are 4 protons pulling on the outer shell electrons
1st I.E. = 899 kJ mol-1
©HOPTON

28. SUCCESSIVE IONISATION ENERGIESBe Mg Ca Sr Ba
1st I.E. / kJ mol-1
899
738
590
550
500
2nd I.E. / kJ mol-1
1800
1500
1100
1100
1000
3rd I.E. / kJ mol-1
14849
7733
4912
4120
3390
Successive Ionisation Energy values get larger
©HOPTON

29. SUCCESSIVE IONISATION ENERGIESBe Mg Ca Sr Ba
1st I.E. / kJ mol-1
899
738
590
550
500
2nd I.E. / kJ mol-1
1800
1500
1100
1100
1000
3rd I.E. / kJ mol-1
14849
7733
4912
4120
3390
Successive Ionisation Energy values get larger
12+
1st I.E. = 738 kJ mol-1
©HOPTON

30. SUCCESSIVE IONISATION ENERGIESBe Mg Ca Sr Ba
1st I.E. / kJ mol-1
899
738
590
550
500
2nd I.E. / kJ mol-1
1800
1500
1100
1100
1000
3rd I.E. / kJ mol-1
14849
7733
4912
4120
3390
Successive Ionisation Energy values get larger
12+
12+
1st I.E. = 738 kJ mol-1
2nd I.E. = 1500 kJ mol-1
There are now 12 protons and only 11 electrons. The increased ratio of protons to electrons means that it is harder to pull an electron out.
©HOPTON

31. SUCCESSIVE IONISATION ENERGIESBe Mg Ca Sr Ba
1st I.E. / kJ mol-1
899
738
590
550
500
2nd I.E. / kJ mol-1
1800
1500
1100
1100
1000
3rd I.E. / kJ mol-1
14849
7733
4912
4120
3390
Successive Ionisation Energy values get larger
12+
12+
12+
1st I.E. = 738 kJ mol-1
2nd I.E. = 1500 kJ mol-1
There are now 12 protons and only 11 electrons. The increased ratio of protons to electrons means that it is harder to pull an electron out.
3rd I.E. = 7733 kJ mol-1
There is a big jump in IE because the electron being removed is from a shell nearer the nucleus; there is less shielding.
©HOPTON

32. SUCCESSIVE IONISATION ENERGIESBe Mg Ca Sr Ba
1st I.E. / kJ mol-1
899
738
590
550
500
2nd I.E. / kJ mol-1
1800
1500
1100
1100
1000
3rd I.E. / kJ mol-1
14849
7733
4912
4120
3390
Successive Ionisation Energy values get larger
12+
12+
12+
1st I.E. = 738 kJ mol-1
2nd I.E. = 1500 kJ mol-1
There are now 12 protons and only 11 electrons. The increased ratio of protons to electrons means that it is harder to pull an electron out.
3rd I.E. = 7733 kJ mol-1
There is a big jump in IE because the electron being removed is from a shell nearer the nucleus; there is less shielding.
©HOPTON

33. CHEMICAL PROPERTIES OF THE ELEMENTS
Reactivity increases down the Group due to the ease of cation formation
©HOPTON

34. CHEMICAL PROPERTIES OF THE ELEMENTS
Reactivity increases down the Group due to the ease of cation formation
OXYGEN react with increasing vigour down the group
Mg burns readily with a bright white flame
2Mg(s) O2(g) —> 2MgO(s)
Ba burns readily with an apple-green flame
2Ba(s) O2(g) —> 2BaO(s)
©HOPTON

35. CHEMICAL PROPERTIES OF THE ELEMENTS
Reactivity increases down the Group due to the ease of cation formation
OXYGEN react with increasing vigour down the group
Mg burns readily with a bright white flame
2Mg(s) O2(g) —> 2MgO(s)
Ba burns readily with an apple-green flame
2Ba(s) O2(g) —> 2BaO(s)
In both cases…
the metal is oxidised Oxidation No. increases from 0 to +2
oxygen is reduced Oxidation No. decreases from 0 to -2
Mg —> Mg e¯
O e¯ —> O2-
©HOPTON

