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AN INTRODUCTION TO GROUP II Alkaline earths

© HOPTON. AN INTRODUCTION TO GROUP II Alkaline earths. 2008 SPECIFICATIONS. KNOCKHARDY PUBLISHING. © HOPTON. KNOCKHARDY PUBLISHING. GROUP II (Alkaline Earths). INTRODUCTION

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AN INTRODUCTION TO GROUP II Alkaline earths

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  1. ©HOPTON AN INTRODUCTION TO GROUP II Alkaline earths 2008 SPECIFICATIONS KNOCKHARDY PUBLISHING

  2. ©HOPTON KNOCKHARDY PUBLISHING GROUP II (Alkaline Earths) 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... www.knockhardy.org.uk/sci.htm Navigation is achieved by... either clicking on the grey arrows at the foot of each page or using the left and right arrow keys on the keyboard

  3. ©HOPTON GROUP II • 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

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

  5. ©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.

  6. ©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. ALKALI METALS Gp I Li 1s22s1 Na 1s2 2s2 2p63s1 K 1s2 2s2 2p63s23p64s1 Rb … 5s1 Cs … 6s1 Fr

  7. ©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. ALKALI METALS ALKALINE EARTHS Gp I Gp II Li Be 1s22s1 1s22s2 Na Mg 1s2 2s2 2p63s1 1s2 2s2 2p63s2 K Ca 1s2 2s2 2p63s23p64s1 1s2 2s2 2p63s23p64s2 Rb Sr … 5s1 … 5s2 Cs Ba … 6s1 … 6s2 Fr Rn

  8. ©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. ALKALI METALS ALKALINE EARTHS Gp I Gp II Li Be 1s22s1 1s22s2 Na Mg 1s2 2s2 2p63s1 1s2 2s2 2p63s2 K Ca 1s2 2s2 2p63s23p64s1 1s2 2s2 2p63s23p64s2 Rb Sr … 5s1 … 5s2 Cs Ba … 6s1 … 6s2 Fr Rn Francium and radium are both short-lived radioactive elements

  9. ©HOPTON 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 1s22s2 …3s2 … 4s2 … 5s2 … 6s2

  10. ©HOPTON 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 1s22s2 …3s2 … 4s2 … 5s2 … 6s2 As the nuclear charge increases, the electrons go into shells further from the nucleus.

  11. ©HOPTON 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 1s22s2 …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

  12. Be Mg Ca Sr Ba Atomic radius / nm 0.106 0.140 0.174 0.191 0.198 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 ATOMIC & IONIC RADIUS

  13. Be Mg Ca Sr Ba Atomic radius / nm 0.106 0.140 0.174 0.191 0.198 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 ATOMIC & IONIC RADIUS 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 2p63s2 1s2 2s2 2p63s23p64s2

  14. Be Mg Ca Sr Ba Atomic radius / nm 0.106 0.140 0.174 0.191 0.198 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 ATOMIC & IONIC RADIUS 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 2p63s2 1s2 2s2 2p63s23p64s2 • 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 2p63s1 12 protons 1s2 2s2 2p63s2

  15. Be Mg Ca Sr Ba Atomic radius / nm 0.106 0.140 0.174 0.191 0.198 Electronic config. 2,2 2,8,2 2,8,8,2 2,8,18,8,2 2,8,18,18,8,2 Be2+ Mg2+ Ca2+ Sr2+ Ba2+ Ionic radius / nm 0.030 0.064 0.094 0.110 0.134 Electronic config. 2 2,8 2,8,8 2,8,18,8 2,8,18,18,8 ©HOPTON GROUP TRENDS ATOMIC & IONIC RADIUS

  16. Be Mg Ca Sr Ba Atomic radius / nm 0.106 0.140 0.174 0.191 0.198 Electronic config. 2,2 2,8,2 2,8,8,2 2,8,18,8,2 2,8,18,18,8,2 Be2+ Mg2+ Ca2+ Sr2+ Ba2+ Ionic radius / nm 0.030 0.064 0.094 0.110 0.134 Electronic config. 2 2,8 2,8,8 2,8,18,8 2,8,18,18,8 ©HOPTON GROUP TRENDS ATOMIC & IONIC RADIUS IONIC RADIUS INCREASES down Group • ions are smaller than atoms – on removing the outer shell electrons, the remaining electrons are now in fewer shells

