Lesson_1._Group_2 (1rgegergegegergge).ppt

Lesson 1.
GROUP II
Alkaline earths
1s2 2s2 2p6 3s2 1s2 2s2 2p6 3s23p64s2

Inquiry statement & Objectives
10.2.1.5 explain the patterns of changes in the physical and chemical
properties of elements of group 2 (II)
10.2.1.6 draw up a diagram of the carbonate cycle in nature and name their
areas of application

CONTENTS
• 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
• Sulfates
GROUP II
©HOPTON

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

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

Gp I
Li
Na
K
Rb
Cs
Fr
ALKALI METALS
1s2 2s1
… 5s1
… 6s1
1s2 2s2 2p6 3s1
1s2 2s2 2p6 3s23p64s1
©HOPTON

Be
Gp I
Mg
Ca
Sr
Ba
Ra
Li
Na
K
Rb
Cs
Fr
Gp II
ALKALINE EARTHS
ALKALI METALS
1s2 2s2
… 5s2
… 6s2
1s2 2s2 2p6 3s2
1s2 2s2 2p6 3s23p64s2
1s2 2s1
… 5s1
… 6s1
1s2 2s2 2p6 3s1
1s2 2s2 2p6 3s23p64s1
©HOPTON

Be
Gp I
Mg
Ca
Sr
Ba
Ra
Li
Na
K
Rb
Cs
Fr
Gp II
ALKALINE EARTHS
ALKALI METALS
1s2 2s2
Francium and radium are both
short-lived radioactive elements
… 5s2
… 6s2
1s2 2s2 2p6 3s2
1s2 2s2 2p6 3s23p64s2
1s2 2s1
… 5s1
… 6s1
1s2 2s2 2p6 3s1
1s2 2s2 2p6 3s23p64s1
©HOPTON

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

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

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

GROUP TRENDS
ATOMIC & IONIC RADIUS
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

GROUP TRENDS
ATOMIC RADIUS INCREASES down Group
• the greater the atomic number
the more electrons there are;
these go into shells increasingly
further from the nucleus
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
1s2 2s2 2p6 3s2 1s2 2s2 2p6 3s23p64s2
©HOPTON

GROUP TRENDS
ATOMIC RADIUS INCREASES down Group
• the greater the atomic number
the more electrons there are;
these go into shells increasingly
further from the nucleus
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
• atoms of Group II are smaller than
the equivalent Group I atom
the extra proton exerts a greater
attraction on the electrons
1s2 2s2 2p6 3s2 1s2 2s2 2p6 3s23p64s2
12 protons
1s2 2s2 2p6 3s2
11 protons
1s2 2s2 2p6 3s1
©HOPTON

GROUP TRENDS
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
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

GROUP TRENDS
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
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
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

GROUP TRENDS
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
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
1s2 2s2 2p6 3s2 1s2 2s2 2p6
©HOPTON

GROUP TRENDS
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
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
1s2 2s2 2p6 3s2 1s2 2s2 2p6 3s23p64s2
1s2 2s2 2p6 1s2 2s2 2p6 3s23p6
©HOPTON

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

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

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

GROUP TRENDS
• Group I metals have lower melting points than the equivalent Group II
metal because each metal only contributes one electron to the cloud
MELTING POINT
Be Mg Ca Sr
2,2 2,8,2 2,8,8,2 2,8,18,8,2
Electronic config.
1283 650 850 770
Melting point / ºC
Ba
2,8,18,18,8,2
710
Larger ions mean
that the electron
them as strongly
©HOPTON

GROUP TRENDS
• 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
MELTING POINT
Be Mg Ca Sr
2,2 2,8,2 2,8,8,2 2,8,18,8,2
Electronic config.
1283 650 850 770
Melting point / ºC
Ba
2,8,18,18,8,2
710
Larger ions mean
that the electron
them as strongly
©HOPTON

FIRST IONISATION ENERGY
©HOPTON

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

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

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

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

OXYGEN react with increasing vigour down the group
Mg burns readily with a bright white flame
0 0 +2 -2
2Mg(s) + O2(g) —> 2MgO(s)
Ba burns readily with an apple-green flame
2Ba(s) + O2(g) —> 2BaO(s)
©HOPTON

OXYGEN react with increasing vigour down the group
Mg burns readily with a bright white flame
0 0 +2 -2
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 —> Mg2+ + 2e¯
O + 2e¯ —> O2-
©HOPTON

WATER react with increasing vigour down the group
©HOPTON

Mg reacts very slowly with cold water
Mg(s) + 2H2O(l) —> Mg(OH)2(aq) + H2(g)
but reacts quickly with steam
Mg(s) + H2O(g) —> MgO(s) + H2(g)
©HOPTON

