GROUP II CONTENTS ©HOPTON 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 ©HOPTON

GROUP PROPERTIES • all have the electronic configuration ... ns2 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

THE s-BLOCK ELEMENTS Li Na K Rb Cs Fr 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. ALKALI METALS Gp I Li 1s2 2s1 Na 1s2 2s2 2p6 3s1 K 1s2 2s2 2p6 3s23p64s1 Rb … 5s1 Cs … 6s1 Fr ©HOPTON

THE s-BLOCK ELEMENTS Li Be Na Mg K Ca Rb Sr Cs Ba Fr Rn 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. ALKALI METALS ALKALINE EARTHS Gp I Gp II Li Be 1s2 2s1 1s2 2s2 Na Mg 1s2 2s2 2p6 3s1 1s2 2s2 2p6 3s2 K Ca 1s2 2s2 2p6 3s23p64s1 1s2 2s2 2p6 3s23p64s2 Rb Sr … 5s1 … 5s2 Cs Ba … 6s1 … 6s2 Fr Rn ©HOPTON

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

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

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

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

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

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

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

GROUP TRENDS ATOMIC & IONIC RADIUS ©HOPTON 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 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 ATOMIC & IONIC RADIUS IONIC RADIUS INCREASES down Group 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 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 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 ©HOPTON

GROUP TRENDS ATOMIC & IONIC RADIUS IONIC RADIUS INCREASES down Group 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 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 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 1s2 2s2 2p6 3s2 1s2 2s2 2p6 1s2 2s2 2p6 3s23p64s2 1s2 2s2 2p6 3s23p6

GROUP TRENDS ATOMIC & IONIC RADIUS IONIC RADIUS INCREASES down Group 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 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 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

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

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

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

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

Larger ions mean that the electron cloud doesn’t bind them as strongly GROUP TRENDS MELTING POINT Be Mg Ca Sr Ba Melting point / ºC 1283 650 850 770 710 Electronic config. 2,2 2,8,2 2,8,8,2 2,8,18,8,2 2,8,18,18,8,2 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 Larger ions mean that the electron cloud doesn’t bind them as strongly ©HOPTON

Larger ions mean that the electron cloud doesn’t bind them as strongly GROUP TRENDS ©HOPTON MELTING POINT Be Mg Ca Sr Ba Melting point / ºC 1283 650 850 770 710 Electronic config. 2,2 2,8,2 2,8,8,2 2,8,18,8,2 2,8,18,18,8,2 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) Larger ions mean that the electron cloud doesn’t bind them as strongly

Explaining the decrease in first ionisation energy Ionisation 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 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 ©HOPTON

FIRST 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 ©HOPTON

FIRST 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 4+ BERYLLIUM There are 4 protons pulling on the outer shell electrons 1st I.E. = 899 kJ mol-1 ©HOPTON

FIRST 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 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 BERYLLIUM There are 4 protons pulling on the outer shell electrons 1st I.E. = 899 kJ mol-1 ©HOPTON

FIRST IONISATION ENERGY ©HOPTON 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 ©HOPTON

Variation of first ionization energy down a group (II) G-I G-II

SUCCESSIVE IONISATION ENERGIES 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 Successive Ionisation Energy values get larger ©HOPTON

SUCCESSIVE IONISATION ENERGIES 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 Successive Ionisation Energy values get larger 12+ 1st I.E. = 738 kJ mol-1 ©HOPTON

SUCCESSIVE IONISATION ENERGIES 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 Successive Ionisation Energy values get larger 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. ©HOPTON

SUCCESSIVE IONISATION ENERGIES 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 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. ©HOPTON

SUCCESSIVE IONISATION ENERGIES 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 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. ©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 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

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

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 WATER react with increasing vigour down the group ©HOPTON

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

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 Magnesium reacts with cold water exreamly slow Strontium reacts vigorously with cold water

CHEMICAL PROPERTIES OF THE ELEMENTS 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

Alkaline earth metals reacts with oxygen 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)

The reaction of heated magnesium with steam is faster than the reaction of magnesium with cold water. This is mainly because A 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 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

