CONTENTS General properties Trends in electronic configuration Trends in atomic and ionic radius...

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

• Sulphates

GROUP IIGROUP II

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GROUP PROPERTIESGROUP PROPERTIES

GENERAL • metals

• all have the electronic configuration ... ns2

TRENDS • melting point

• electronic configuration

• electronegativity

• atomic size

• ionic size

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THE s-BLOCK ELEMENTSTHE 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.

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Gp I

Li

Na

K

Rb

Cs

Fr

ALKALI METALS

1s2 2s1

… 5s1

… 6s1

1s2 2s2 2p6 3s1

1s2 2s2 2p6 3s23p64s1

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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

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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

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Group 2: Alkaline-Earth Metals

Alkaline-earth metals are elements in Group 2. Alkaline-earth metal properties:

• group contains metals• 2 electrons in the outer level• very reactive, but less reactive than alkali metals• color of silver, higher densities than alkali metals

GROUP TRENDSGROUP 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 CONFIGURATIONELECTRONIC CONFIGURATION

4 12 20 38Atomic Number

Ba

… 6s2

2,8,18,18,8,2

56

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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

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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

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ATOMIC & IONIC RADIUSATOMIC & 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

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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

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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

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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

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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

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

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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

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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




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Variation of (I) atomic radius and (2) ionic radius down a group (II)


MELTING POINTMELTING 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

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DECREASES down Group


Be Mg Ca Sr



Ba

2,8,18,18,8,2

710

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• each atom contributes two electrons to the delocalised cloud

• metallic bonding gets weaker due to increased size of ion


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

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• Group I metals have lower melting points than the equivalent Group II metal because each metal only contributes one electron to the cloud


Be Mg Ca Sr



Ba

2,8,18,18,8,2

710



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• 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)


Be Mg Ca Sr



Ba

2,8,18,18,8,2

710



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Explaining the decrease in first ionisation energyIonisation energy is governed by•the charge on the nucleus,•the amount of screening by the inner electrons,•the distance between the outer electrons and the nucleus.

1st 2nd 3rd

Be 899.4 1757.1 14848

Mg 737.7 1450.7 7732.6

Ca 589.7 1145 4910

Sr 549.5 1064.2 4210

Ba 502.8 965.1 3600

FIRST IONISATION ENERGYFIRST IONISATION ENERGY

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

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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

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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+

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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

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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

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Variation of first ionization energydown a group (II)

G-IG-II

SUCCESSIVE IONISATION ENERGIESSUCCESSIVE 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

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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

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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.

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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.


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CHEMICAL PROPERTIES OF THE ELEMENTSCHEMICAL PROPERTIES OF THE ELEMENTS

Reactivity increases down the Group due to the ease of cation formation

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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)

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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-

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WATER react with increasing vigour down the group

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WATER react with increasing vigour down the group

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)

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• All Group II metals (except Be & Mg) react with H2O to form metal hydroxides and H2 gas

e.g.Ca(s) + 2H2O(l) Ca(OH)2(aq) + H2(g)

Sr(s) + 2H2O(l) Sr(OH)2(aq) + H2(g)• Be does not react with H2O(l or g)

Mg(s) + 2H2O(l) Mg(OH)2(s) + H2(g)

Mg(s) + H2O(g) MgO(s) + H2(g)

Magnesium reacts so slowly that only a small

bubble of hydrogen gas is produced even after

a few weeks. The other product is magnesium

hydroxide, which is only slightly soluble:

Ca reacts with H2O readily at room temperature

The hydroxides aren't very soluble, but they get more soluble as you go down the Group. The calcium hydroxide formed shows up mainly as a white precipitate (although some does dissolve). You get less precipitate as you go down the Group because more of the hydroxide dissolves in the water

Barium reacts very vigorously

with water

Strontium reacts vigorously with

cold water

Magnesium reacts with cold water exreamly slow

Clorine All group 2 elements react when heat in clorine

Ca + Cl2 —> CaCl2

* Berylium forms a covalent anhydrous cloride

* The other 2 metas form ionic chlorides

* The clorides have formula MgCl2


Reactions of the alkaline earth metals with chlorine. •All of the metals react similarly to give white, ionic chlorides.BeCl2 is essentially covalent, with comparatively low melting temperature.

•The lower members in group II form essentially ionic chlorides, with Mg having intermediate properties.•Describe what happens when Magnesium is heated and added to chlorine gas?•Write an equation for this •2Mg(s) + Cl2(g) MgCl2(s) •What is the general formula?•What is formed and what does it look like?•Is it soluble water? •Are the compounds formed ionic or covalent in character? How can you tell?•Account for the difference in reactivity between the two groups •Conclusion: Beryllium is more covalent as its melting point is less •This is due to it’s charge density

• Form normal oxides only, except Sr, Ba which can form peroxides

• All are basic (except BeO which is amphoteric)

• The reactivity of the group 2 metals towards water increases on descending the group.