Mg reacts very slowly with cold water
Mg(s) + 2H2O(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) + 2H2O(l) —> Ba(OH)2(aq) + H2(g)
©HOPTON

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

OXIDES OF GROUP II
BaO (barium oxide)
Reaction
with water
©HOPTON
BeO MgO CaO SrO
NONE reacts reacts reacts
Reactivity with water
BaO
reacts
Insoluble Sparingly
soluble
Slightly
soluble
Quite
soluble
Very
soluble
- 9-10
Solubility of hydroxide
M(OH)2 in water
pH of 0.1M solution 12.5 13.1
13.0
10.4

OXIDES OF GROUP II
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)
©HOPTON
BeO MgO CaO SrO
NONE reacts reacts reacts
Reactivity with water
BaO
reacts
Insoluble Sparingly
soluble
Slightly
soluble
Quite
soluble
Very
soluble
- 9-10
Solubility of hydroxide
M(OH)2 in water
13.0
10.4

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

• 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

©HOPTON
Be(OH)2 Mg(OH)2 Ca(OH)2 Sr(OH)2 Ba(OH)2
Insoluble Sparingly
soluble
Slightly
soluble
Quite
soluble
Very
soluble
- 9-10
Solubility
in water
13.0
10.4

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.
©HOPTON
Be(OH)2 Mg(OH)2 Ca(OH)2 Sr(OH)2 Ba(OH)2
Insoluble Sparingly
soluble
Slightly
soluble
Quite
soluble
Very
soluble
- 9-10
Solubility
in water
13.0
10.4

Reactions of calcium oxide (“quick lime”) Calcium oxide reacts vigorously
with water to give calcium hydroxide (also known as slaked lime).
CaO + H 2 O →Ca(OH) 2
The resulting solution has a pH of 9 - 11
Uses
Ca(OH)2 used in agriculture to neutralise acid soils
Ca(OH)2(s) + 2H+ (aq) —> Ca2+(aq) + 2H2O(l)
Mg(OH)2 used in toothpaste and indigestion tablets as an antacid
Mg(OH)2(s) + 2H+ (aq) —> Mg2+(aq) + 2H2O(l)
Both the above are weak alkalis and not as caustic as sodium hydroxide
©HOPTON

Reaction of limewater with carbon dioxide.
©HOPTON
When carbon dioxide is passed through limewater it turns milky due to the
formation of insoluble calcium carbonate.
Ca(OH) 2 + CO 2 → CaCO 3 + H 2 O
This is the standard test for carbon dioxide.
https://www.youtube.com/watch?v=bkiJ3xzYnY8

Calcium carbonate
• Calcium carbonate decomposes when
heated… … forming calcium oxide.
• CaCO 3 → CaO + CO 2
• https://www.youtube.com/shorts/UPTShLCzcCg
• What can limestone be used for? Building
walls Building houses Limestone is also
used to make cement and concrete
• Neutralising excess acid in lakes or soils

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

Properties
• undergo thermal decomposition to oxide and carbon dioxide
e.g. MgCO3(s) —> MgO(s) + CO2(g)
1.5 x 10-4 1.3 x 10-5 7.4 x 10-6 9.1 x 10-6
980
Decomposition temperature / ºC 400 1280 1360
©HOPTON

Properties
1.5 x 10-4 1.3 x 10-5 7.4 x 10-6 9.1 x 10-6
980
One might think that the greater charge density of the smaller Mg2+ would mean that it
would hold onto the CO3
2- ion more and the ions would be more difficult to separate.
EASIER HARDER
©HOPTON

Properties
1.5 x 10-4 1.3 x 10-5 7.4 x 10-6 9.1 x 10-6
980
One might think that the greater charge density of the smaller Mg2+ would mean that it
would hold onto the CO3
2- 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.
EASIER HARDER
©HOPTON

3.6 x 10-1 1.1 x 10-3 6.2 x 10-5 9.0 x 10-7
GROUP TRENDS
SULFATES
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

3.6 x 10-1 1.1 x 10-3 6.2 x 10-5 9.0 x 10-7
GROUP TRENDS
SULFATES
Greater charge density of Mg2+ ion
means that it is more attracted to water
so the ionic lattice breaks up more easily
©HOPTON

3.6 x 10-1 1.1 x 10-3 6.2 x 10-5 9.0 x 10-7
GROUP TRENDS
SULFATES
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
©HOPTON

3.6 x 10-1 1.1 x 10-3 6.2 x 10-5 9.0 x 10-7
GROUP TRENDS
SULFATES
USE barium sulfate’s insolubility is used as a test for sulfates
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
©HOPTON

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