Reactions of the oxides with water 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 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 stop SrO + H2SO4 SrSO4(s) + H2O This is due to insoluble CaSO4 & SrSO4 covers the oxide. ( passive action)

Solubility of hydroxide g/100cm3 of water 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 Be Mg Ca Sr NONE reacts Reactivity with water Ba Insoluble Sparingly soluble Slightly Quite Very - 9-10 Solubility of hydroxide g/100cm3 of water pH of solution ©HOPTON

Solubility of hydroxide g/100cm3 of water 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) + H2O(l) —> Ca(OH)2(s) Be Mg Ca Sr NONE reacts Reactivity with water Ba Insoluble Sparingly soluble Slightly Quite Very - 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

HYDROXIDES OF GROUP II Properties basic 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

Solubility of hydroxide in water HYDROXIDES OF GROUP II Properties basic 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 Be Mg Ca Sr NONE reacts Reactivity with water Ba Insoluble Sparingly soluble Slightly Quite Very - 9-10 Solubility of hydroxide in water pH of solution ©HOPTON

Solubility of hydroxide in water HYDROXIDES OF GROUP II ©HOPTON Properties basic 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 Be Mg Ca Sr NONE reacts Reactivity with water Ba Insoluble Sparingly soluble Slightly Quite Very - 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.

Both the above are weak alkalis and not as caustic as sodium hydroxide HYDROXIDES OF GROUP II 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

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

Solubility g/100cm3 of water GROUP TRENDS SULPHATES MgSO4 CaSO4 SrSO4 BaSO4 3.6 x 10-1 1.1 x 10-3 6.2 x 10-5 9.0 x 10-7 Solubility g/100cm3 of water ©HOPTON

Solubility g/100cm3 of water GROUP TRENDS SULPHATES MgSO4 CaSO4 SrSO4 BaSO4 3.6 x 10-1 1.1 x 10-3 6.2 x 10-5 9.0 x 10-7 Solubility g/100cm3 of water 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

Solubility g/100cm3 of water GROUP TRENDS SULPHATES MgSO4 CaSO4 SrSO4 BaSO4 3.6 x 10-1 1.1 x 10-3 6.2 x 10-5 9.0 x 10-7 Solubility g/100cm3 of water 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 Mg2+ ion means that it is more attracted to water so the ionic lattice breaks up more easily ©HOPTON

Solubility g/100cm3 of water GROUP TRENDS SULPHATES MgSO4 CaSO4 SrSO4 BaSO4 3.6 x 10-1 1.1 x 10-3 6.2 x 10-5 9.0 x 10-7 Solubility g/100cm3 of water 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 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 Greater charge density of Mg2+ ion means that it is more attracted to water so the ionic lattice breaks up more easily ©HOPTON

Solubility g/100cm3 of water GROUP TRENDS SULPHATES MgSO4 CaSO4 SrSO4 BaSO4 3.6 x 10-1 1.1 x 10-3 6.2 x 10-5 9.0 x 10-7 Solubility g/100cm3 of water 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 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 Greater charge density of Mg2+ ion means that it is more attracted to water so the ionic lattice breaks up more easily ©HOPTON

Solubility g/100cm3 of water Decomposition temperature / ºC CARBONATES OF GROUP II ©HOPTON 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 Solubility g/100cm3 of water 1.5 x 10-4 1.3 x 10-5 7.4 x 10-6 9.1 x 10-6 Decomposition temperature / ºC 400 980 1280 1360 EASIER HARDER One might think that the greater charge density of the smaller Mg2+ would mean that it would hold onto the CO32- 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.

Thermal decomposition of metal carbonates 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 ion Now imagine what happens when this ion is placed next to a positive ion. The positive ion attracts the delocalised electrons in the carbonate ion towards itself. The carbonate ion becomes polarised.

Effect of sizes of cations on thermal stability of compounds +2 Metal carbonate Decomposition temperature C BeCO3 100 MgCO3 540 CaCO3 900 SrCO3 1280 BaCO3 1360 o +2 +2 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

The effect of heat on the Group 2 carbonates All 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 decompose XCO3(s) XO(s) + CO2(g) The carbonates become more stable to heat as you go down the group.

