AN INTRODUCTION TO GROUP II Alkaline earths KNOCKHARDY PUBLISHING 2015 SPECIFICATIONS 1s 2 2s 2 2p 6 3s 2 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2

INTRODUCTION This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards. Individual students may use the material at home for revision purposes or it may be used for classroom teaching with an interactive white board. Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at... Navigation is achieved by... either clicking on the grey arrows at the foot of each page orusing the left and right arrow keys on the keyboard KNOCKHARDY PUBLISHING GROUP II (Alkaline Earths) ©HOPTON

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... ns 2 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

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. Gp I Li Na K Rb Cs Fr ALKALI METALS 1s 2 2s 1 … 5s 1 … 6s 1 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 ©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. Be Gp I Mg Ca Sr Ba Rn Li Na K Rb Cs Fr Gp II ALKALINE EARTHSALKALI METALS 1s 2 2s 2 … 5s 2 … 6s 2 1s 2 2s 2 2p 6 3s 2 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 1s 2 2s 1 … 5s 1 … 6s 1 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 ©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. Be Gp I Mg Ca Sr Ba Rn Li Na K Rb Cs Fr Gp II ALKALINE EARTHSALKALI METALS 1s 2 2s 2 Francium and radium are both short-lived radioactive elements … 5s 2 … 6s 2 1s 2 2s 2 2p 6 3s 2 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 1s 2 2s 1 … 5s 1 … 6s 1 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 ©HOPTON

GROUP TRENDS Be 1s 2 2s 2 Mg …3s 2 Ca … 4s 2 Sr … 5s 2 2,22,8,22,8,8,22,8,18,8,2 New e/c Old e/c ELECTRONIC CONFIGURATION Atomic Number Ba … 6s 2 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 1s 2 2s 2 Mg …3s 2 Ca … 4s 2 Sr … 5s 2 2,22,8,22,8,8,22,8,18,8,2 New e/c Old e/c ELECTRONIC CONFIGURATION Atomic Number Ba … 6s 2 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 radiusIonic radius Ionisation energyMelting point Chemical reactivity Be 1s 2 2s 2 Mg …3s 2 Ca … 4s 2 Sr … 5s 2 2,22,8,22,8,8,22,8,18,8,2 New e/c Old e/c ELECTRONIC CONFIGURATION Atomic Number Ba … 6s 2 2,8,18,18,8,2 56 ©HOPTON

GROUP TRENDS ATOMIC & IONIC RADIUS BeMgCaSr Atomic radius / nm Ba ,22,8,22,8,8,22,8,18,8,2Electronic config.2,8,18,18,8,2 ©HOPTON

GROUP TRENDS ATOMIC RADIUSINCREASES down Group the greater the atomic number the more electrons there are; these go into shells increasingly further from the nucleus ATOMIC & IONIC RADIUS BeMgCaSr Atomic radius / nm Ba ,22,8,22,8,8,22,8,18,8,2Electronic config.2,8,18,18,8,2 1s 2 2s 2 2p 6 3s 2 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 ©HOPTON

GROUP TRENDS ATOMIC RADIUSINCREASES down Group the greater the atomic number the more electrons there are; these go into shells increasingly further from the nucleus ATOMIC & IONIC RADIUS BeMgCaSr Atomic radius / nm Ba ,22,8,22,8,8,22,8,18,8,2Electronic config.2,8,18,18,8,2 atoms of Group II are smaller than the equivalent Group I atom the extra proton exerts a greater attraction on the electrons 1s 2 2s 2 2p 6 3s 2 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 12 protons 1s 2 2s 2 2p 6 3s 2 11 protons 1s 2 2s 2 2p 6 3s 1 ©HOPTON

GROUP TRENDS ATOMIC & IONIC RADIUS BeMgCaSr Atomic radius / nm Ba ,22,8,22,8,8,22,8,18,8,2Electronic config.2,8,18,18,8,2 Be 2+ Mg 2+ Ca 2+ Sr Ionic radius / nm Ba ,82,8,82,8,18,8Electronic config.2,8,18,18,8 ©HOPTON

