Atomic radius/radii periodic trends

Atomic radii typically decrease from left to right across a period and increase down a group (Fig. 14.2 see also Fig. 1.46). As the nuclear charge experienced by the valence electrons increases across a period, the electrons are pulled closer to the nucleus, so decreasing the atomic radius. Down a group the valence electrons are farther and farther from the nucleus, which increases the atomic radius. Ionic radii follow similar periodic trends (see Fig. 1.48). 

II. The general trend is for ionization energy to increase as one moves from left to right across the periodic table and to decrease as one moves down this is the inverse of the trend one finds in examining the atomic radius. 

Figure 3.23 shows the periodic trends associated with the atomic radius. You can see that atomic radii generally decrease across a period. Furthermore, atomic radii generally increase down a group. Two factors affect differences in atomic radii. 

Zeff governs the trend of decreasing atomic radius across a period. 

Ionization energy generally increases across a period. Again, this trend is linked to the atomic radius. Across a period, the atomic radius decreases because Zeff increases. The force of attraction between the nucleus and valence electrons is subsequently increased. Therefore, more energy is needed to remove one such electron. 

The periodic trend for electronegativity is the inverse of the trend for atomic radius. 

FIGURE 14.1 The general tendency of atomic radius is to decrease across a period and increase down a group. This diagram is a highly schematic representation of those trends. 

Use the Interactive Periodic Table in eChapter 5.15 to determine the trend in atomic radius as you move across a period and as you move down a group. Explain the factors that account for these trends. 

Use the Interactive Periodic Table (eChapter 5.1) to compare the atomic radius and the ionic radius of the elements in group 2A. How does the ionic radius compare to the atomic radius Explain this trend. 

A horizontal row is called a period. As one travels from left to right across a period certain trends occur. In general, atomic radius decreases from left to right (disregarding the noble gases). Metallic properties also decrease from left to right. 

Metallic and nonmetallic properties are related to the number of valence electrons and the radius of an atom. Within a period, as the metallic properties decrease from left to right, the nonmetallic properties increase. Within a group as the metallic properties increase, the nonmetallic properties decrease from top to bottom. If the above trends are considered, francium, Fr, would be expected to have most metallic properties. However, since Fr is a radioactive element, not all of its properties have been determined yet. 

Within a given group of the periodic table, the first ionization energy decreases with increasing atomic number. This is related to the increase in atomic radius and the decreasing attraction of the nucleus for the increasingly distant outermost electron. It should be mentioned that this trend is not uniformly noted for the transition metals. 

Because of the arrangement of elements on the periodic table, there are several patterns that can be seen between the elements. These patterns, or periodic trends, can be observed for atomic radius, ionic radii, ionization energies, electron affinities, and electronegativities. You should be familiar with the periodic and group trends for each of these. 

Your understanding of periodic trends such as atomic radius and ionization energy will help you identify some unknown elements in the Chemistry Course Challenge at the end of this book. 

Know the trends for electronegativity, ionization energy, and atomic radius across the periodic table. 

Extended structures of (at least) binary compounds EX most frequently involve covalent bonding between the simplest formula units EiX via E and X atoms or groups that are bridging (two-coordinate or higher), rather than terminal (one-coordinate). Moderately accurate predictions of periodic trends in structural types for EX can be made using stoichiometry and radius-ratio calculations (starting with the premise that the compound can be formed, at least conceptually, from cations of E and anions of X). (1) If the radius ratio of the ions in the compound EX lies between 0.225 and 0.414, E is predicted to have a total coordination number of 4 if the ratio lies between 0.414 and 0.732, E should have a total coordination number of 6 if the ratio is above 0.732, E should have a total coordination number of 8. (2) Once the coordination number of E is predicted, the average coordination number of the anionic element X can be predicted ... 

Does the information on alkali metals in Table 12.9 of the text confirm the general periodic trends in ionization energy and atomic radius Explain. 

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