• Group II oxides/hydroxides are generally less basic than Group I. Beryllium oxide/hydroxide are amphoteric.

2Be(s) + O2(g) 2BeO(s)

2Mg(s) + O2(g) 2MgO(s)

2Ca(s) + O2(g) 2CaO(s)

2Ba(s) + O2(g) 2BaO(s)

2BaO(s) + O2(g) 2BaO2(s)

Alkaline earth metals reacts with oxygen

The reaction of heated magnesium with steam is faster than the reaction of magnesium with cold water. This is mainly becauseA in cold water, the water molecules do not collide as frequently with magnesium.B the coating of oxide on magnesium decomposes when it is heated.C the fraction of particles with energy greater than the activation energy is higher in the reaction with steam.D the reaction with steam goes by an alternative route with lower activation energy.

Ans : C

Reactions of the oxides with water and acid• Experiment add MgO and CaO to water. Write

down your observations when the oxides are added to water

• What is happening, a reaction or simple dissolving?

• What do you observe when the oxides are added to acid you will measure the enthalpy change

• Write a conclusion

OXIDES OF GROUP IIOXIDES 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)

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• The reactivity increases down the group.

• The oxides of Ca, Sr, Ba react with

H2O(l) to give hydroxides

CaO(s) + H2O(l) Ca(OH)2(aq)

SrO(s) + H2O(l) Sr(OH)2(aq)

BaO(s) + H2O(l) Ba(OH)2(aq)

• MgO dissolves in acids to form salts but is

slightly soluble in water

• BeO is insoluble in both acids and water

Reactions of the oxides with water

Reactions of the oxides with acids All the oxides of alkaline earth metals reacts with dilute HNO3 and dilute HCl to form soluble nitrate and chloride.

CaO + 2HNO3 Ca(NO3)2 + H2O

BaO + 2HCl BaCl2 + H2O

Reaction of the oxides with H2SO4 is different from dilute HCl or HNO3.

MgO + H2SO4 MgSO4 + H2O

CaO + H2SO4 CaSO4(s) + H2O Suddenly reaction stopSrO + H2SO4 SrSO4(s) + H2OThis is due to insoluble CaSO4 & SrSO4 covers the oxide.( passive action)




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

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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

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HYDROXIDES OF GROUP IIHYDROXIDES OF GROUP II

Properties basic strength also increases down group

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• 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

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Be Mg Ca Sr


Ba

reacts


Slightlysoluble

Quitesoluble

Verysoluble

- 9-10

Solubility of hydroxide in water

pH of solution

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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

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Reactions of the hydroxides with acids All the alkali metal hydroxides react with dilute HCl & HNO3 as their oxides to produce soluble chloride and nitrate. Mg(OH)2(s) + 2HCl MgCl2 + 2H2O

Ca(OH)2(s) + 2HNO3 Mg(NO3)2 + 2H2O With H2SO4 reaction is like with the oxide.

Mg(OH)2(s) + H2SO4 MgSO4 + 2H2O

Ca(OH)2(s) + H2SO4 CaSO4(s) + 2H2O

Sr(OH)2(aq) + H2SO4 SrSO4(s) + 2H2O

Ba(OH)2(aq) + H2SO4 BaSO4(s) + 2H2O

reaction stops due to passive action

• No reaction between the oxides of s-block elements with

alkalis except BeO

• BeO is amphoteric, it reacts with NaOH to give

Na2Be(OH)4

BeO(s) + 2NaOH(aq) + H2O(l) Na2Be(OH)4(aq)

The trends in solubility of hydroxides

Compound Appearance In solid

Solubility of water

Mg(OH)2

Ca(OH)2

Sr(OH)2

Ba(OH)2

The trends in solubility of sulfates

Compound Appearance In solid

Solubility of water

MgSO4

CaSO4

SrSO4

BaSO4

MgSO4 CaSO4 SrSO4 BaSO4

3.6 x 10-1 1.1 x 10-3 6.2 x 10-5 9.0 x 10-7Solubility g/100cm3 of water


SULPHATESSULPHATES

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SULPHATESSULPHATES

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

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SULPHATESSULPHATES



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

so the ionic lattice breaks up more easily

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SULPHATESSULPHATES





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

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SULPHATESSULPHATES



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

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CARBONATES OF GROUP IICARBONATES 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

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

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

Thermal decomposition of metal carbonatesMetal carbonate

Decomposition temperature C

BeCO3 100

MgCO3 540

CaCO3 900

SrCO3 1280

BaCO3 1360

o

• Recall data:• What happens to carbonates when they are heated?• What is this reaction called?• What is the colourless gas called that is produced?• Conduct an experiment to see whether all the metals from

group 1 and 2 do the same thing• This equation is not balanced, see if you can do it.• Ag2CO3 Ag + CO2 + …………..