GROUP TRENDS ATOMIC & IONIC RADIUS BeMgCaSr Atomic radius / nm Ba ,22,8,22,8,8,22,8,18,8,2Electronic config.2,8,18,18,8,2 Be 2+ Mg 2+ Ca 2+ Sr Ionic radius / nm Ba ,82,8,82,8,18,8Electronic config.2,8,18,18,8 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 ATOMIC & IONIC RADIUS BeMgCaSr Atomic radius / nm Ba ,22,8,22,8,8,22,8,18,8,2Electronic config.2,8,18,18,8,2 Be 2+ Mg 2+ Ca 2+ Sr Ionic radius / nm Ba ,82,8,82,8,18,8Electronic config.2,8,18,18,8 IONIC RADIUS INCREASES down Group ions are smaller than atoms – on removing the outer shell electrons, the remaining electrons are now in fewer shells 1s 2 2s 2 2p 6 3s 2 1s 2 2s 2 2p 6 ©HOPTON

GROUP TRENDS ATOMIC & IONIC RADIUS BeMgCaSr Atomic radius / nm Ba ,22,8,22,8,8,22,8,18,8,2Electronic config.2,8,18,18,8,2 Be 2+ Mg 2+ Ca 2+ Sr Ionic radius / nm Ba ,82,8,82,8,18,8Electronic config.2,8,18,18,8 IONIC RADIUS INCREASES down Group ions are smaller than atoms – on removing the outer shell electrons, the remaining electrons are now in fewer shells 1s 2 2s 2 2p 6 3s 2 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 1s 2 2s 2 2p 6 1s 2 2s 2 2p 6 3s 2 3p 6 ©HOPTON

GROUP TRENDS MELTING POINT BeMgCaSr 2,22,8,22,8,8,22,8,18,8,2Electronic config Melting point / ºC Ba 2,8,18,18,8,2 710 ©HOPTON

GROUP TRENDS DECREASES down Group MELTING POINT BeMgCaSr 2,22,8,22,8,8,22,8,18,8,2Electronic config Melting point / ºC Ba 2,8,18,18,8,2 710 ©HOPTON

GROUP TRENDS DECREASES down Group each atom contributes two electrons to the delocalised cloud metallic bonding gets weaker due to increased size of ion MELTING POINT BeMgCaSr 2,22,8,22,8,8,22,8,18,8,2Electronic config 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 DECREASES down Group each atom contributes two electrons to the delocalised cloud metallic bonding gets weaker due to increased size of ion 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 BeMgCaSr 2,22,8,22,8,8,22,8,18,8,2Electronic config 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 DECREASES down Group each atom contributes two electrons to the delocalised cloud metallic bonding gets weaker due to increased size of ion 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 BeMgCaSr 2,22,8,22,8,8,22,8,18,8,2Electronic config 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

FIRST IONISATION ENERGY ©HOPTON

FIRST IONISATION ENERGY BeMgCaSr st I.E. / kJ mol -1 Ba nd I.E. / kJ mol -1 3rd I.E. / kJ mol -1 ©HOPTON

FIRST IONISATION ENERGY DECREASES down the Group Despite the increasing nuclear charge the values decrease due to the extra shielding provided by additional filled inner energy levels BeMgCaSr st I.E. / kJ mol -1 Ba nd I.E. / kJ mol -1 3rd I.E. / kJ mol -1 ©HOPTON

FIRST IONISATION ENERGY DECREASES down the Group Despite the increasing nuclear charge the values decrease due to the extra shielding provided by additional filled inner energy levels BeMgCaSr st I.E. / kJ mol -1 Ba nd I.E. / kJ mol -1 3rd I.E. / kJ mol -1 BERYLLIUM There are 4 protons pulling on the outer shell electrons 1st I.E. = 899 kJ mol ©HOPTON

FIRST IONISATION ENERGY DECREASES down the Group Despite the increasing nuclear charge the values decrease due to the extra shielding provided by additional filled inner energy levels BeMgCaSr st I.E. / kJ mol -1 Ba nd I.E. / kJ mol -1 3rd I.E. / kJ mol -1 BERYLLIUM There are 4 protons pulling on the outer shell electrons 1st I.E. = 899 kJ mol MAGNESIUM There 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

FIRST IONISATION ENERGY DECREASES down the Group Despite the increasing nuclear charge the values decrease due to the extra shielding provided by additional filled inner energy levels BeMgCaSr st I.E. / kJ mol -1 Ba nd I.E. / kJ mol -1 3rd I.E. / kJ mol -1 BERYLLIUM There are 4 protons pulling on the outer shell electrons 1st I.E. = 899 kJ mol 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 ©HOPTON

SUCCESSIVE IONISATION ENERGIES Successive Ionisation Energy values get larger BeMgCaSr st I.E. / kJ mol -1 Ba nd I.E. / kJ mol -1 3rd I.E. / kJ mol -1 ©HOPTON

