Ionization energy of metals

Table 13. Ionization energies of metal olefin complexes1...

The energy required to remove a valence electron from an atom is called its ionization energy. Figure 11.17 in Section 11.6 shows that the ionization energies of metals are lower than the ionization energies of nonmetals. 

Boron is unique among the elements in the structural complexity of its allotropic modifications this reflects the variety of ways in which boron seeks to solve the problem of having fewer electrons than atomic orbitals available for bonding. Elements in this situation usually adopt metallic bonding, but the small size and high ionization energies of B (p. 222) result in covalent rather than metallic bonding. The structural unit which dominates the various allotropes of B is the B 2 icosahedron (Fig. 6.1), and this also occurs in several metal boride structures and in certain boron hydride derivatives. Because of the fivefold rotation symmetry at the individual B atoms, the B)2 icosahedra pack rather inefficiently and there... 

The location of the metals in the periodic table is shown in Figure 17-4. We see that the metals are located on the left side of the table, while the nonmetals are exclusively in the upper right corner. Furthermore, the elements on the left side of the table have relatively low ionization energies. We shall see that the low ionization energies of the metallic elements aid in explaining many of the features of metallic behavior. 

We have seen that the pure elements may solidify in the form of molecular solids, network solids, or metals. Compounds also may condense to molecular solids, network solids, or metallic solids. In addition, there is a new effect that does not occur with the pure elements. In a pure element the ionization energies of all atoms are identical and electrons are shared equally. In compounds, where the most stable electron distribution need not involve equal sharing, electric dipoles may result. Since two bonded atoms may have different ionization energies, the electrons may spend more time near one of the positive nuclei than near the other. This charge separation may give rise to strong intermolecular forces of a type not found in the pure elements. 

We have already mentioned that the stability of the metallic crystal and the ionization energies of the atom tend to increase in the series sodium, magnesium, and aluminum. In spite of this, aluminum is still an excellent reducing agent because the hydration energy of the Al+1 ion is very large (Table 20-III). 

The ionization energy of the sulfur atom shows that it is even more reluctant than phosphorus to lose electrons. The common compounds of sulfur are the sulfides, which may be formed by reactions of elemental sulfur with a large number of metals. Typical reactions are... 

Raghavachari, K., Trucks, G.W., Highly Correlated Systems, Ionization Energies of First Row Transition Metals Sc-Zn, Journal of Chemical Physics, 1989 91 2457-2460. 

The low ionization energies of elements at the lower left of the periodic table account for their metallic character. A block of metal consists of a collection of cations of the element surrounded by a sea of valence electrons that the atoms have lost (Fig. 1.53). Only elements with low ionization energies—the members of the s block, the d block, the f block, and the lower left of the p block—can form metallic solids, because only they can lose electrons easily. 

The first ionization energy is highest for elements close to helium and is lowest for elements close to cesium. Second ionization energies are higher than first ionization energies (of the same element) and very much higher if the electron is to be removed from a closed shell. Metals are found toward the lower left of the periodic table because these elements have low ionization energies and can readily lose their electrons. 

Elements on the left of the p block, especially the heavier elements, have ionization energies that are low enough for these elements to have some of the metallic properties of the members of the s block. However, the ionization energies of the p-block metals are quite high, and they are less reactive than those in the s block. The elements aluminum, tin, and lead, which are important construction materials, all lie in this region of the periodic table (Fig. 1.61). 

Self-Test 16.1A Predict trends in ionization energies of the d-block metals. 

The first ionization energies of transition metals show gradual upward trends across each row of the periodic table. 

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