Lecture Series 10 Transition Metal Chemistry Chapter 18 This is the last material that will be covered on the final Chapter 18 covers a huge amount of material in a very few number of pages Not only is there a lot of material in this chapter the nature of the material is nearly completely new at least on the surface There is simply no way that we can cover much of this chapter nor would we want to It is simply too much and I only have two days in which to lecture on this stuff Nevertheless there are a few important topics that we will cover This chapter concerns itself with the elements that exhibit the chemistry of the d orbitals These are called the transition metals Look for a moment at the fourth row of the periodic table which contains the elements shown in figure 1 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 4S 3D 4P th Figure 1 The 4 row of the periodic table The transition metals are the elements that range from Sc Scandium to Zn Zinc These elements exhibit a range of oxidation states that are unparalleled in the S and Pelements We briefly touched on oxidation states in previous sections but here is a formal definition The oxidation state of an atom is simply the charge on the atom For example Copper can exist as Cu Cuo Cu and Cu For these atoms and ions oxidation states are 1 0 1 and 2 respectively Often times students think that oxidation states must have something to do with the element oxygen This is not true Similarly an oxidation process also doesn t necessarily involve oxygen If an element is oxidized then its charge is increased in the positive direction Examples of oxidation processes include Cu Cu e Cuo Cu e Mn 3 Mn 7 4e A reduction process is the opposite of an oxidation process If an element is reduced then its charge is increased in the negative direction Any of the above examples of oxidation processes would be reduction processes if they were written in reverse such as for the first equation listed Cu e Cu This is related but is not quite the same as ionizing an atom such as we discussed back in Chapter 15 with the photoelectric effect In an oxidation reduction collectively called redox process if an atom or a molecule is oxidized then something else is reduced so that charge is balanced in the end Likewise if something is reduced then something else is oxidized Let s consider for a moment the electronic structure of Cu and try to understand these various oxidation states If we used the Aufbau principle Hund s rule Pauli principle etc we would say that the electronic structure of Cuo is 4S2 3D9 Now if we add one more electron we can get a closed shell or 4S2 3D10 This would be Cu and we would expect it to be fairly stable it is after all a closed shell anion Now imagine if we removed one electron from Cuo We would then have 4S2 3D8 This arrangement of electrons doesn t look especially remarkable and so one might not expect it to be very stable However try moving both of the 4S electrons into the D shell and you get 4S0 3D10 This is a closed shell cation and the electronic configuration now does look rather special In fact Cu is 4S0 3D10 and 1 is a common oxidation state for Cu Now let s consider Cu which would have an electronic configuration of 4S2 3D7 or of 4S0 3D9 depending on how we think about the 2 oxidation state Note that here I have been rather casual about moving the 4S electrons back and forth between the 3D orbitals In fact this is a fine thing to do and it is very common for transition metals to grab the S electrons for the d orbitals when some special stability can be gained However for this Cu species it is rather difficult to understand why either of these two electronic configurations would be particularly stable In fact Cu does exist but it is not as common as the other oxidation states From our simple arguments we would predict that the three most common oxidation states of Cu would be Cu Cuo and Cu Cu would less common This is what is observed The preceding discussion of the oxidation states of copper highlights both the beauty and frustration of inorganic chemistry It would be great if we could just take the electronic configurations of the transition metal atoms in their various oxidation states and predict which ones will to be observed which ones will be the most stable etc The fact is that we can t do this However we can use the electronic configurations as a guide to which oxidation states will be most likely However lots of possibilities may be observed possibilities that we don t think of when we just look for magic electronic configurations What do we mean by magic electronic configurations Here are a few with accompanying explanations The ones highlighted in red are especially stable 4S0 3D0 4S2 3D0 4S0 3D5 4S1 3D5 4S2 3D5 4S0 3D10 4S2 3D10 rare gas configuration ex Sc 2 Ti 4 Mn 7 closed S shell ex Ti II V III Mn V filled D shell ex Fe 3 Mn 2 6 unpaired aligned electrons example Cro V Fe 2 closed S shell aligned and unpaired electrons in D shell ex Co 2 Ni 3 closed D Shell Cuo Ago Auo closed S shell closed D Shell ex Hgo Cdo Zno Note that we have in a few cases referred to the oxidation states of the various elements using Roman numerals such as Mn V This is equivalent to Mn 5 and is actually a more common way of representing the 5 oxidation state of Manganese We will use Roman numerals throughout this discussion to represent positive oxidation states of transition metals Note also that in some instances the system that represents the magic configuration is a neutral atom such as Cro for 4S1 3D5 In fact in those cases the bare metal is very stable Recall that Cr provides a shiny metallic plating on many automotive parts or that mercury Hgo 6S2 5D10 is a stable metal that is used in thermometers and elsewhere Note also that there are many examples of magic configurations that are not found You can figure this out by comparing the above list with Figure 18 4 p 663 of the text For 4S1 3D5 one might expect Mn 1 In fact Mn 1 is not listed on 18 4 and so it is probably not very stable You ask Why not I am not really sure but I believe that it is because the Mn II state is so stable that any Mn I that you might form is immediately oxidized to Mn II Transition metal compounds Recall from our VSEPR theory that we had a number of shapes such as octahedral and square …