The shading is intended to show that there is a greater chance of finding them around the oxygen atoms than near the carbon.

Polarising the carbonate ionNow imagine what happens when this ion is placed next to a positive ion. The positive ion attracts the delocalised electrons inthe carbonate ion towards itself. The carbonate ion becomes polarised.

Effect of sizes of cations on thermal stability of compounds

+2

+2

+2

Metal carbonate

Decomposition temperature C

BeCO3 100

MgCO3 540

CaCO3 900

SrCO3 1280

BaCO3 1360

• Down the group, the size of cations increases

• polarizing power decreases

• compound with large anion become more stable

∴ thermal stability of carbonates & hydroxides of II metals increases down the group

o

The effect of heat on the Group 2 carbonatesAll the carbonates in this Group undergo thermal decomposition to give the metal oxide and carbon dioxide gas.

Thermal decomposition is the term given to splitting up a compound by heating it.

All of these carbonates are white solids, and the oxides that are produced are also white solids.

If "X" represents any one of the elements:

As you go down the Group, the carbonates have to be heated more strongly before they will decomposeXCO3(s) XO(s) + CO2(g) The carbonates become more stable to heat as you go down the group.

This end of the ion is on its way to breaking away and becoming carbon dioxide

The delocalised electrons are pulled towards the positive ion.

This oxygen atom is well on the way to becoming an oxide ion

Thermal decomposition of metal carbonates

Metal nitrates Decomposition temperature C

Be(NO3)2 60

Mg(NO3)2 89

Ca(NO3)2 561

Sr(NO3)2 570

Ba(NO3)2 700• Recall data:• What happens to nitrates when they are heated?• What is this reaction called?• What is the brown gas called that is produced?• Conduct an experiment to see whether all the metals

from group 1 and 2 do the same thing• This equation is not balanced, see if you can do it.• The nitrates also become more stable to heat as you go

down the Group. Cu(NO3)2 CuO + NO2 + O2

o

The nitrates also become more stable to heat as you go down the Group.Explaining the trend in terms of the polarising ability of the positive ion

A small 2+ ion has a lot of charge packed into a small volume of space. It has a high charge density and will have a marked distorting effect on any negative ions which happen to be near it.

A bigger 2+ ion has the same charge spread over a larger volume of space. Its charge density will be lower, and it willcause less distortion to nearby negative ions.

2X(NO3)2(s) 2XO(g) + 4NO2(g) + O2(g)

The effect of heat on the Group 2 nitratesAll the nitrates in this Group undergo thermal decomposition

to give the metal oxide, nitrogen dioxide and oxygen.The nitrates are white solids, and the oxides produced are also white solids. Brown nitrogen dioxide gas is given off

together with oxygen. Magnesium and calcium nitrates normally

have water of crystallisation, and the solid may dissolve in its own water of crystallisation to make a colourless solution

before it starts to decompose.Again, if "X" represents any one of the elements:

2X(NO3)(s) 2XO(s) + 4NO2(g) + O2(g)

As you go down the Group, the nitrates also have to be heated more strongly before they will decompose.

The nitrates also become more stable to heat as you go down the group

Measurement : Measure Time for the limewater to turn milky

Things to make the experiment fairConstant Bunsen lame/electrical heater settingFixed height of test tube above the flame Fixed volume/amount/mass of limewater

The carbonates of Group 2 in the Periodic Table decompose on heating to form the corresponding metal oxide and carbon dioxide. A general equation for the reaction isMCO3(s) MO(s) + CO2(g)The thermal stability of these carbonates can be compared in the laboratory using the apparatus in the diagram below. The test tube on the left contains a sample of a metal carbonate and the tube on the right contains lime water

(a) (i) State the measurement that you would make in this experiment.

(ii) Suggest three ways to make sure that, when carrying out this experiment, the thermal stabilities of the different

carbonates are compared fairly.(b) (i) State the trend in the thermal stability of the metal carbonates as the group is descended.*(ii) Explain this trend in stability.

Flame tests (use nichrome wire)• Clean the loop by dipping into acid and burn the

acid off in the flame.• Dip the loop into concentrated HCl acid.

• Dip the loop into metal salt • Put the loop in the flame and note the colour.

Characteristic Properties of the s-Block Elements

Group I element Flame colour Group II

element Flame colour

LiNaK

RbCs

Deep redGolden yellowLilac Bluish redBlue

CaSr

BaMg

Brick redBlood red orcrimsonGreenNo color

Why do we get different colours?