36. CHEMICAL PROPERTIES OF THE ELEMENTS
Reactivity increases down the Group due to the ease of cation formation
©HOPTON

37. CHEMICAL PROPERTIES OF THE ELEMENTS
Reactivity increases down the Group due to the ease of cation formation
WATER react with increasing vigour down the group
©HOPTON

38. CHEMICAL PROPERTIES OF THE ELEMENTS
Reactivity increases down the Group due to the ease of cation formation
WATER react with increasing vigour down the group
Mg reacts very slowly with cold water
Mg(s) H2O(l) —> Mg(OH)2(aq) H2(g)
but reacts quickly with steam
Mg(s) H2O(g) —> MgO(s) H2(g)
©HOPTON

39. CHEMICAL PROPERTIES OF THE ELEMENTS
Reactivity increases down the Group due to the ease of cation formation
WATER react with increasing vigour down the group
Mg reacts very slowly with cold water
Mg(s) H2O(l) —> Mg(OH)2(aq) H2(g)
but reacts quickly with steam
Mg(s) H2O(g) —> MgO(s) H2(g)
Ba reacts vigorously with cold water
Ba(s) H2O(l) —> Ba(OH)2(aq) H2(g)
©HOPTON

40. OXIDES OF GROUP II
Bonding • ionic solids; EXCEPT BeO which has covalent character
• BeO (beryllium oxide) MgO (magnesium oxide)
CaO (calcium oxide) SrO (strontium oxide)
BaO (barium oxide)
©HOPTON

41. Solubility of hydroxide g/100cm3 of water
OXIDES OF GROUP II
Bonding • ionic solids; EXCEPT BeO which has covalent character
• BeO (beryllium oxide) MgO (magnesium oxide)
CaO (calcium oxide) SrO (strontium oxide)
BaO (barium oxide)
Reaction
with water Be Mg Ca Sr
NONE
reacts
Reactivity with water Ba
Insoluble
Sparingly
soluble
Slightly
Quite
Very -
9-10
Solubility of hydroxide g/100cm3 of water
pH of solution
©HOPTON

42. Solubility of hydroxide g/100cm3 of water
OXIDES OF GROUP II
Bonding • ionic solids; EXCEPT BeO which has covalent character
• BeO (beryllium oxide) MgO (magnesium oxide)
CaO (calcium oxide) SrO (strontium oxide)
BaO (barium oxide)
Reaction
with water
React with water to produce the hydroxide (not Be)
e.g. CaO(s) H2O(l) —> Ca(OH)2(s) Be Mg Ca Sr
NONE
reacts
Reactivity with water Ba
Insoluble
Sparingly
soluble
Slightly
Quite
Very -
9-10
Solubility of hydroxide g/100cm3 of water
pH of solution
©HOPTON

43. HYDROXIDES OF GROUP II
Properties basic strength also increases down group
©HOPTON

44. HYDROXIDES OF GROUP II
Properties basic strength also increases down group
• this is because the solubility increases
• the metal ions get larger so charge density decreases
• get a lower attraction between the OH¯ ions and larger 2+ ions
• the ions will split away from each other more easily
• there will be a greater concentration of OH¯ ions in water
©HOPTON

45. Solubility of hydroxide in water
HYDROXIDES OF GROUP II
Properties basic strength also increases down group
• this is because the solubility increases
• the metal ions get larger so charge density decreases
• get a lower attraction between the OH¯ ions and larger 2+ ions
• the ions will split away from each other more easily
• there will be a greater concentration of OH¯ ions in water Be Mg Ca Sr
NONE
reacts
Reactivity with water Ba
Insoluble
Sparingly
soluble
Slightly
Quite
Very -
9-10
Solubility of hydroxide in water
pH of solution
©HOPTON

