1. Chemsheets AS006 (Electron arrangement)
08/09/2018
GROUP 2 – PHYSICAL
AND CHEMICAL PROPERTIES
AND
USES

2. GROUP II Learning Objectives
Learners will:
1) know and be able to explain the uses of Ca(OH)2
understand and be able to account for trends in melting point, atomic radius, 1st ionisation energy, electronegativity
know and be able to account for the trends in reactivity with water, the
relative solubility of the hydroxides and sulfates
4) know and be able to explain the uses of Mg(OH)2 and Ca(OH)2
know the use of BaCl2 solution to test for sulfates and the use of BaSO4 in
medicine

3. Fuse School (Group2)

4. ATOMIC RADIUS Be Mg Ca Sr Ba
more electron shells
so bigger atoms

5. ATOMIC RADIUS

6. Why do Radii decrease across a Period
Atomic size gradually decreases from left to right across a period of elements. This is because, within a period all electrons are added to the same shell. At the same time, protons are being added to the nucleus. BUT we are not adding distance. This means that the nucleus attracts the electrons more strongly, pulling the atom's shell closer to the nucleus. The valence electrons are held closer towards the nucleus of the atom.

7. 1st IONISATION ENERGY General trend down group
atoms get bigger and the valence electrons move away from the pull of the nucleus
more shielding
therefore weaker attraction from nucleus to electron in outer shell

8. DECREASES down the Group
1st IONISATION ENERGY 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

9. 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.

10. MELTING POINT 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ Calcium (Ca) Mpt 850ºC
Strontium (Sr)
Mpt 768ºC e- e- e- e- 2+ e- 2+ 2+ e- 2+ e- e- 2+ e- 2+ 2+ e- 2+ e- e- e- e- e- e- e- e- e- e- 2+ e- 2+ e- e- 2+ 2+ 2+ e- 2+ e- e- e- e- e- e- e- 2+ 2+ 2+ e- 2+ e- e- e- e- e- 2+ 2+ 2+ 2+ e- e- e- 2+ 2+ 2+ e- e- e- e- 2+ 2+ e- 2+
General trend down group
weaker metallic bonding as the ions get bigger the sea of electrons are no longer as able to hold the larger ions together
as metal ions are bigger
so lower melting points

11. Chemical Reactions Group 2 Reaction Precipitates
Sulphates = (s) insoluble going down, except Mg+2(aq)
BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq)
B) Hydroxides opposite sulphates, only (s) = Mg+2(s)
MgCl2(aq) + 2NaOH(aq) → Mg(OH)2(s) + 2NaCl(aq)

12.  MgSO4 Mg(OH)2   CaSO4 Ca(OH)2 SrSO4 Sr(OH)2 BaSO4 Ba(OH)2
more soluble
more soluble
Mg is the key you see
Magnesium sulfate is soluble, while magnesium hydroxide is (X) not.
Opposite trends
Sulphates = (s) insoluble going down, except Mg+2(aq)
Hydroxides opposite of sulphates, only (s) is Mg+2(s)

13. Testing for Sulfate ions
You can test to see if a solution contains sulfate ions SO42- using barium chloride solution. To do this:
a few drops of dilute HCl are added to the solution
add a few drops of BaCl2 solution
The presence of a white precipitate of
barium sulfate shows the presence of
sulfate ions in the solution.
BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq)

14. When an IONIC substance dissolves, the ions separate and mix in with the water:
NaCl(s) NaCl(aq)

15. Mix solutions of two ionic compounds:
Mg(NO3)2(aq) H2SO4(aq)

16. they may just mix!
No reaction

17. Predicting Double Replacement Reactions
You could have used your knowledge of solubility to predict whether the previous reaction and if the subsequent reactions are spontaneous.

18. Ba(NO3)2(aq) H2SO4(aq) Mix solutions of two ionic compounds:
Will there react and form a ppt?
Ba(NO3)2(aq) H2SO4(aq)

19. Ba2+(aq) + SO42-(aq)  BaSO4(s)
or a precipitate may form (if it gives a combination of ions that is insoluble)
Ba2+(aq) + SO42-(aq)  BaSO4(s)
© AS July-15

20. MgCl2(aq) NaOH(aq)

21. Mg2+(aq) + 2 OH–(aq)  Mg(OH)2 (s)

22. BaCl2(aq) NaOH(aq)

23. No reaction because Ba2+ with OH- and NaCl are soluble

24. Group 2 sulphates sulphates = (s)
MgSO4
Soluble
CaSO4
Slightly soluble
Ca2+(aq) + SO42-(aq) → CaSO4(s)
SrSO4
Insoluble
Sr2+(aq) + SO42-(aq) → SrSO4(s)
BaSO4
Ba2+(aq) + SO42-(aq) → BaSO4(s)

25. Group 2 hydroxides Mg(OH)2 Ca(OH)2 Sr(OH)2 Ba(OH)2
Hydroxides opposite of sulphates,
Mg(OH)2
Ca(OH)2
Sr(OH)2
Ba(OH)2

26. Mg2+(aq) + 2 OH-(aq) → Mg(OH)2(s) Ca2+(aq) + 2 OH-(aq) → Ca(OH)2(s)
Group 2 hydroxides
Mg(OH)2
Insoluble
Mg2+(aq) + 2 OH-(aq) → Mg(OH)2(s)
Ca(OH)2
Slightly soluble
Ca2+(aq) + 2 OH-(aq) → Ca(OH)2(s)
Sr(OH)2
Soluble
Ba(OH)2
Souble

27.  MgSO4 Mg(OH)2   CaSO4 Ca(OH)2 SrSO4 Sr(OH)2 BaSO4 Ba(OH)2
more soluble
more soluble
Remember
- Opposite trends - Ca(OH)2 & CaSO4 sparingly soluble - BaSO4 insoluble

28. Gr 2 Rxs
Reactions with Hydrogen(Hydrides): Ca(s) + H2(g)→CaH2(s) Reactions with Oxygen: (beryllium does not react with oxygen) Sr(s) + O2(g) →SrO2(s) Reactions with Nitrogen: 3Mg(s) + N2(g) →Mg3N2(s) Reactions with Halogens: Mg s) + Cl2(g) →MgCl2(s) Reacts with cold water Mg(s) + 2H2O(l) —> Mg(OH)2(aq) + H2(g) Ba reacts vigorously with cold water, we are going down the table Ba(s) + 2H2O(l) —> Ba(OH)2(aq) + H2(g)

29. CHEMICAL PROPERTIES OF THE ELEMENTS
Reactivity increases down the Group due to the ease of cation formation
WATER react with increasing vigor 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 (steam is hot)
Mg(s) H2O(g) —> MgO(s) H2(g)
Ba reacts vigorously with cold water
Ba(s) H2O(l) —> Ba(OH)2(aq) H2(g)
Next USES…………………………………..

30. Barium meal
BaSO4

31. Uses of Ca(OH) 2 Calcium hydroxide or slacked lime:
Used as limewater to test for CO2
Cement
pH adjustment,
digestion aid ………..as is Mg(OH) 2
See next slides for uses

32. Slaked lime Ca(OH)2

33. Limestone /
calcium carbonate
CaCO3

34. Milk of magnesia
Mg(OH)2