Explaining all about the common trends and properties of the Group 2 elements in the Periodic Table... With set objective and outcome...

1. 5.3 & 5.4 Group 2
What is the outcome from syllabus?
Candidates should be able to:
(a) describe the reactions of the elements with oxygen and water
(b) describe the behaviour of the oxides with water
(c) describe the thermal decomposition of the nitrates and carbonates
(d) interpret, and make predictions from, the trends in physical and
chemical properties of the elements and their compounds
(e) explain the use of magnesium oxide as a refractory lining material
and calcium carbonate as a building material
(f) describe the use of lime in agriculture

2. 5.3 Group 2
Sr
Ba
Ra
Ca
Be
Mg
Alkaline metal:
ns2
12+
Mg

3. BERYLLIUM
MAGNESIUM
CALCIUM
STRONTIUM
BARIUM
RADIUM
5.3 Group 2

4. 5.3 Group 2
Element Color Element Color
Li Scarlet Be －
Na Yellow Mg －
K Lilac Ca Brick-red
Rb Red Sr Crimson
Cs Blue Ba Apple-green
The Flame Color:

5. 5.3 Group 2
I II III IV
Li Be B C Period 2
Na Mg Al Si Period 3
Increasing electronegativity
Increasing
electronegativity
The untypically large electronegativities of Period 2 elements
(caused by their small size) mean that they are in some ways
more typical of elements one group to the right than to elements
of their own group.
Diagonal relationships ( 角对 线规则 )
For example: Be(OH)2 + 2H+
→ Be2+
+ 2H2O
Be(OH)2 + 2OHˉ→ [Be(OH)4]2ˉ

6. 5.3 Group 2
Electron
arrangement
Metallic
radius/nm
First +
Second IE/
kJ mol-1
Tm/K Tb/K Density
/g cm-3
Mg
Magnisum
[Ne]3s2
0.160 2189 922 1380 1.74
Ca
Calcium
[Ar]4s2
0.197 1735 1112 1757 1.54
Sr
Strontium
[Kr]5s2
0.215 1614 1042 1657 2.60
Ba
Barium
[Xe]6s2
0.224 1468 998 1913 3.51
The physical properties of Group 2:

7. Magnesium oxide
2Mg (s) + O2 (g) 2MgO (s)
① burns very vigorously
② bright white flame
③ white solid produced
a. in the air b. in oxygen
5.3 Group 2

8. 5.3 Group 2
The reason that there are different types of oxides is related to the
sizes of the ions:
O2
ˉ
> O2
2ˉ
> O2ˉ
If the cation is too small, it is not easy for enough peroxide or
superoxide ions to cluster round it to form a stable crystal
lattice. For example, Lithium can only forms the ‘normal’ oxide.
..
¨¨
OO¨¨.. ..
oxygen ion
¨¨ ¨¨
O—OO—O¨¨.. ....
superoxide ionperoxide ion
¨¨ ¨¨
O—OO—O¨¨ ¨¨.... ....22
..22
....

9. 5.3 Group 2
The ‘normal’ oxide, MO(M2+
+ O2ˉ
), is formed when the metals
are heated in oxygen. Strontium and Barium also form
peroxides. As the M2+
ions are smaller than the M+
ions in
Group I, peroxides do not form until lower down the group
II than in Group I.
The closer the anions with cations, the
more stable the ionic compounds crystal.

10. 5.3 Group 2
Mg (s) + 2H2O (l) Mg(OH)2 (aq) + H2 (g)
♦ Reaction with water
Mg (s) + H2O (g)
steam
MgO (s) + H2 (g)
slowly
rapidly
Beryllium does not react directly with water all. The rest of the Group
II metals react with increasing rapidity on descending the group.

11. 5.3 Group 2
MgO (s) + H2O (l)
♦ Oxide reaction with water
Partially soluble
The rest of the Group II oxides react with increasing rapidity on
descending the group.
Mg(OH)2 (aq)
In the saturated solution, pH(Mg(OH)2) = 10

12. ♦ Reaction with acids
5.3 Group 2
Mg (s) + 2HCl (aq) MgCl2 (aq) + H2 (g)
Mg (s) + H2SO4(aq) MgSO4 (aq) + H2 (g)
The reaction is more vigorous as we go down the group.