46. Solubility of hydroxide in water
HYDROXIDES OF GROUP II
©HOPTON
Properties basic strength also increases down group
• this is because the solubility increases
• the metal ions get larger so charge density decreases
• get a lower attraction between the OH¯ ions and larger 2+ ions
• the ions will split away from each other more easily
• there will be a greater concentration of OH¯ ions in water Be Mg Ca Sr
NONE
reacts
Reactivity with water Ba
Insoluble
Sparingly
soluble
Slightly
Quite
Very -
9-10
Solubility of hydroxide in water
pH of solution
Lower charge density of the larger Ca2+ ion means that it doesn’t hold onto the OH¯ ions as strongly. More OH¯ get released into the water. It is more soluble and the solution has a larger pH.

47. Both the above are weak alkalis and not as caustic as sodium hydroxide
HYDROXIDES OF GROUP II
Uses
Ca(OH)2 used in agriculture to neutralise acid soils
Ca(OH)2(s) H+ (aq) —> Ca2+(aq) H2O(l)
Mg(OH)2 used in toothpaste and indigestion tablets as an antacid
Mg(OH)2(s) H+ (aq) —> Mg2+(aq) H2O(l)
Both the above are weak alkalis and not as caustic as sodium hydroxide
©HOPTON

48. CARBONATES OF GROUP II
©HOPTON

49. Solubility g/100cm3 of water
CARBONATES OF GROUP II
Properties
• insoluble in water
MgCO3
CaCO3
SrCO3
BaCO3
Solubility g/100cm3 of water
1.5 x 10-4
1.3 x 10-5
7.4 x 10-6
9.1 x 10-6
©HOPTON

50. Solubility g/100cm3 of water Decomposition temperature / ºC
CARBONATES OF GROUP II
Properties
• insoluble in water
• undergo thermal decomposition to oxide and carbon dioxide
e.g. MgCO3(s) —> MgO(s) CO2(g)
MgCO3
CaCO3
SrCO3
BaCO3
Solubility g/100cm3 of water
1.5 x 10-4
1.3 x 10-5
7.4 x 10-6
9.1 x 10-6
Decomposition temperature / ºC
400
980
1280
1360
©HOPTON

51. Solubility g/100cm3 of water Decomposition temperature / ºC
CARBONATES OF GROUP II
Properties
• insoluble in water
• undergo thermal decomposition to oxide and carbon dioxide
e.g. MgCO3(s) —> MgO(s) CO2(g)
• the ease of decomposition decreases down the group
MgCO3
CaCO3
SrCO3
BaCO3
Solubility g/100cm3 of water
1.5 x 10-4
1.3 x 10-5
7.4 x 10-6
9.1 x 10-6
Decomposition temperature / ºC
400
980
1280
1360
©HOPTON

52. Solubility g/100cm3 of water Decomposition temperature / ºC
CARBONATES OF GROUP II
Properties
• insoluble in water
• undergo thermal decomposition to oxide and carbon dioxide
e.g. MgCO3(s) —> MgO(s) CO2(g)
• the ease of decomposition decreases down the group
MgCO3
CaCO3
SrCO3
BaCO3
Solubility g/100cm3 of water
1.5 x 10-4
1.3 x 10-5
7.4 x 10-6
9.1 x 10-6
Decomposition temperature / ºC
400
980
1280
1360
EASIER
HARDER
©HOPTON

53. Solubility g/100cm3 of water Decomposition temperature / ºC
CARBONATES OF GROUP II
Properties
• insoluble in water
• undergo thermal decomposition to oxide and carbon dioxide
e.g. MgCO3(s) —> MgO(s) CO2(g)
• the ease of decomposition decreases down the group
MgCO3
CaCO3
SrCO3
BaCO3
Solubility g/100cm3 of water
1.5 x 10-4
1.3 x 10-5
7.4 x 10-6
9.1 x 10-6
Decomposition temperature / ºC
400
980
1280
1360
EASIER
HARDER
One might think that the greater charge density of the smaller Mg2+ would mean that it would hold onto the CO32- ion more and the ions would be more difficult to separate.
©HOPTON

