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Periodicity (AHL)

Periodicity (AHL). Year 11 DP Chemistry Rob Slider. Oxides of Period 3. What patterns are there in the following properties? Structure Melting/boiling points Electrical conductivity Acidity. Oxide structure. Oxide melting/boiling points. Oxide electrical conductivity. Oxide acidity.

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Periodicity (AHL)

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  1. Periodicity (AHL) Year 11 DP Chemistry Rob Slider

  2. Oxides of Period 3 • What patterns are there in the following properties? • Structure • Melting/boiling points • Electrical conductivity • Acidity

  3. Oxide structure

  4. Oxide melting/boiling points

  5. Oxide electrical conductivity

  6. Oxide acidity Na2O(s) + H2O(l)  2Na+(aq) + 2OH-(aq) SiO2(s) + 2NaOH(aq)  Na2SiO3(aq) + H2O(l) SO2(g) + H2O(l)  H2SO3(aq) P4O10(s) + 6H2O(l) 4H3PO4(aq) Cl2O7(s) + H2O(l)  2HClO4(aq) Al2O3(s) + 6HCl(aq)  2AlCl3(aq) + H2O(l) Al2O3(s) + 2NaOH(aq) +3 H2O(l) 2NaAl(OH)4(aq)

  7. Chlorides of period 3 • What patterns are there in the following properties? • Structure • Melting/boiling points • Electrical conductivity • Acidity

  8. Chloride structure

  9. Chloride melting/boiling points

  10. Chloride electrical conductivity

  11. Chloride acidity NaCl(aq)  2Na+(aq) + 2Cl-(aq) Cl2(g) + H2O(l)  HCl(aq) + HClO(aq) AlCl3(s) + 3H2O(l)  Al2O3(aq)+ 6HCl(aq) SiCl4(s) + 4H2O(l)  Si(OH)4(aq) + 4HCl(aq)

  12. First row d-block The d-block elements are in the middle of the Periodic Table and include the transition metals. Starting in period 4 after the 4s fills, the 3d subshell begins to fill with electrons A transition metal (TM) is an element that has at least one ion with a partially filled d-subshell.Not all d-block elements are TM. Sc and Zn are not considered to be TM (more later...)

  13. Properties of TM Due to the partially filled d-subshell, TM have unique properties including: • Multiple oxidation states • Complex ion formation • Formation of coloured compounds • Catalytic properties

  14. Electronic configurations As we have seen previously, the configurations of the first row d-block mostly fill the 3d subshell in order. The exceptions come from Cr and Cu where we see more stable configurations from the half-filled and filled 3d subshell. This is possible because the 4s and 3d subshells are so similar in energy

  15. Sc and Zn (not TM) Sc forms Sc3+ which has the stable configuration of Ar Sc3+ has no 3d electrons, therefore it is not considered to be a TM Zn has a configuration of [Ar]3d104s2, The Zn2+ ion ([Ar] 3d10), therefore is not a typical TM ion

  16. Variable oxidation states +2 All transition metals can form the oxidation state of +2 due to the loss of the two s-electrons. In the first row, the 4s. This is because the 4s fills first, but when ions are being formed, the 4s electrons are also lost first. Examples: To write the electronic structure for Co2+: Co [Ar] 3d74s2 Co2+ [Ar] 3d7 The 2+ ion is formed by the loss of the two 4s electrons To write the electronic structure for V3+: V [Ar] 3d34s2 V3+ [Ar] 3d2 The 4s electrons are lost first, then one of the 3d electrons

  17. Variable oxidation states Due to the similar energy levels of the 4s and 3d, other oxidation states in addition to +2 are also possible. Cu also forms +1 due to the formation of the stable [Ar]3d10

  18. In the middle V, Cr, Mg, Fe It requires too much energy to remove all of the electrons from these elements as the number of valence electrons and high nuclear charge increases. What often occurs is the formation of more stable oxyanions, such as VO3-, vanadate(V). Some important ones to remember:

  19. Summary of oxidation states Boxed states are the important ones to know

  20. Summary of 1st d-block OS • Higher OS’s become less stable relative to lower ones on moving from left to right across the series(stronger + nuclear force) On the right, +2 is more common;+3 state highly oxidising. E.g. Co3+ is a strong oxidising agent (gain e- easily), Ni3+ & Cu3+ do not exist in aqueous solution. • On the left, +2 state highly reducing. • e.g. V2+(aq) , Cr2+(aq) are strong reducing agents (lose e- easily) • Compounds containing TM’s in high OS’s tend to be oxyanions and oxidising agents e.g. MnO4-

  21. Complex ion formation Complex ions have a metal ion at the centre with a number of other molecules or ions surrounding it. The bonds are coordinate bonds where a lone pair on a molecule/ion is donated to a low energy, unfilled metal orbital such as a d-orbital. These molecules/ions are called ligands. These are some common ligands found in complex ion formation. Notice they all have lone pairs of electrons Ligands are neutral molecules or anions that contain a non-bonding pair of electrons

  22. Complex ions Coordination number: The most common complex ions contain 4 or 6 ligands. These are known as 4-coordinated and 6-coordinated. 2 is also possible. The charge on the complex is the sum of the metal and the ligands. The Cr is 2+ and the water is neutral leading to a 2+ complex ion charge. Water forms hexahydrated complex ions (6-coordinated) with most transition metals. Example: [Fe(H2O)6]3+ Many complex ions form coloured solutions • You try: • Fe(III) + CN- (6-coord) • Cu (II) + Cl- (4-coord) • Ag+ + NH3 (2-coord)

  23. Complex ion geometry 2-coord complexes form linear geometries 4-coord complexes form tetrahedral or square planar geometries 6-coord complexes tend to form octahedral geometries

  24. Complex compounds Complex ions can be anions or cationsand will bond with oppositely charged ions to make salts. Notice how [Cu(NH3)4]2+ is formed: (CuCl4)2- is an anion that can form a compound with K+ to form [K2(CuCl4)] Would you expect these two compounds to be soluble in water? This complex ion can then bond with Cl- to form [Cu(NH3)4]Cl2 Yes, they are soluble in water.

