Increases down a group

Figure 1.46 shows some atomic radii, and Fig. 1.47 shows the variation in atomic radius with atomic number. Note the periodic, sawtooth pattern in the latter plot. Atomic radius generally decreases from left to right across a period and increases down a group. 

Ionic radii generally increase down a group and decrease from left to right across a period. Cations are smaller than their parent atoms and anions are larger. 

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). 

FIGURE 14.5 The polarizability of atoms tends to decrease from left to right jeross a period and to increase down a group. 

L (a) Size increases down a group and from right to left in a period. Ba is closest to the... 

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. 

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. 

Bismuth is the least toxic of the As, Sb, Bi triad, which is unusual, since toxicity normally increases down a group, as shown by elements to the left of bismuth, i.e. Pb, Tl, Hg. However, it must be emphasized that this is not to say that bismuth is not toxic and experimentalists should avoid contact and ingestion of its compounds. 

FIGURE 1.35 The atomic radii (in picometers, 1 pm = 10 12 m) of the main-group elements. The radii decrease from left to right in a period and increase down a group. The colors used here and in subsequent charts represent the general magnitude of the property, as indicated by the scale on the right. Atomic radii are listed in Appendix 2D. 

The increase down a group, like that from Li to Cs, makes sense with each new period, the outermost electrons occupy shells that lie farther from the nucleus. But the decrease across a period, like that from Li to Ne, is surprising at first, because the number of electrons is increasing along with the number of protons. The explanation is that the new electrons are in the same shell of the atom and about as close to the nucleus as other electrons in the same shell. Because they are spread out, they do not shield one another well from the nuclear charge, so the effective nuclear charge increases across the period. The increasing effective... 

Atomic radii generally increase down a group and decrease across a... 

Covalent radii typically decrease from left to right across a period. The reason is the same as for atomic radii (Section 1.15) the increasing effective nuclear charge draws in the electrons and makes the atom more compact. Like atomic radii, covalent radii increase down a group because, in successive periods, the valence electrons occupy shells that are more distant from the nucleus and are better shielded by the inner core of electrons. Such fatter atoms cannot approach their neighbors very closely hence they form long, weak bonds. 

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. 

Atomic radius decreases across a period and increases down a group. 

Atomic radius increases down a group, because of the increases in the orbital sizes in successive principal quantum levels. 

We expect the atomic radius to increase down a group in the periodic table. Can you suggest why the atomic radius of hafnium breaks this rule (See the following data.)... 

Sizes of ions related to positions of elements in the periodic table. Note that size generally increases down a group. Also note that in a series of isoelectronic ions, size decreases with increasing atomic number. The ionic radii are given in units of picometers. 

The resulting bond-energy data [27] are siunmarized in Table 2. As in Table 1, there is an unambiguous trend that BDEs increase down a group in the periodic table. Ligand effects are less clear-cut and will be discussed in Section 3.3.4. 

Heats of formation of the oxides usually increase down a group in the Periodic Table ... 

Atomic radius generally increases down a group and decreases across a period, as shown in this diagram. Darker shading indicates higher atomic radius. 

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