Properties of p-Block Elements

The main source of boron is a complex compound of boron called borax. About half of the world supply of borax comes from a large deposit in California s Mojave Desert. Borax is used as a cleaning agent and as fireproof insulation. Another compound of boron, boric acid, is used as a disinfectant and as an eye wash. A form of boron nitride is the second hardest known material only diamond is harder. These materials are classified as superabrasives. They are used in grinding wheels, which shape manufactured parts and tools. 

Based on the trends discussed in Chapter 6, the metallic properties of the elements in group 4A should increase as the atomic number increases. Carbon is a nonmetal silicon and germanium are metalloids tin and lead are metals. With such a wide range of properties, there are few rules that apply to all members of the group. One general trend does apply. The period-2 element, carbon, is not representative of the other elements within the group. 

The branch of chemistry that deals with all other compounds is called inorganic chemistry, meaning not organic. Carbonates, cyanides, carbides, sulfides, and oxides of carbon are classified as inorganic compounds. Geologists call these compounds minerals. A mineral is an element or inorganic compound that is found in nature as solid crystals. Minerals usually are found mixed with other materials in ores. An ore is a material from which a mineral can be removed at a reasonable cost. In other words, the cost of extraction cannot approach or exceed the economic value of the mineral. 

Although both diamond and graphite contain only carbon atoms, they display different properties. Graphite is one of the softest known materials diamond is one of the hardest. These different forms of the same element are 

The energy used to recycle aluminum is about 5% of the energy needed to extract aluminum from its ore. 

The elements of the p-block are in groups 3A through 8A and include metals, nonmetals, and metalloids. Many can form more than one type of ion. 

Group 4A also contains the metalloids silicon and germanium and the metals tin and lead. Silicon, the second most abundant element in Earth s crust, is most often combined with oxygen in silica, which is found in quartz, sand, and glass. Alloys of tin such as bronze are mainly used for decorative items. Lead was one of the first metals obtained from its ore and had many uses until it was determined to be toxic. The major current use of lead is in automobile storage batteries. 

Find the following pairs of elements in the periodic table. State the name of each. Then compare them in terms of group number and number of valence electrons. Identify each element as a metal, non-metal, or metalloid. Also state a use for each element. 

Both C, carbon, and Pb, lead, are in group 4A and have foixr valence electrons. Carbon is a nonmetal. In its graphite form, it is used in pencils. Lead is a toxic metal used in automobile storage batteries. 

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The d-block transition metals, which form a group of elements ten-wide and four-deep in the Periodic Table associated with filling of the five d orbitals, represent the classical metals of coordination chemistry and the ones on which there is significant and continuing focus. In particular, the lighter and usually more abundant or accessible elements of the first row of the d block are the centre of most attention. Whereas stable oxidation states of p-block elements correspond dominantly to empty or filled valence shells, the d-block elements characteristically exhibit stable oxidation states where the nd shell remains partly filled it is this behaviour that plays an overarching role in the chemical and physical properties of this family of elements, as covered in earlier chapters. 

Generally speaking, the mechanisms of p-block element reactions are not particularly consistent with the rules outlined above. The reason for this boils down to the so-called first-row anomaly, where both first- and second-period elements (H-Ne) are all somewhat unreasonably lumped together as first row. The expression means that the chemical properties of first-row elements are anomalous relative to those of their heavier congeners. Let us go through the above four rules one by one and see how well they hold up in a main-group inorganic context. 

All d-block elements are metals (Fig. 1.63). Their properties are transitional between the s- and the p-block elements, which (with the exception of the members of Group 12) accounts for their alternative name, the transition metals. Because transition metals in the same period differ mainly in the number of /-electrons, and these electrons are in inner shells, their properties are very similar. 

The very negative Ln t + /Ln potentials are consistent with the electropositive nature of the lanthanide elements their Allred-Rochow electronegativity coefficients are all 1.1 except for europium, which has a value of 1.0. The lighter elements of Group 3, Sc and Y, both have electronegativity coefficients of 1.3. The nearest p-block element to the lanthanides in these properties is magnesium (Mg2+/Mg) = -2.37 V, and its electronegativity coefficient is 1.2. 

This was developed by Linus Pauling in 1931 and was the first quantum-based model of bonding. It is based on the premise that if the atomic s, p, and d orbitals occupied by the valence electrons of adjacent atoms are combined in a suitable way, the hybrid orbitals that result will have the character and directional properties that are consistent with the bonding pattern in the molecule. The rules for bringing about these combinations turn out to be remarkably simple, so once they were worked out it became possible to use this model to predict the bonding behavior in a wide variety of molecules. The hybrid orbital model is most usefully applied to the p-block elements the first two rows of the periodic table, and is especially important in organic chemistry see Page 37. 

The electronic properties of most main group s- and p-block elements are better described by introducing a periodic potential as a small perturbation. In the context of the present model, this approach is known as the nearly-free-electron (NFE) model. In 1930, Peierls showed that, in the NFE limit, band gaps arise from electron diffraction, a natural consequence of wave propagation in a periodic structure (Peierls, 1930). Brillouin generalized the result and showed that, in three dimensions, the surfaces of discontinuity form polyhedra in reciprocal space-the BZ (Brillouin, 1930). 

Norman, Nicolas C. Periodicity and the p-Block Elements. Oxford Oxford University Press, 1994. This book describes group properties of post-transition metals, metalloids, and nonmetals. 

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