Group 12 Zinc, Cadmium, and Mercury

The (/-block elements tend to lose their valence s-electrons when they form compounds. Most of them can also lose a variable number of d-electrons and show variable valence. The only elements of the block that do not use their (/-electrons in compound formation are the members of Group 12 (zinc, cadmium, and mercury). The ability to exist in different oxidation states is responsible for many of the special properties of these elements and plays a role in the action of many vital biomolecules (Box 16.1). 

Group 12 zinc, cadmium and mercury (G4) Complexes structure and isomerism (H6)... 

Group 11 Copper, Silver, and Gold 23-7 Group 12 Zinc, Cadmium, and Mercury... 

The elements in Groups 3 through 11 are called the transition metals because they represent a transition from the highly reactive metals of the s block to the much less reactive metals of Group 12 and the p block (Fig. 16.1). Note that the transition metals do not extend all the way across the d block the Group 12 elements (zinc, cadmium, and mercury) are not normally considered to be transition elements. Because their d-orbitals are full, the Group 12 elements have properties that are more like those of main-group metals than those of transition metals. Just after... 

Of the Group 12 elements, zinc, cadmium and mercury, only Hg has a water-stable -I-1 state, and all three elements have + 2 states that are water-stable. Their reduction potentials are summarized in the Latimer diagram ... 

Group 12 In order of increasing atomic number, ihese are zinc, cadmium, and mercury, The eleiiieuls of this group are characterized by the presence ol two electrons in an outer shell Although mercury also has a valence of I -l, all of the elements in this, group have a 7+ valence in common. 

The elements zinc, cadmium, and mercury, which have two electrons outside filled penultimate d shells, are classed in Group 12. Although the difference between the calcium and zinc subgroups is marked, zinc, and to a lesser extent cadmium, show some resemblance to beryllium or magnesium in their chemistry. We discuss these elements separately (Chapter 15), but note here that zinc, which has the lowest second ionization enthalpy in the Zn, Cd, Hg group, still has a value (1726 kJ mol-1) similar to that of beryllium (1757 kJ mol"1), and its standard potential (-0.76 V) is considerably less negative than that of magnesium. 

The Group 12 metals, zinc, cadmium, and mercury, have valence electron configurations of n - )d Zinc and, to a lesser extent, cadmium resemble beryllium or magnesium in their chemistry. 

In fact, the classification of chemical elements is valuable only in so far as it illustrates chemical behaviour, and it is conventional to use the term transition elements in a mote restricted sense. The elements in the irmer transition series from cerium (58) to lutetium (71) are called the lanthanoids those in the series from thorium (90) to lawrencium (103) are the actl-noids. These two series together make up the /block in the periodic table. It is also common to include scandium, yttrium, and lanthanum with the lanthanoids (because of chemical similarity) and to include actinium with the actinoids. Of the remaining transition elements, it is usual to speak of three main transition series from titanium to copper from zirconium to silver and from hafnium to gold. All these elements have similar chemical properties that result from the presence of unfilled d-orbltals in the element or (in the case of copper, silver, and gold) in the ions. The elements from 104 to 109 and the undiscovered elements 110 and 111 make up a fourth transition series. The elements zinc, cadmium, and mercury have filled d-orbltals both in the elements and in compounds, and are usually regarded as nontransition elements forming group 12 of the periodic table. 

The equilibrium structures of the dihalides of the Group 12 metals zinc, cadmium and mercury all appear to be linear or nearly so in no case has an angular structure been proven. The difference between the dihalides of Ca and Zn, between Sr and Cd and between Ba and Hg suggests an explanation of the bent equilibrium stmctures in terms of the vacant valence shell d orbitals of the Group 2 metals. 

---