©HOPTON. THE s-BLOCK ELEMENTS Elements in Group I (alkali metals) and Group II (alkaline earths)...

©HOPTON

THE s-BLOCK ELEMENTS

Elements in Group I (alkali metals) and Group II (alkaline earths) are known ass-block elements because their valence (bonding) electrons are in s orbitals.

Could you write down the electron configuration for the first 3 alkali metals and alkaline earth metals?

©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

Rn

Li

Na

K

Rb

Cs

Fr

Gp II

ALKALINE EARTHSALKALI 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

Rn

Li

Na

K

Rb

Cs

Fr

Gp II

ALKALINE EARTHSALKALI METALS

1s2 2s2

Francium and radium are both short-lived radioactive elementsFrancium 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 38Atomic 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



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



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 0.191Atomic radius / nm

Ba

0.198

2,2 2,8,2 2,8,8,2 2,8,18,8,2Electronic 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 0.191Atomic radius / nm

Ba

0.198


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 0.191Atomic radius / nm

Ba

0.198


• 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 protons1s2 2s2 2p6 3s2

11 protons1s2 2s2 2p6 3s1

©HOPTON

GROUP TRENDS


Be Mg Ca Sr

0.106 0.140 0.174 0.191Atomic radius / nm

Ba

0.198


Be2+ Mg2+ Ca2+ Sr2+

0.030 0.064 0.094 0.110Ionic radius / nm

Ba2+

0.134

2 2,8 2,8,8 2,8,18,8Electronic config. 2,8,18,18,8

©HOPTON

GROUP TRENDS


Be Mg Ca Sr

0.106 0.140 0.174 0.191Atomic radius / nm

Ba

0.198


Be2+ Mg2+ Ca2+ Sr2+

0.030 0.064 0.094 0.110Ionic radius / nm

Ba2+

0.134


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 0.191Atomic radius / nm

Ba

0.198


Be2+ Mg2+ Ca2+ Sr2+

0.030 0.064 0.094 0.110Ionic radius / nm

Ba2+

0.134




1s2 2s2 2p6 3s2 1s2 2s2 2p6

©HOPTON

GROUP TRENDS


Be Mg Ca Sr

0.106 0.140 0.174 0.191Atomic radius / nm

Ba

0.198


Be2+ Mg2+ Ca2+ Sr2+

0.030 0.064 0.094 0.110Ionic radius / nm

Ba2+

0.134




1s2 2s2 2p6 3s2 1s2 2s2 2p6 3s23p64s21s2 2s2 2p6 1s2 2s2 2p6 3s23p6

©HOPTON

GROUP TRENDS

MELTING POINT

Be Mg Ca Sr

2,2 2,8,2 2,8,8,2 2,8,18,8,2Electronic config.

1283 650 850 770Melting point / ºC

Ba

2,8,18,18,8,2

710

©HOPTON

GROUP TRENDS

DECREASES down Group

MELTING POINT

Be Mg Ca Sr



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



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



Ba

2,8,18,18,8,2

710



©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



Ba

2,8,18,18,8,2

710



©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 GroupDespite the increasing nuclear charge the values decrease due to theextra 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



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

BERYLLIUMThere are 4 protons pulling on the outer shell electrons

1st I.E. = 899 kJ mol-1

4+

©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


1st I.E. = 899 kJ mol-1

12+4+

MAGNESIUMThere 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

©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


1st I.E. = 899 kJ mol-1

12+4+

MAGNESIUMThere 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

©HOPTON

©HOPTON

SUCCESSIVE IONISATION ENERGIES

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

©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

12+

1st I.E. = 738 kJ mol-1

©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

12+

1st I.E. = 738 kJ mol-1

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.

©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

12+

1st I.E. = 738 kJ mol-1

12+ 12+

2nd I.E. = 1500 kJ mol-1




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


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




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

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 -22Mg(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 -22Mg(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



©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



Reactionwith water Be Mg Ca Sr

NONE reacts reacts reactsReactivity with water

Ba

reacts

Insoluble Sparinglysoluble

Slightlysoluble

Quitesoluble

Verysoluble

- 9-10

Solubility of hydroxide g/100cm3 of water

pH of solution

©HOPTON

OXIDES OF GROUP II



Reactionwith water

React with water to produce the hydroxide (not Be)

e.g. CaO(s) + H2O(l) —> Ca(OH)2(s)

Be Mg Ca Sr


Ba

reacts


Slightlysoluble

Quitesoluble

Verysoluble

- 9-10

Solubility of hydroxide g/100cm3 of water

pH of solution

©HOPTON

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




Be Mg Ca Sr


Ba

reacts


Slightlysoluble

Quitesoluble

Verysoluble

- 9-10

Solubility of hydroxide in water

pH of solution

©HOPTON




Be Mg Ca Sr


Ba

reacts


Slightlysoluble

Quitesoluble

Verysoluble

- 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.

©HOPTON


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

CARBONATES OF GROUP II

©HOPTON


Properties

• insoluble in waterMgCO3 CaCO3 SrCO3 BaCO3

1.5 x 10-4 1.3 x 10-5 7.4 x 10-6 9.1 x 10-6Solubility g/100cm3 of water

©HOPTON


Properties

• insoluble in water

• undergo thermal decomposition to oxide and carbon dioxide e.g. MgCO3(s) —> MgO(s) + CO2(g)

MgCO3 CaCO3 SrCO3 BaCO3

1.5 x 10-4 1.3 x 10-5 7.4 x 10-6 9.1 x 10-6

980

Solubility g/100cm3 of water

Decomposition temperature / ºC 400 1280 1360

©HOPTON


Properties



• the ease of decomposition decreases down the group


1.5 x 10-4 1.3 x 10-5 7.4 x 10-6 9.1 x 10-6

980



©HOPTON


Properties





1.5 x 10-4 1.3 x 10-5 7.4 x 10-6 9.1 x 10-6

980



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.

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

MgSO4 CaSO4 SrSO4 BaSO4


GROUP TRENDS

SULPHATES

©HOPTON



GROUP TRENDS

SULPHATES

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



GROUP TRENDS

SULPHATES



Greater charge density of Mg2+ ion means that it is more attracted to water

so the ionic lattice breaks up more easily

©HOPTON



GROUP TRENDS

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

©HOPTON



GROUP TRENDS

SULPHATES



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

©HOPTON

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©HOPTON. THE s-BLOCK ELEMENTS Elements in Group I (alkali metals) and Group II (alkaline earths)...

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