Metallic character, periodic trends

The final important periodic trend, metallic character, tends to increase from right to left and top to bottom. 

T nGURE8.18 Trends in Metallic Character II As we move down group 5 A in the periodic table, metallic character increases. As we move across period 3, metaUic character decreases. 

The group 4A elements exemplify the increase in metallic character down a group in the periodic table Carbon is a nonmetal silicon and germanium are semimetals and tin and lead are metals. The usual periodic trends in atomic size, ionization energy, and electronegativity are evident in the data of Table 19.4. 

The group 6A elements are oxygen, sulfur, selenium, tellurium, and polonium. As shown in Table 19.7, their properties exhibit the usual periodic trends. Both oxygen and sulfur are typical nonmetals. Selenium and tellurium are primarily non-metallic in character, though the most stable allotrope of selenium, gray selenium, is a lustrous semiconducting solid. Tellurium is also a semiconductor and is usually classified as a semimetal. Polonium, a radioactive element that occurs in trace amounts in uranium ores, is a silvery white metal. 

To compare the size of an atom, we need to compare radii among different atoms using some standard. As seen to the right, the sizes of atoms decrease with period number and increase with group number. This trend is similar to the trend described above for metallic character. The smallest atom is helium. 

It has already been emphasized that within a family of non transition elements, metallic character increases with increase in atomic number, atomic weight, and atomic size. There is no better illustration of this trend than Periodic Group Vb the lightest members of the group, nitrogen (Z = 7), and phosphorus (Z — 15), are typical nonmetals, whereas the heaviest member, bismuth (Z = 83) is a typical metal. The remaining members, arsenic (Z = 33) and antimony (Z 51) are intermediate in character and are often appropriately called metalloids. 

The metallic character of the elements in the periodic table, and the acid-base properties of their oxides, show a distinct trend across periods and down groups. Infer what this trend is. 

The oxides of the Group 15 elements clearly exemplify two important trends that are manifest to some extent in all main groups of the Periodic Table (1) the stability of the higher oxidation state decreases with increasing atomic number, and (2) in a given oxidation state the metallic character of the elements, therefore the basicity of the oxides, increases with increasing atomic number. Thus Pm and Asra oxides are acidic, Sb111 oxide is amphoteric, and Bim oxide is strictly basic. 

The members of group of the periodic table show the expected trend in properties with increasing atomic number (f able 21 1) nitrogen is a gas which can be condensed to a liquid only at very low temperatures phosphorus (in the modification called w I tilt phosphorus) is a low-melting non-metal and arsenic, antimony, and bismuth are metalloids with increasing metallic character. 

General trends in metallic character of A group elements with position in the periodic table. 

Another group trend with />block elements is the increasing tendency towards metallic character in lower periods. As with the chemical trends, the change in structures and properties of the elements appears more of a continuous transition than a sharp borderline (see Topics B2 and D7). The structural distinction between near-neighbor (bonded) atoms and next-near-neighbor (nonbonded) ones... 

We have seen that the metallic character of the elements decreases from left to right across a period and increases from top to bottom within a group. On the basis of these trends and the knowledge that metals usually have low ionization energies while nonmetals usually have high electron affinities, we can frequently predict the outcome of a reaction involving some of these elements. 

Summarize the trend in metallic character as a function of position in the periodic table. Is it the same as the trend in atomic size Ionization energy ... 

Metal oxides are ionic and act as bases in water nonmetal oxides are covalent and act as acids in water. 8.48 Metallic character increases down a group and decreases toward the right across a period. These trends are the same as those foratomic size and opposite those for ionization energy. 8.52(a) Rb (b) Ra (c) 1... 

The trends in metallic and non-metallic character of the elements within groups and periods within the periodic table may be summarized in the following diagram ... 

How are metallic character and first ionization energy related [7.58] It is possible to define metallic character as we do in this book and base it on the reactivity of the element and the ease with which it loses electrons. Alternatively, one could measure how well electricity is conducted by each of the elements to determine how metallic the elements are. On the basis of conductivity, there is not much of a trend in the periodic table Silver is the most conductive metal, and manganese the least. Look up the first ionization energies of silver and manganese which of these two elements would you call more metaUic based on the way we define it in this book ... 

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