SUCCESSIVE IONISATION ENERGIES Successive Ionisation Energy values get larger BeMgCaSr st I.E. / kJ mol -1 Ba nd I.E. / kJ mol -1 3rd I.E. / kJ mol st I.E. = 738 kJ mol -1 ©HOPTON

SUCCESSIVE IONISATION ENERGIES Successive Ionisation Energy values get larger BeMgCaSr st I.E. / kJ mol -1 Ba nd I.E. / kJ mol -1 3rd I.E. / kJ mol st I.E. = 738 kJ mol nd 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

Successive Ionisation Energy values get larger BeMgCaSr st I.E. / kJ mol -1 Ba nd I.E. / kJ mol -1 3rd I.E. / kJ mol st I.E. = 738 kJ mol nd 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

Successive Ionisation Energy values get larger BeMgCaSr st I.E. / kJ mol -1 Ba nd I.E. / kJ mol -1 3rd I.E. / kJ mol st I.E. = 738 kJ mol nd 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

CHEMICAL PROPERTIES OF THE ELEMENTS Reactivity increases down the Group due to the ease of cation formation OXYGENreact with increasing vigour down the group Mgburns readily with a bright white flame Mg(s) + O 2 (g) —> 2MgO(s) Baburns readily with an apple-green flame 2Ba(s) + O 2 (g) —> 2BaO(s) ©HOPTON

CHEMICAL PROPERTIES OF THE ELEMENTS Reactivity increases down the Group due to the ease of cation formation OXYGENreact with increasing vigour down the group Mgburns readily with a bright white flame Mg(s) + O 2 (g) —> 2MgO(s) Baburns readily with an apple-green flame 2Ba(s) + O 2 (g) —> 2BaO(s) In both cases… the metal is oxidisedOxidation No. increases from 0 to +2 oxygen is reducedOxidation No. decreases from 0 to -2 Mg —> Mg e¯ O + 2e¯—> O 2- ©HOPTON

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

CHEMICAL PROPERTIES OF THE ELEMENTS Reactivity increases down the Group due to the ease of cation formation WATERreact with increasing vigour down the group ©HOPTON

CHEMICAL PROPERTIES OF THE ELEMENTS Reactivity increases down the Group due to the ease of cation formation WATERreact with increasing vigour down the group Mgreacts very slowly with cold water Mg(s) + 2H 2 O(l) —> Mg(OH) 2 (aq) + H 2 (g) but reacts quickly with steam Mg(s) + H 2 O(g) —> MgO(s) + H 2 (g) ©HOPTON

CHEMICAL PROPERTIES OF THE ELEMENTS Reactivity increases down the Group due to the ease of cation formation WATERreact with increasing vigour down the group Mgreacts very slowly with cold water Mg(s) + 2H 2 O(l) —> Mg(OH) 2 (aq) + H 2 (g) but reacts quickly with steam Mg(s) + H 2 O(g) —> MgO(s) + H 2 (g) Bareacts vigorously with cold water Ba(s) + 2H 2 O(l) —> Ba(OH) 2 (aq) + H 2 (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 Bonding ionic solids; EXCEPT BeO which has covalent character BeO(beryllium oxide)MgO(magnesium oxide) CaO(calcium oxide)SrO(strontium oxide) BaO(barium oxide) Reaction with water ©HOPTON BeOMgOCaOSrO NONEreacts Reactivity with water BaO reacts Insoluble Sparingly soluble Slightly soluble Quite soluble Very soluble Solubility of hydroxide M(OH) 2 in water pH of 0.1M solution

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) Reaction with water React with water to produce the hydroxide (not Be) e.g.CaO(s) + H 2 O(l) —> Ca(OH) 2 (s) ©HOPTON BeOMgOCaOSrO NONEreacts Reactivity with water BaO reacts Insoluble Sparingly soluble Slightly soluble Quite soluble Very soluble Solubility of hydroxide M(OH) 2 in water pH of 0.1M solution

HYDROXIDES OF GROUP II Propertiesbasic strength also increases down group ©HOPTON

HYDROXIDES OF GROUP II Propertiesbasic strength also increases down group 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

HYDROXIDES OF GROUP II Propertiesbasic strength also increases down group 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(OH) 2 Mg(OH) 2 Ca(OH) 2 Sr(OH) 2 Ba(OH) 2 Insoluble Sparingly soluble Slightly soluble Quite soluble Very soluble Solubility in water pH of 0.1M solution

HYDROXIDES OF GROUP II Propertiesbasic strength also increases down group 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 Lower charge density of the larger Ca 2+ 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 Solubility in water pH of 0.1M solution