• Electrons are excited to a higher energy level by the heat

• When the electrons want to return to their original level they need to get rid of the energy gained

• Light is emitted of different wavelengths

1sn =1

n = 2

n = 3

n = 4

2s2p

3s

3p

4s

4s

3d

4p

4f

4d

e-

e-

Compounds containing lithium, sodium, potassium, calcium and barium can be recognised by burning the compound and observing the colours produced:

Lithium

Red

Sodium

Yellow

Potassium

Lilac

Calcium

Brick red

Barium

Green

Strontium

crimson

Moving down group 2 the following properties decreases

Be

Mg

Ca

Sr

Ba

Gp II

* Melting temperatures* Polarization power of cation* Ionisation energy

Moving down group 2 the following propertiesincreases

* Atomic and ionic radii* Thermal stability of the compounds* Reactivity of the metal

Gp I

Li

Na

K

Rb

Cs

H2O(l)Metal Hydroxide + H2

Cl2 (g) Colorless Ionic chlorides M+ Cl –

The clorides are soluable in water forming colorless solution

K + Cl2 (g) 2KCl(s)

Li + 2H2O (l) 2LiOH(aq) + H2 (g)

Be/BeO

Mg

CaCa

SrSr

BaBa

Gp II

H2O (l)

H2O(g)

H2O(l) Metal Oxide

Metal hydroxide

Salt + H2O

Dilute acids

H2O

Dilute acids

Metal Halides

Halogens

No reaction

Metal Oxide + H2

Metal Hydroxide +

H2

Summary of gr II metal reactions

O2

* All group 2 compounds reacts with O2 to produce Metal oxide*Mg reacts very slowly in cold water H2O(l) to form Mg(OH) 2 +H 2 *MgO reacts slightly with water

Except BeO

* Dilute acids example: HCl or HNO3

(white ionic chlorides)* Berylium forms a covalent anhydrous chloride with low melting point

(Basic Oxides) * BeO is amphoteric

Reactivity increases down the group

The hydroxides aren't very soluble, but they get more soluble as you go down the Group. The calcium hydroxide formed shows up mainly as a white precipitate (although some does dissolve). You get less precipitate as you go down the Group because more of the hydroxide dissolves in the water

Barium reacts very vigorously

with water

Strontium reacts vigorously with

cold water

Magnesium reacts with cold water exreamly slow

Reaction flow chart for Calcium metals

CaCaH2O CaO(s)

Ca(OH)2 (aq)

Ca(Cl)2 (aq) +H2O (l)

Dilute HCL

O2

Ca(Cl)2 (s)

Cl2(g)

Ca(OH)2 (aq) + H2 (g)

Dilute HCL

H2O

Observation : Bubbles of hydrogen gas are given off, and a white precipitate (of calcium hydroxide) is formed

Thermal stability of Group I and Group II Nitrates

Be

Gp I

Mg

Ca

Sr

Ba

Li

Na

K

Rb

Cs

Gp II

Metal Oxides +

NO2 + O2 Metal Nitrates + O2

Thermal decomposition of Group I and Group II Nitrates

2NaNO3 2NaNO2 + O2

2LiNO3 2Li2O + 4NO2 + O2

2Mg(NO3) 2 2MgO(s) + 4NO2 (g) + O2 (g)

Flow chart

Thermal stability increasesGoing down group 1 or 2 as :

• Atomic radius increases• Less polarization of Nitrate

ion

(Cations become larger down the group but Nitrate size is

not decreasing)

Thermal stability decreases as :• Atomic radius decrease• As charge increase• More polarization of Nitrate ion

Explain why potassium nitrate and calcium nitrate decompose to form differentProducts??

Calcium ions have greater positive charge(than potassium ions) or calcium ions are smaller (thanpotassium ions)

Calcium (ions) more polarising or cause greater distortion Of nitrate (ion) / anion

Thermal stability of Group I and Group II Carbonates

Thermal decomposition of Group I and Group II Carbonates

Li2CO3 Li2O + CO2

CaCO3 (s) CaO (s) + CO2

Flow chart

Be

Gp I

Mg

Ca

Sr

Ba

Li

Na

K

Rb

Cs

Gp II

Metal Oxides + CO2

No reaction Thermal stability increases

Going down group 1 or 2 as :• Atomic radius increases

• Less polarization of carbonate ion

(Cations become larger down the group but Carbonate size is

not decreasing)

Thermal stability decreases as :• Atomic radius decrease• As charge increase• More polarization of Nitrate ion

All group 1 compounds are soluble.

Solubility of Sulfates of group 2 decreases down the group

Hydroxides of group 2 increases down the group

CONTENTS General properties Trends in electronic configuration Trends in atomic and ionic radius...

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Transcript of CONTENTS General properties Trends in electronic configuration Trends in atomic and ionic radius...