13. 5.3 Group 2
Carbonates,
CO3
2ˉ
Mg
Ca
Sr
Ba
MgCO3 → MgO + CO2
Group IIGroup II
Same pattern but higher
temperatures needed for
decomposition
Nitrates,
NO3
ˉ
Mg
Ca
Sr
Ba
M(NO3)2 → MO +
2NO2 + 1/2O2
Thermal stability describes how easily or otherwise a compound will
decompose on heating. Increased thermal stability means a higher
temperature is needed to decompose the compound.
The charge density (Z/r) of
the cations (polarization)
will affect the decomposition
temperature.
The larger value of Z/r,
The easier breaking up of
distorted anions:
CO3
2-
→ CO2 + O2-
NO3
2-
→ NO2 + O2-
Same pattern but higher
temperatures needed for
decomposition

14. 5.3 Group 2
Which one of the following equations represents the
reaction that occurs when calcium nitrate is heated
strongly?
A. Ca(NO3)2 → Ca(NO2)2 + O2
B. 2Ca(NO3)2 → 2CaO + 4NO2 + O2
C. Ca(NO3)2 → CaO + N2O + 2O2
D. 3Ca(NO3)2 → Ca3N2 + 4NO2 + 5O2
E. Ca(NO3)2 → CaO2 + 2NO2
√

15. 5.3 Group 2
Which one of the following elements is likely to have
an electronegativity similar to that of aluminium?
A. Barium
B. Beryllium
C. Calcium
D. Magnesium
E. Strontium
√ diagonal relationship

16. 5.3 Group 2
Which one of the following statements is true?
A. All nitrates of Group II metals are decomposed by heat
to give the oxide NO2
B. Aqueous sodium nitrate in acidic to litmus.
C. Aqueous ammonium nitrate is alkaline to litmus.
D. The alkali metal nitrites are insoluble in water.
E. Metals dissolve in concentrated nitric acid to give
hydrogen.
√

17. 5.4 Compounds of Group II Elements
coins cosmetics
pipeShip

18. 5.4 Compounds of Group II Elements
Oxide Melting point/℃
MgO 2852
CaO 2614
SrO 2430
BaO 1918
Table 1: the melting points of the oxides of the Group II elements.
As M2+
cationic size increases down the Group, the ionic bonds
become weaker, hence, less energy is needed to break the
bonds and a low melting point is expected.
refractory
material

19. Magnesium oxide is used to line industrial furnaces
because it has a very high melting point. Which type of
bond needs to be broken for magnesium oxide to melt?
A. co-ordinate
B. covalent
C. ionic
D. metallic
5.4 Compounds of Group II Elements
√

20. 5.4 Compounds of Group II Elements
CaCO3(limestone)
CaO(lime)Ca(OH)2(slaked lime)
Δ
+ H2O
+ CO2

21. 5.4 Compounds of Group II Elements
Acid + Base → Salt + Water
Ca(OH)2 (s) + 2HNO3(aq) → Ca(NO3)2(aq) + 2H2O(l)
This is a base and is used in agriculture to treat acidic soil.

22. A farmer spreads lime on land which has already been
treated with a nitrogenous fertilizer. Which reactions will
occur over a period of time?
1. Ca(OH)2 + CO2 → CaCO3 + H2O
2. Ca(OH)2 + 2H+
(aq) → Ca2+
(aq) + 2H2O
3. Ca(OH)2 + 2NH4
+
(aq) → Ca2+
(aq) + 2NH3 + 2H2O
5.4 Compounds of Group II Elements
√
√
√

23. 5.4 Compounds of Group II Elements
When decomposing in water, organic refuse is oxidised to
form carboxylic acids. The water becomes acidic and
aquatic life is destroyed.
Which additives are suitable to remove this acid pollution?
1. calcium carbonate
2. calcium hydroxide
3. potassium nitrate
√
√

24. 5.4 Compounds of Group II Elements
Hard water: Ca2+
, Mg2+
, SO4
2-
, Cl-
Soft water: Ca2+
, Mg2+
, HCO3
2-
Ca2+
(aq) + SO4
2-
(aq) → CaSO4(s)
“temporary hardness”
“permanent hardness”
Ca2+
(aq)+ 2HCO3
ˉ
(aq) → CaCO3
(s) + CO2
(g) + H2O(l)
Mg2+
(aq)+ 2HCO3
ˉ
(aq) → MgCO3
(s) + CO2
(g) + H2
O(l)
Δ
Δ

25. 5.4 Compounds of Group II Elements
scum
Ca2+
(aq) + 2C17H35COOˉ(aq) → Ca(C17
H35
COO)2
(s)
Mg2+
(aq) + 2C17
H35
COOˉ(aq) → Mg(C17
H35
COO)2
(s)
calcium stearate
magnesium stearate
stearate
stearate

26. 5.4 Compounds of Group II Elements
A number of methods can be used for softening water:
♦ Boiling removes temporary hardness, but is expensive.
♦ Calcium hydroxide is cheap and can be added to precipitate out
temporary hardness as calcium carbonate.
Ca(HCO3)2(aq) + Ca(OH)2(s) → 2CaCO3(s) + 2H2O(l)
♦ Sodium carbonate may be added to precipitate out calcium or
magnesium ions.
Mg2+
(aq) + Na2CO3(aq) → MgCO3(s) + 2Na+
(aq)
♦ Use ion exchange resins: plastic beads which contain sodium ions.