  25. How does the metal attract so many ligands?? You may be wondering why a metal ion will attract more ligands than it has charges. +2 should attract -2 and +3 should attract -3, right?? Let’s look at an example: Fe(H2O)63+ Fe: 1s22s22p63s23p63d64s2 Fe3+:1s22s22p63s23p63d5 In Fe3+, the 4s is now empty and there are 5 unpaired e-. You might expect 5 ligands, but the ion uses six orbitals from the 4s, 4p and 4d to accept lone pairs from six water molecules. It hybridises six new orbitals all with the same energy. Why not 4 or 8? Six is the maximum number of water molecules it is possible to fit around an iron ion (and most other metal ions). By making the maximum number of bonds, it releases most energy and so becomes most energetically stable.

  26. Isomers (cis,trans) Metal complexes sometimes have more than one type of ligand attached. This leads to possible isomerism with complexes having different ligand arrangements. These are called stereoisomers. cis When ligands are adjacent to each other they are said to be cis- trans When ligands are opposite to each other they are said to be trans- cis-[CoCl2(NH3)4]+ trans-[CoCl2(NH3)4]+

  27. Optical isomers Some isomers are mirror images of one another. Therefore, they cannot be superimposed on one another. These two mirror image compounds are known as optical isomers or enantiomers.

  28. Coloured complexes Many d-complexes are coloured. These characteristic colours are specific to individual ions and depend upon: • Metal oxidation state • Ligands attached • Coordination number/shape Same metal/different OS Same metal/different ligand Same metal/different coord

  29. Why coloured? d,d transitions The d-orbitals shown above, have various arrangements around the x, y and z axes. When a 6-coord complex is formed with a d-block element, the ligands will approach along the axes of an octahedral, to minimise repulsions of bonding e-. The approach of the ligands raises the energy level of the d-orbitals, but the orbitals that lie on the axes (4,5 above) will experience more repulsion and thus will be a slightly higher energy level (than 1,2,3). This means the d orbitals are split.

  30. d,d transitions Movement between the d-orbitals by the e- represents an energy change, ΔE. RememberingΔE=hv, a transition between d-orbitals represents a specific frequency that is specific to a complex. Considering the four d-block elements above, only 2 and 3 have possible transitions. They are coloured due to the excitation of e- to higher d-orbitals. This transition absorbs specific frequencies and we perceive the remaining frequencies. Why are Sc3+ and Zn2+ colourless?

  31. Hexa-aqua complex colours This shows the colours of 6-coord aqua complexes of the first row d-block. Exceptions are Cu(I) which only forms simple colourless compounds and Cu(II) which forms a 4-coord aqua complex [Cu(H2O)4]2+ . Notice there are no possible transitions for Sc3+ and Zn2+, so they are typically colourless.

  32. Complex colours-examples

  33. TM as catalysts • Transition metals and their compounds function as catalysts due to: • their ability to change oxidation state • In the metal’s ability to adsorb other substances on to their surface and activate them in the process. Iron in the Haber Process The Haber Process combines hydrogen and nitrogen to make ammonia using an iron catalyst. Nitrogen and hydrogen molecules are adsorbed on to the metallic iron surface. The hydrogen almost immediately splits into its component atoms by sharing or exchanging electrons with the catalyst surface

  34. Catalyst examples V2O5 in the Contact Process This is the conversion of sulfur dioxide to sulfur trioxide by passing the gaseous reactants over a solid vanadium (V) oxide MnO2 in the decomposition of hydrogen peroxide This speeds up the spontaneous decomposition of hydrogen peroxide by manganese (IV) oxide Enzymatic catalysis Fe in haemoglobin for carrying oxygen Co in vitamin B12 to help produce red blood cells See (Green, p92 for structures) Nickel in the hydrogenation of C=C bonds This reaction see the conversion of alkenes to alkanes Catalytic converters Pt and Pd are used to convert NOx and CO to harmless gases

  35. Economic significance of Contact Process The Contact Process is used in the manufacture of sulfuric acid. Sulfuric acid is used in many industrial processes such as the manufacture of polymers, fertilisers and detergents. It is also used in mining and petrochemicals industries. Many experts point to the amount of sulfuric acid production as a good indication of the health of a country’s chemical industry. The more healthy the chemical industry, the more healthy industry is in general.

  36. Economic significance of Haber Process The Haber Process is the production of ammonia from it’s gaseous elements. Ammonia is important to an economy for many reasons. This demonstrates a country’s ability to take readily available raw materials and turn them into useful products. Importantly, it is used in fertilisers which is vital in helping to feed the populations. It is also used in the manufacture of explosives. Developed during WWI, this helped Germany prolong the war. It is also used in the production of polymers such as nylon, which is used to make a variety of materials from clothing to toothbrushes to parachutes.

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