  17. Be Mg Ca Sr Ba Atomic radius / nm 0.106 0.140 0.174 0.191 0.198 Electronic config. 2,2 2,8,2 2,8,8,2 2,8,18,8,2 2,8,18,18,8,2 Be2+ Mg2+ Ca2+ Sr2+ Ba2+ Ionic radius / nm 0.030 0.064 0.094 0.110 0.134 Electronic config. 2 2,8 2,8,8 2,8,18,8 2,8,18,18,8 ©HOPTON GROUP TRENDS ATOMIC & IONIC RADIUS 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 2p63s2 1s2 2s2 2p6

  18. Be Mg Ca Sr Ba Atomic radius / nm 0.106 0.140 0.174 0.191 0.198 Electronic config. 2,2 2,8,2 2,8,8,2 2,8,18,8,2 2,8,18,18,8,2 Be2+ Mg2+ Ca2+ Sr2+ Ba2+ Ionic radius / nm 0.030 0.064 0.094 0.110 0.134 Electronic config. 2 2,8 2,8,8 2,8,18,8 2,8,18,18,8 ©HOPTON GROUP TRENDS ATOMIC & IONIC RADIUS 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 2p63s2 1s2 2s2 2p6 1s2 2s2 2p63s23p64s2 1s2 2s2 2p63s23p6

  19. ©HOPTON 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

  20. ©HOPTON 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

  21. ©HOPTON 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

  22. ©HOPTON 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

  23. ©HOPTON 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 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

  24. ©HOPTON FIRST IONISATION ENERGY

  25. ©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

  26. ©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 DECREASESdown the Group Despite the increasing nuclear charge the values decrease due to the extra shielding provided by additional filled inner energy levels

  27. 4+ ©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 DECREASESdown the Group Despite the increasing nuclear charge the values decrease due to the extra shielding provided by additional filled inner energy levels BERYLLIUM There are 4 protons pulling on the outer shell electrons 1st I.E. = 899 kJ mol-1

  28. 4+ 12+ ©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 DECREASESdown the Group Despite the increasing nuclear charge the values decrease due to the extra shielding provided by additional filled inner energy levels 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

  29. 4+ 12+ ©HOPTON ©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 DECREASESdown the Group Despite the increasing nuclear charge the values decrease due to the extra shielding provided by additional filled inner energy levels 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

  30. ©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

  31. ©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

  32. ©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.

  33. ©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.

  34. ©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.

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

  36. ©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)

  37. ©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-

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

  39. ©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

  40. ©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)

  41. ©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) Ba reacts vigorously with cold water Ba(s) + 2H2O(l) —> Ba(OH)2(aq) + H2(g)

  42. ©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)

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

  44. Be Mg Ca Sr Ba Reactivity with water NONE reacts reacts reacts reacts Solubility of hydroxide g/100cm3 of water Insoluble Sparingly soluble Slightly soluble Quite soluble Very soluble pH of solution - 9-10 ©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 React with water to produce the hydroxide (not Be) e.g. CaO(s) + H2O(l) —> Ca(OH)2(s)

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

  46. ©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

  47. Be Mg Ca Sr Ba Reactivity with water NONE reacts reacts reacts reacts Solubility of hydroxide in water Insoluble Sparingly soluble Slightly soluble Quite soluble Very soluble pH of solution - 9-10 ©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

  48. Be Mg Ca Sr Ba Reactivity with water NONE reacts reacts reacts reacts Solubility of hydroxide in water Insoluble Sparingly soluble Slightly soluble Quite soluble Very soluble pH of solution - 9-10 ©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 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.

  49. ©HOPTON 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

  50. ©HOPTON CARBONATES OF GROUP II

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