HYDROXIDES OF GROUP II Uses Ca(OH) 2 used in agriculture to neutralise acid soils Ca(OH) 2 (s) + 2H + (aq) —> Ca 2+ (aq) + 2H 2 O(l) Mg(OH) 2 used in toothpaste and indigestion tablets as an antacid Mg(OH) 2 (s) + 2H + (aq) —> Mg 2+ (aq) + 2H 2 O(l) Both the above are weak alkalis and not as caustic as sodium hydroxide ©HOPTON

CARBONATES OF GROUP II ©HOPTON

CARBONATES OF GROUP II Properties insoluble in water MgCO 3 CaCO 3 SrCO 3 BaCO x x x x Solubility g/100cm 3 of water ©HOPTON

CARBONATES OF GROUP II Properties insoluble in water undergo thermal decomposition to oxide and carbon dioxide e.g. MgCO 3 (s) —> MgO(s) + CO 2 (g) MgCO 3 CaCO 3 SrCO 3 BaCO x x x x Solubility g/100cm 3 of water Decomposition temperature / ºC ©HOPTON

CARBONATES OF GROUP II Properties insoluble in water undergo thermal decomposition to oxide and carbon dioxide e.g. MgCO 3 (s) —> MgO(s) + CO 2 (g) the ease of decomposition decreases down the group MgCO 3 CaCO 3 SrCO 3 BaCO x x x x Solubility g/100cm 3 of water Decomposition temperature / ºC ©HOPTON

CARBONATES OF GROUP II Properties insoluble in water undergo thermal decomposition to oxide and carbon dioxide e.g. MgCO 3 (s) —> MgO(s) + CO 2 (g) the ease of decomposition decreases down the group MgCO 3 CaCO 3 SrCO 3 BaCO x x x x Solubility g/100cm 3 of water Decomposition temperature / ºC EASIER HARDER ©HOPTON

CARBONATES OF GROUP II Properties insoluble in water undergo thermal decomposition to oxide and carbon dioxide e.g. MgCO 3 (s) —> MgO(s) + CO 2 (g) the ease of decomposition decreases down the group MgCO 3 CaCO 3 SrCO 3 BaCO x x x x Solubility g/100cm 3 of water Decomposition temperature / ºC One might think that the greater charge density of the smaller Mg 2+ would mean that it would hold onto the CO 3 2- ion more and the ions would be more difficult to separate. EASIER HARDER ©HOPTON

CARBONATES OF GROUP II Properties insoluble in water undergo thermal decomposition to oxide and carbon dioxide e.g. MgCO 3 (s) —> MgO(s) + CO 2 (g) the ease of decomposition decreases down the group MgCO 3 CaCO 3 SrCO 3 BaCO x x x x Solubility g/100cm 3 of water Decomposition temperature / ºC One might think that the greater charge density of the smaller Mg 2+ would mean that it would hold onto the CO 3 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 O 2- ion to make a more stable compound. EASIER HARDER ©HOPTON

MgSO 4 CaSO 4 SrSO 4 BaSO x x x x Solubility g/100cm 3 of water GROUP TRENDS SULFATES ©HOPTON

MgSO 4 CaSO 4 SrSO 4 BaSO x x x x Solubility g/100cm 3 of water 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

MgSO 4 CaSO 4 SrSO 4 BaSO x x x x Solubility g/100cm 3 of water 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 Greater charge density of Mg 2+ ion means that it is more attracted to water so the ionic lattice breaks up more easily ©HOPTON

MgSO 4 CaSO 4 SrSO 4 BaSO x x x x Solubility g/100cm 3 of water 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 Greater charge density of Mg 2+ ion means that it is more attracted to water so the ionic lattice breaks up more easily Lower charge density of larger Ca 2+ means that it is less attracted to water so the ionic lattice breaks up less easily – IT IS LESS SOLUBLE ©HOPTON

MgSO 4 CaSO 4 SrSO 4 BaSO x x x x Solubility g/100cm 3 of water 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 USEbarium sulfate’s insolubility is used as a test for sulfates Greater charge density of Mg 2+ ion means that it is more attracted to water so the ionic lattice breaks up more easily Lower charge density of larger Ca 2+ means that it is less attracted to water so the ionic lattice breaks up less easily – IT IS LESS SOLUBLE ©HOPTON

©2015 JONATHAN HOPTON & KNOCKHARDY PUBLISHING THE END AN INTRODUCTION TO GROUP II Alkaline earths ©HOPTON