Atomic Radii of the Elements

FIGURE 1.47 The periodic variation in the atomic radii of the elements. The variation across a period can be explained in terms of the effect of increasing effective nuclear charge that down a group by the occupation of shells with inc reasing principal quantum number. 

Explain the decrease in atomic radii of the elements in period 3. 

A) Alkali metals have one electron in their outer shell, which is loosely bound. This gives them the largest atomic radii of the elements in their respective periods. Their low ionization energies result in their metallic properties and high reactivities. An alkali metal can easily lose its valence electron to form the univalent cation. Alkali metals have low electronegativities. They react readily with nonmetals, particularly halogens. 

If both the melting points and the atomic radii of the elements are close, two compound layers may well be expected to grow at comparable rates. The melting point of molybdenum is 2620°C, while that of iridium is... 

Refer to Appendix A for a chart of relative atomic radii of the elements. 

Table 3.1 The variation of atomic radii of the elements, (a) the alkali metals, (b) the halogens and (c) the second short period...

Describe how the atomic radii of the elements in Group 2 change as you move down the group. Give reasons for this trend. 

The nearly identical atomic radii of the iron triad—iron, cobalt, and nickel —help explain the similar chemistry of these three elements. The similarities among the platinum group elements in Periods 5 and 6 emphasize the fact that there is little difference between the atomic radii of the elements in these periods in which inner d orbitals are being filled. The coinage metals show the expected similarity among elements in the same group. 

The van der Waals volume can be estimated by assuming that the impenetrable volume of a molecule is bounded by the outer surface of a number of interpenetrating spheres [1J. The radii of the spheres are assumed to be the constant (standard) atomic radii of the elements involved. The distances between the centers of the spheres are assumed to be the constant (standard) bond lengths for each type of bond involved. The contribution of each atom to Vw can then be... 

II) Why do the atomic radii of the elements increase as the groups are descended ... 

Selecting Atomic Radii of the Elements Selecting Ionic Radii of the Elements Bond Lengths and Angles... 

The values of the atomic radii of the elements in Period 3 are given in Table 10.1. We can see the pattern across the period more clearly on a graph (Figure 10.4). 

Atomic mass unit (amu), 1-1 to 11,1-23 to 26 Atomic masses, 1-14 to 17,11-56 to 253 Atomic Masses and Abundances, 1-14 to 17 Atomic Radii of the Elements, 9-49 Atomic radius, rare earth elements, 4-127 to 132... 

In general, atomic radii increase while going down the group. Therefore, the atomic radii of the elements of second transition series have hi er values than those of the elements of first transition series. This is due to increase in the number of electron shells. The atomic radii of the elements of third transition series except lanthanum have almost the same atomic radii as the elements of second transition series. This is due to lanthanide contraction. The fourteen lanthanides are present between lanthanum and hafiiium (syLa - 72HiD and there is a continuous decrease in atomic size from cerium (sgCe) to luteciiun (yiLu) so that the atomic size of hafnium becomes almost equal to the size of zirconium. 

The atomic radii of the elements of third transition (5d) series are slightly greater than those of first transition (3d) series but atomic numbers differs by 50. Thus, in the 5d series the outer electrons are firmly attached to the nucleus and ionization energies are very high. 

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