27. River water in a chalky agricultural area may contain Ca2+
, Mg2+
,
CO3
2-
, HCO3
-
, Cl-
and NO3
-
ions. In a waterworks, such water is
treated by adding a calculated quantity of calcium hydroxide.
Which will be precipitated following the addition of calcium
hydroxide?
A. CaCl2
B. CaCO3
C. MgCO3
D. Mg(NO3)2
5.4 Compounds of Group II Elements
√

28. Table 2: Active Ingredients in Commercial Antacid Tablets
Chemical Name
Chemical
Formula
Chemical Reaction
Magnesium
Hydroxide
Mg(OH)2
Mg(OH)2
+ 2H+
→
Mg2+
+ 2H2
O
Calcium Carbonate CaCO3
CaCO3
+ 2H+
→
Ca2+
+ H2
O + CO2
(g)
Sodium Bicarbonate NaHCO3
NaHCO3
+ H+
→
Na+
+ H2
O + CO2
(g)
Aluminum
Hydroxide
Al(OH)3
Al(OH)3
+ 3H+
→
Al3+
+ 3H2
O
Dihydroxyaluminum
Sodium Carbonate
NaAl(OH)2
CO3
NaAl(OH)2
CO3
+ 4H+
→ Na+
+ Al3+
+ 3H2
O +
CO2
(g)
5.4 Compounds of Group II Elements

29. 5.4 Compounds of Group II Elements
The metals of Group II react readily with oxygen to from
compounds of general formula MO. When each of these
oxides is added to water, which forms the most alkaline
solution?
A. MgO
B. CaO
C. SrO
D. BaO
√

30. 5.4 Compounds of Group II Elements
The solubility of some Group II metal
compounds in mmol·dm-3
Mg2+
Ca2+
Sr2+
Ba2+
CO3
2-
SO4
2-
CrO4
2-
C2O4
2-
1.5 1830 8500 5.7
0.13 47 870 0.05
0.07 0.71 5.9 0.29
0.09 0.009 0.01 0.52
decreases
down the
group

31. NaCl(s)(g)Clˉ+(g)Na+ →
781 kJ•mol-1－=latt
∆ H
定义 : 由无限 的气 正 子远离 态 负离 , 在 准状 下形成标 态
1mol 子晶体 的离 时 焓变 , 叫 晶体 的该种 晶格能 Hlatt 。
The enthalpy change when 1 mole of an ionic compound is
formed from its gaseous ions under standard conditions
(298K ， 100 kPa)
5.4 Compounds of Group II Elements

32. 5.4 Compounds of Group II Elements
Hydration Enthalpy(∆Hhyd , 水合热 ): The amount of
energy relaeased when one mole of aqueous ions is
formed from its gaseous ions.
Na+
(aq)(g) + aqNa+ →
∆Hhyd = － 406 kJ·mol-1

33. 5.4 Compounds of Group II Elements
When an ionic solid is dissolved in water, two processes
are taking place. They are the breakdown of the ionic
solid, and subsequent stabilization of the ions by water
molecules (hydration).
Na+
(g) + Clˉ(g)
∆Hlatt =
－ 776 kJ·mol-1
∆Hhyd =
－ 772 kJ·mol-1
∆Hsolu = ∆Hhyd － Hlatt
NaCl (s) Na+
(aq) + Clˉ(aq)
∆Hsolu

34. 5.4 Compounds of Group II Elements
For MSO4, SO4
2-
is quite large compared with M2+
.Going
down the group II, the increase in size of the cations ∆Hlatt does
not cause a significant change in the but the ∆Hhyd become less
and less negative down the group. As a result, the dissolution
process becomes less and less exothermic and the solubility of
the sulphates(VI) of Group II metals decreases down the
group.
For M(OH)2, OH-
and M2+
are of the same order of magnitude,
Going down the group II, the increase in size of the cations
∆Hhyd does not cause a significant change in the but the ∆Hlatt
become less and less negative down the group. As a result, the
dissolution process becomes less and less exothermic and the
solubility of the hydroxides of Group II metals increases down
the group.