Periodic trends representative elements

New scientific methods (e.g. electrolysis) allowed the veteran elements to be joined stepwise by more and more unknown and unexpected substances that fulfilled the criteria for an element. In 1869, after many attempts to bring order into the growing chaos, Dimitri Mendeleev revealed a daring concept with his Periodic Table and its predictions. Each of the then known elements was assigned a place. The gaps represented elements that were not yet known. The discoveries of such elements proved that there was an order and system to the elements. This order explained much that was previously puzzling, for instance, the different atomic radii observed that same year by Julius Lothar Meyer, which seemed to follow a periodic trend. 

What do elements look like How do they behave Can periodic trends in the properties of elements be observed You cannot examine all of the elements on the periodic table because of limited availability, cost, and safety concerns. However, you can observe several of the representative elements, classify them, and compare their properties. The observation of the properties of elements is called descriptive chemistry. 

Recall that metals tend to lose electrons. Thus, the lower the ionization energy, the more reactive the metal. For a group of metals, reachvity increases as the atomic number increases. The opposite is true for nonmetals because nonmetals tend to gain electrons. The higher the ionization energy of a non-metal, the more reactive the nonmetal. For a group of nonmetals, reactivity decreases as the atomic number increases. Of the representative elements, which is the most reactive metal Which is the most reactive nonmetal (Hint What is the trend for ionization energy across a period )... 

FIGURE 8.5 Atomic radii (in picometersj of representative elements according to their positions in the periodic table. Note that there is no general agreement on the size of atomic radii. We focus only on the trends in atomic radii, not on their precise values. 

Make and Use Graphs Graph the atomic radii of the representative elements in periods 2,3, and 4 versus their atomic numbers. Connect the points of elements in each period, so that there are three separate curves on the graph. Summarize the trends in atomic radii shown on your graph. Explain. 

Overall, the computed and represented atomic scales for the reactivity indices x, fj, IP, and EA of this venture display a systematic qualitative periodic trend across the ordinary elements being in a relatively quantitative acceptable ratio with the experimental values, where these are available. 

Our two periodic trends in atomic size do not supply enough information to allow us to determine, however, whether B or Si (represented by the two question marks) has the larger radius. Going from B to Si in the periodic table, we move down (radius tends to increase) and to the right (radius tends to decrease). It is only because Figure 7.7 provides numerical values for each atomic radius that we know that the radius of Si is greater than that of B. If you examine the figure carefully, you will discover that for the s- andp-block elements the increase... 

Figure 2.12 I The data from Figure 2.11 are presented here in a different form. The shading of the boxes in the periodic table represents the density of each element darker shading indicates higher density. The general trends in density are apparent as you look across a row or down a column.

The periodic trends in the first ionization energies of the representative elements are further illustrated in Figure 7.10 T. 

Trends in properties occur in elements that form periods across the periodic table as well as among those that form vertical groups. We will discuss two of these properties and their trends for representative elements. Our focus will be on the general trends, recognizing that some elements show deviations from these general behaviors. We will also propose explanations for the trends based on the electronic structure of atoms discussed in the chapter. 

Experimentally, electron affinity is determined by removing the additional electron from an anion. In contrast to ionization energies, however, electron affinities are difficult to measme because the anions of many elements are unstable. Table 8.3 shows the electron affinities of some representative elements and the noble gases. The overall trend is an increase in the tendency to accept electrons (electron affinity values become more positive) from left to right across a period. The electron affinities of metals are generally lower than those of nonmetals. The values vary little within a given group. The... 

TABLE 5.5 Summary of Trends in Periodic Properties of Representative Elements... 

Another chapter (Chapter 4) is entitled Intermetallic reactivity trends in the Periodic Table . The Periodic Table, indeed (or Periodic Law or Periodic System of Chemical Elements), is acknowledged to play an indispensable role in several different sciences. Especially in inorganic chemistry it represents a fundamental classifi-catory scheme and a means of systematizing data with a clear predictive power. Inorganic chemists have traditionally made considerable use of the Periodic Table to understand the chemistry of the different elements. With a few exceptions (as detailed in the same chapter), metallurgists and intermetallic chemists have made little use of this Table to understand and describe the properties of metals and alloys we believe, however, that it may be a useful tool also in the systematics of descriptive intermetallic chemistry (as exemplified in the subsequent chapter (Chapter 5)). In several paragraphs of Chapter 4, therefore, different aspects of the Periodic Table and of its characteristic trends are summarized. 

As already suggested and discussed by several authors, such as Pettifor (1984, 1986), Villars etal. (1989), etc., these maps highlight a regular trend in the formation of binary compounds. In the lower-left corner of the map those systems are represented obtained by combinations among elements of the first four groups of the Periodic Table. 

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