The delocalised electrons are pulled towards the positive ion. This end of the ion is on its way to breaking away and becoming carbon dioxide 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 o 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

2X(NO3)2(s) 2XO(g) + 4NO2(g) + O2(g) 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 will cause less distortion to nearby negative ions.

The effect of heat on the Group 2 nitrates All 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 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 is MCO3(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 Measurement : Measure Time for the limewater to turn milky Things to make the experiment fair Constant Bunsen lame/electrical heater setting Fixed height of test tube above the flame  Fixed volume/amount/mass of limewater

(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.

Group I element Flame colour Group II element Characteristic Properties of the s-Block Elements Group I element Flame colour Group II element Li Na K Rb Cs Deep red Golden yellow Lilac Bluish red Blue Ca Sr Ba Mg Brick red Blood red or crimson Green No 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 4d n = 4 4p 3d n = 3 4s e- 3p energy 3s 4s 2p n = 2 2s n =1 e- 1s

Compounds containing lithium, sodium, potassium, calcium and barium can be recognised by burning the compound and observing the colours produced: Sodium Yellow Strontium crimson Barium Green Lithium Red Potassium Lilac Calcium Brick red

Moving down group 2 the following properties decreases * Melting temperatures * Polarization power of cation * Ionisation energy Be Mg Ca Sr Ba Gp II Moving down group 2 the following properties increases * Atomic and ionic radii * Thermal stability of the compounds * Reactivity of the metal

Li Na K Rb Cs Li + 2H2O (l)  2LiOH(aq) + H2 (g) K + Cl2 (g)  2KCl(s) Gp I Li Na H2O(l) Cl2 (g) Colorless Ionic chlorides M+ Cl – The clorides are soluable in water forming colorless solution Metal Hydroxide + H2 K Rb Cs Li + 2H2O (l)  2LiOH(aq) + H2 (g) K + Cl2 (g)  2KCl(s)

Summary of gr II metal reactions Metal Halides Reactivity increases down the group Be/BeO Mg Ca Sr Ba Gp II (white ionic chlorides) * Berylium forms a covalent anhydrous chloride with low melting point Halogens No reaction H2O (l) Metal hydroxide H2O Metal Oxide + H2 H2O(g) Except BeO Metal Oxide Dilute acids Metal Hydroxide + H2 H2O(l) O2 (Basic Oxides) * BeO is amphoteric Dilute acids Salt + H2O * 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 * Dilute acids example: HCl or HNO3

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 Magnesium reacts with cold water exreamly slow Strontium reacts vigorously with cold water

Reaction flow chart for Calcium metals H2O 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) 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 Thermal stability decreases as : Atomic radius decrease As charge increase More polarization of Nitrate ion Flow chart Be Gp I Mg Ca Sr Ba Li Na K Rb Cs Gp II D Metal Oxides + NO2 + O2 Metal Nitrates + O2 Thermal stability increases Going 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 decomposition of Group I and Group II Nitrates D 2NaNO3 2NaNO2 + O2 D 2LiNO3 2Li2O + 4NO2 + O2 D 2Mg(NO3) 2 2MgO(s) + 4NO2 (g) + O2 (g)

Explain why potassium nitrate and calcium nitrate decompose to form different Products??  Calcium ions have greater positive charge (than potassium ions) or calcium ions are smaller (than potassium ions) Calcium (ions) more polarising or cause greater distortion Of nitrate (ion) / anion

Thermal stability of Group I and Group II Carbonates Thermal stability decreases as : Atomic radius decrease As charge increase More polarization of Nitrate ion Flow chart Be Gp I Mg Ca Sr Ba Li Na K Rb Cs Gp II D 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 decomposition of Group I and Group II Carbonates D Li2CO3 Li2O + CO2 D CaCO3 (s) CaO (s) + CO2

 All group 1 compounds are soluble. Solubility of Sulfates of group 2 decreases down the group  Hydroxides of group 2 increases down the group