Periodic tables influence

That the position of an element in the Periodic Table influences its chemistry is inevitable, and a consequence of the Periodic Table reflecting the electronic configuration of the element. However, it is less clearly recognized that elements within the same column (and hence with the same valence shell electron set) differ in their chemistry. It is instructive to overview the chemical impact of the central atom to illustrate both similarities and differences. These, along with specific examples of synthetic coordination chemistry, appear in Chapter 6, whereas shape and stability aspects are detailed in the next two chapters. 

Core Metal Chemistry - Periodic Table Influences... 

Consider the fluorides of the second-row elements. There is a continuous change in ionic character of the bonds fluorine forms with the elements F, O, N, C, B, Be, and Li. The ionic character increases as the difference in ionization energies increases (see Table 16-11). This ionic character results in an electric dipole in each bond. The molecular dipole will be determined by the sum of the dipoles of all of the bonds, taking into account the geometry of the molecule. Since the properties of the molecule are strongly influenced by the molecular dipole, we shall investigate how it is determined by the molecular architecture and the ionic character of the individual bonds. For this study we shall begin at the left side of the periodic table. 

The last vertical column of the eighth group of the Periodic Table of the Elements comprises the three metals nickel, palladium, and platinum, which are the catalysts most often used in various reactions of hydrogen, e.g. hydrogenation, hydrogenolysis, and hydroisomerization. The considerations which are of particular relevance to the catalytic activity of these metals are their surface interactions with hydrogen, the various states of its adatoms, and admolecules, eventually further influenced by the coadsorbed other reactant species. 

The known oxidation states of plutonium present a 5f -series, starting from f1 [Pu(VII)] up to f5 [Pu(III)]. But contrary to the 4f - and 5f series across the period table, where the properties can be described by some smooth varying parameters, changing of the oxidation states influences the electronic properties drastically. Due to the large range of available oxidation states plutonium represents a favorable element among the actinides to study these effects. 

Cu, Ag, and Au are sd-metals (the d-band is complete but its top is not far from the Fermi level, with a possible influence on surface bond formation) and belong to the same group (I B) of the periodic table. Their scattered positions definitely rule out the possibility of making correlations within a group rather than within a period. Their AX values vary in the sequence Au < Ag < Cu and are quantitatively closer to that for Ga than for the sp-metals. This is especially the case ofCu. The values of AX have not been included in Table 27 since they will be discussed in connection with single-crystal faces. 

Finally, there are groups of liquid crystals where, at the current time, force fields are not particularly useful. These include most metal-containing liquid crystals. Some attempts have been made to generalise traditional force fields to allow them to cover more of the periodic table [40, 43]. However, many of these attempts are simple extensions of the force fields used for simple organic systems, and do not attempt to take into account the additional strong polarisation effects that occur in many metal-containing liquid crystals, and which strongly influence both molecular structure and intermolecular interactions. 

Another influence on the magnitude of the crystal field splitting is the position of the metal in the periodic table. Crystal field splitting energy increases substantially as valence orbitals change from 3 d to 4d to 5 d. Again, orbital shapes explain this trend. Orbital size increases as n increases, and this means that the d orbital set becomes... 

Figure 6.30. Position of the center of the d band for the three series of transition metals. Note that the d band center shifts down towards the right of the periodic table. When the d band is completely filled, it shifts further down and becomes, effectively, a core level with little influence on the chemical behavior of...

These problems have of course different weights for the different metals. The high reactivity of the elements on the left-side of the Periodic Table is well-known. On this subject, relevant examples based on rare earth metals and their alloys and compounds are given in a paper by Gschneidner (1993) Metals, alloys and compounds high purities do make a difference The influence of impurity atoms, especially the interstitial elements, on some of the properties of pure rare earth metals and the stabilization of non-equilibrium structures of the metals are there discussed. The effects of impurities on intermetallic and non-metallic R compounds are also considered, including the composition and structure of line compounds, the nominal vs. true composition of a sample and/or of an intermediate phase, the stabilization of non-existent binary phases which correspond to real new ternary phases, etc. A few examples taken from the above-mentioned paper and reported here are especially relevant. They may be useful to highlight typical problems met in preparative intermetallic chemistry. 

Formation of coordination complexes is typical of transition metals, but other metals also form complexes. The tendency to form complexes is a function of the metal s electron configuration and the nature of its outer electron orbitals. Metal cations can be classified into types A and B based on their coordination characteristics, as shown in Table 3.5. A-type cations, which tend to be from the left side of the Periodic Table, have the inert-gas type electron configuration with largely empty d-orbitals. They can be imagined as having electron sheaths not easily deformed under the influence of the electric fields around neighbouring ions. B-type cations have a more readily deformable electron sheath. 

The configuration of electrons around the nuclei of atoms is related to the structure of the periodic table. Chemical properties of elements are mainly determined by the arrangement of electrons in the outermost valence shells of atoms. (Other factors also influence chemical... 

The chemical behavior of the various elements is influenced more by the charge of their ion than by any other intrinsic property. In the periodic table (see Figure 3-3), elements in a column form analogous compounds because they have the same charge on their ions. 

The general trends across periods and down groups of the Periodic Table are influenced by relativistic effects, which become more serious in the heavier elements (Z > 55). This can only be dealt with here in a brief manner. 

Semiconductive elements Si and Ge (Group IVB or 13 in the periodic table) have become very important electronic materials since development of a purification method. The electronic properties of semiconductive elements of high purity can be controlled by the species and concentration of defects and impurity elements. On the other hand, in the case of semiconductive compounds, that is, III-V and II-VI compounds, we have to consider not only control of the purity of constituent elements but also the nonstoichiometry, both of which have much influence on the electronic properties. In this sense, control of the electrical properties of semiconductive compounds is more difficult than that of semiconductive elements. 

Correlations have been made between gas-phase ionization potentials of free ions and the redox potentials of isostructural [MXe]"" complexes of the elements of the same row of the periodic table (476). Despite the observation of such correlations, caution must be taken, because they ignore both cr and tt ligand field effects. The latter are often more important in influencing the relative oxidizing or reducing strength of complexes. 

C ls22s2p2 Si ls22s22p63s23p2). Because of the position of silicon in the third row of the Periodic Table, the chemistry of this element is influenced by the availability of empty 3d orbitals which are not greatly higher in energy than the silicon 3s and 3p orbitals. The availibility of low lying 3d orbitals to silicon and the possibility of their involvement in bond formation has been used to explain the easy formation of 5- and 6-coordinated silicon complexes, and the unexpected physical properties, stereochemistry, and chemical behaviour of a number of 4-coordinated silicon compounds. 

Electron spin has more subtle effects on atomic and molecular energies. The exclusion principle as stated above is really a consequence of a more profound influence of the spin on the way electrons move. Two elections with parallel spins (i.e. having the same value of ms) have a strong tendency to avoid each other in space. Suppose we put two elections into different orbitals. There is then no restriction on the relative spin directions. If they are parallel, however, the electrons keep apart and so the electrostatic repulsion between them is less than if the spins are anti-parallel. The former situation gives a lower total energy. We shall see below that this has consequences for the filling of degenerate orbitals, such as the p and d shells, in the periodic table. 

---