54. Solubility g/100cm3 of water Decomposition temperature / ºC
CARBONATES OF GROUP II
©HOPTON
Properties
• insoluble in water
• undergo thermal decomposition to oxide and carbon dioxide
e.g. MgCO3(s) —> MgO(s) CO2(g)
• the ease of decomposition decreases down the group
MgCO3
CaCO3
SrCO3
BaCO3
Solubility g/100cm3 of water
1.5 x 10-4
1.3 x 10-5
7.4 x 10-6
9.1 x 10-6
Decomposition temperature / ºC
400
980
1280
1360
EASIER
HARDER
One might think that the greater charge density of the smaller Mg2+ would mean that it would hold onto the CO32- ion more and the ions would be more difficult to separate.
The driving force must be the formation of the oxide. The smaller ion with its greater charge density holds onto the O2- ion to make a more stable compound.

55. Solubility g/100cm3 of water
GROUP TRENDS
SULPHATES
MgSO4
CaSO4
SrSO4
BaSO4
3.6 x 10-1
1.1 x 10-3
6.2 x 10-5
9.0 x 10-7
Solubility g/100cm3 of water
©HOPTON

56. Solubility g/100cm3 of water
GROUP TRENDS
SULPHATES
MgSO4
CaSO4
SrSO4
BaSO4
3.6 x 10-1
1.1 x 10-3
6.2 x 10-5
9.0 x 10-7
Solubility g/100cm3 of water
SOLUBILITY DECREASES down the Group
• as the cation gets larger it has a lower charge density
• it becomes less attracted to the polar water molecules
©HOPTON

57. Solubility g/100cm3 of water
GROUP TRENDS
SULPHATES
MgSO4
CaSO4
SrSO4
BaSO4
3.6 x 10-1
1.1 x 10-3
6.2 x 10-5
9.0 x 10-7
Solubility g/100cm3 of water
SOLUBILITY DECREASES down the Group
• as the cation gets larger it has a lower charge density
• it becomes less attracted to the polar water molecules
Greater charge density of Mg2+ ion means that it is more attracted to water so the ionic lattice breaks up more easily
©HOPTON

58. Solubility g/100cm3 of water
GROUP TRENDS
SULPHATES
MgSO4
CaSO4
SrSO4
BaSO4
3.6 x 10-1
1.1 x 10-3
6.2 x 10-5
9.0 x 10-7
Solubility g/100cm3 of water
SOLUBILITY DECREASES down the Group
• as the cation gets larger it has a lower charge density
• it becomes less attracted to the polar water molecules
Lower charge density of larger Ca2+ means that it is less attracted to water so the ionic lattice breaks up less easily – IT IS LESS SOLUBLE
Greater charge density of Mg2+ ion means that it is more attracted to water so the ionic lattice breaks up more easily
©HOPTON

59. Solubility g/100cm3 of water
GROUP TRENDS
SULPHATES
MgSO4
CaSO4
SrSO4
BaSO4
3.6 x 10-1
1.1 x 10-3
6.2 x 10-5
9.0 x 10-7
Solubility g/100cm3 of water
SOLUBILITY DECREASES down the Group
• as the cation gets larger it has a lower charge density
• it becomes less attracted to the polar water molecules
USE barium sulphate’s insolubility is used as a test for sulphates
Lower charge density of larger Ca2+ means that it is less attracted to water so the ionic lattice breaks up less easily – IT IS LESS SOLUBLE
Greater charge density of Mg2+ ion means that it is more attracted to water so the ionic lattice breaks up more easily
©HOPTON