Periodic trends in metallic properties

In Sections 20.5, 20.6, and 20.7 we will study the chemistry of selected metals from Group lA (the alkali metals). Group 2A (the alkaline earth metals), and Group 3A (aluminum). 

As a group, the alkali metals (the Group lA elements) are the most electropositive (or the least electronegative) elements known. They exhibit many similar properties, some of which are listed in Table 20,4, From their electron configurations we expect the oxidation number of these elements in their compounds to be +1 because the cations would be isoelectronic with the noble gases. This is indeed the case. 

Note that this is a chemical rather than electrolytic reduction. 

The chemistry of lithium, rubidium, and cesium is less important all isotopes of francium, the last member of the group, are radioactive. 

Metallic sodium is most conveniently obtained from molten sodium chloride by electrolysis in the Downs cell (see Section 19.8). The melting point of sodium chloride is rather high (801°C), and much energy is needed to keep large amounts of the substance molten. Adding a suitable substance, such as CaCl2, lowers the melting point to about 600°C—a more convenient temperature for the electrolysis process. 

Metals are lustrous in appearance,. solid at room temperature (with the exception of mercury), good conductors of heat and electricity, malleable (can be hammered flat), and ductile (can be drawn into wires). Rgure 23.12 shows the positiotrs of the representative metals and the Group 

The metallic properties increase down any column and towards the left in any row on the periodic table. One important metallic property is that metal oxides are base anhydrides. A base anhydride will produce a base in water. These are not oxidation-reduction reactions. Many metal oxides are too insoluble for them to produce any significant amount of base. However, most metal oxides, even those that are not soluble in water, will behave as bases to acids. A few metal oxides, and their hydroxides, are amphoteric. Amphoteric means they may behave either as a base or as an acid. Amphoterism is important for aluminum, beryllium, and zinc. Complications occur whenever the oxidation number of the metal exceeds +4 as in the oxides that tend to be acidic. 

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We briefly examine the periodic trends in metallic properties. (20.4)... 

FIGURE 19.2 Periodic trends in the properties of the main-group elements. The metallic elements (green) and the nonmetallic elements (lavender) are separated by the heavy stairstep line. The semimetals, shown in blue, lie along the line. 

Describe some important periodic trends in the properties of Group IIIA metals and some of their compounds... 

Write electron configurations of transition metal atoms and ions compare periodic trends in atomic properties of transition elements with those of main-group elements explain why transition elements have multiple oxidation states, how their metallic behavior (type of bonding and oxide acidity) changes with oxidation state, and why many of their compounds are colored and paramagnetic ( 22.1) (SP 22.1) (EPS 22.1 -22.17)... 

The metals of interest and use in catalysis are confined to a very small area of the Periodic Table, so that most of our attention will be given to the nine metals in Groups 8 to 10, with only occasional mention of neighbouring elements in Groups 7 and 11, and of the earlier metals of the Transition Series (Figure 1.1). A principal object of our enquiry will be to understand why catalysis is thus restricted and our gaze will therefore be limited largely to the trends in metallic properties that occur in and immediately after the three Transition Series. 

Periodic trends in ionization energy are linked to trends involving the reactivity of metals. In general, the chemical reactivity of metals increases down a group and decreases across a period. These trends, as well as a further trend from metallic to non-metallic properties across a period, and increasing metallic properties down a group, are shown in Table 3.1. 

The oxides of main-group elements show periodic trends in properties. Oxides of metals tend to be ionic and to form basic solutions in water. Oxides of nonmetals are molecular and the anhydrides of acids. 

Alkali Metals Organometallic Chemistry Periodic Table Trends in the Properties of the Elements Zeolites. 

Electronic Structure of Solids Fluorides Solid-state Chemistry Halides Solid-state Chemistry Macrocyclic Ligands Metallic Materials Deposition Metal-organic Precursors Oxides Solid-state Chemistry Periodic Table Trends in the Properties of the Elements Sol-Gel Synthesis of Solids Sohds Characterization by Powder Diffraction Structure Property Maps for Inorganic Solids Superconductivity Thin Film Synthesis of Solids. 

Niobium (formerly called columbium) and tantalum are Transition Metals having a considerable affinity for oxygen donor groups they are thus called oxophilic see Oxophilic Character). They occur as mixed-metal oxides such as columbites (Fe/Mn)(Nb/Ta)206 and pyrochlore NaCaNb206p. Their discovery in minerals extends back to the beginning of the nineteenth century, when they were believed to be identical and called tantalum. Rose showed that at least two different elements were involved in the minerals, and named the second one niobium. Their separation was resolved around 1866, especially by Marignac. These metals often display similar chemical behavior as a result of nearly identical atomic radii (1.47 A) due to the lanthanide contraction see Periodic Table Trends in the Properties of the Elements)... 

Platinum (Z = 78) is a whitish, noble metal found in group 10 (or VIIIB) of the periodic table, in the triad with and lying below nickel and palladium (see Periodic Table Trends in the Properties of the Elements). It can be found in elemental form in the mountains of Columbia, where the pre-Columbian natives used it. European chemists discovered and reported it in the mid-1700s. Like gold and silver, it has a positive reduction potential ... 

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