Periodic trends in atomic radii

Within each group, bonding atomic radius tends to increase from top to bottom. This trend results primarily from the increase in the principal quantum number (n) of the outer electrons. As we go down a column, the outer electrons have a greater probability of being farther from the nucleus, causing the atomic radius to increase. 

In Section 7.2 we said that Zgff generally increases when you move down a column of the periodic table, whereas in Chapter 6 we saw that the size of an orbital increases as the principal quantum number n increases. With respect to atomic radii, do these trends work together or against each other Which effect is larger  

Referring to a periodic table, arrange (as much as possible) the atoms 15P, [58,33As, and 34Se in order of increasing size. (Atomic numbers are given to help you locate the atoms quickly in the table.) 

Analyze and Plan We are given the chemical symbols for four elements and told to use their relative positions in the periodic table to predict the relative size of their atomic radii. We can use the two periodic trends just described to help with this problem. 

Solve P and S are in the same period, with S to the right of P. Therefore, we expect the radius of S to be smaller than that of P because radii decrease as we move across a period. Likewise, the radius of Se is expected to be smaller than that of As. As is directly below P, and Se is directly below S. We expect, therefore, the radius of P to be smaller than that of As and the radius of S to be smaller than that of Se. Thus, so far we can say S P,P As,S Se,Se As. We can therefore conclude that S has the smallest radius and As has the largest radius and so can write S As. 

EXERCISE 7.2 Predicting Relative Sizes of Atomic Radii 

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Account for periodic trends in atomic radii, ionization energies, and electron affinities (Examples 1.11 and 1.12). 

The nine d-block elements of period 6 viz. Hf to Hg have [Xe]4/l4 core like lutetium and not just the [Xe] core of the lanthanum. Similarly, in passing down the columns of the d-block from Ti to Zn, the addition of 4/ subshell is encountered in moving from period 5 to 6. The periodic trends in atomic radii, sum of the first two ionization potentials, melting... 

Answer the following questions using your knowledge of group and period trends in atomic radii. Do not use the atomic radii values in Figure 6-11 to answer the questions. 

The period trend in atomic radii has been correctly applied. Checking radii values in Figure 6.10 verifies the answer. ... 

Knowledge Required (1) The periodic trends in atomic radii within groups and periods. 

Strategy Use the periodic trends in atomic radii—namely, atomic radius decreases from left to right across a period and increases from top to bottom down a group. 

Relate period and group trends in atomic radii to electron configuration. 

You are given four elements. First, determine the groups and periods the elements occupy. Then apply the general trends in atomic radii to determine which has the largest atomic radius. 

B radii of the group A 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. 

General trends in atomic radii of A group elements with position in the periodic table. 

T1.5 The variation of atomic radii is one of the periodic trends, and as such could be used to group the elements. Look up the atomic radii of the six elements and see which grouping, (a) or (b), better follows the expected trends in atomic radii. After that you should extend your discussion to the chemical properties of the elements in question and see if your choice makes chemical sense as well. 

We are more interested in the trends in atomic radii within groups and periods as opposed to the actual numbers. The trends in atomic radii are easily seen in the following figure. 

What are the general trends in atomic radii on the periodic table ... 

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. 

Strategy What are the trends in atomic radii in a periodic group and in a particular period. Which of the above elements are in the same group and which are in the same period ... 

Use the periodic table to predict the trends in atomic radii, ionic radii, ionization energy, and electron affinity. (Sections 7.2,7.3,7.4, and 7.5)... 

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