Periodic table electron affinity trends

Figure 8.1 S Trends in three atomic properties. Periodic trends are depicted as gradations in shading on miniature periodic tables, with arrows indicating the direction of general increase in a group or period. For electron affinity. Group 8A0 8) is not shown, and the dashed arrows indicate the numerous exceptions to expected trends.

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... 

The groups and periods of the periodic table display general trends in the following properties of the elements electron affinity, electronegativity, ionization energy, atomic radius, and ionic radius. 

Nonmetals follow the general trends of atomic radii, ionization energy, and electron affinity. Radii increase to the left in any row and down any column on the periodic table. Ionization energies and electron affinities increase up any column and towards the right in any row on the periodic table. The noble gases do not have electron affinity values. Ionization energies are not very important for the nonmetals because they normally form anions. Variations appear whenever the nonmetal has a half-filled or filled subshell of electrons. The electronegativity... 

Sketch an outline of the periodic table and use it to compare the trends in atomic size, first ionization energy, and electron affinity. 

Figure 1.2 Some important trends in the periodic table for (a) ionization energy, (b) electron affinity, (c) atomic and ionic radii, and (d) electronegativity. Increasing values are in the direction of the arrow.

Increasing numbers of protons increase the positive charge of the nucleus, which contributes to electron affinity, the attraction an atom has for an added electron. Electron affinity increases as move you up and to the right on the periodic table. Within a period, the more protons an element has, the stronger its electron affinity tends to be. This trend isn t perfectly smooth because other, more subtle factors cire at work, but it s a good general... 

The most obvious chemical significance of the electronic structure of atoms lies in the factors that determine ionization energies, electron affinities, and the sizes of atoms. This section looks briefly at some of the trends— vertically and horizontally in the periodic table—in such properties. 

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. 

We have developed a fairly complete picture of polyelectronic atoms that is quite successful in accounting for the periodic table of elements. We will next use the model to account for the observed trends in several important atomic properties ionization energy, electron affinity, and atomic size. 

Describe the trends in electron affinity and electronegativity across the periodic table (Section 3.4, Problems 13-16). 

Describe the trends in ionization energy and electron affinity across the periodic table and relate them to the electronic structure of atoms (Section 5.5, Problems 35-40). 

The electron affinities of the main group homonuclear diatomic anions have been measured by PES. A few experimental values for the transition metal dimers are also available. The electron affinities of all the 3d homonuclear diatomic molecules have been calculated using density functional methods [1-4], Only the AEa of I2, 2.524 eV C2, 3.27 Si2, 2.2o S2, 1.67 F2, 3.0g Cl2, 2.4s Br2, 2.5, and 02, 1.07 have been measured by more than one method [1-3]. CURES-EC calculations confirm these to within 0.1 eV. Positive excited states Ea have been measured for 02, C2, and I2 and are inferred for other X2 [5-8]. Just as in the case of the atomic Ea, the trends in the Periodic Table can support the assignments of AEa for the other elements. 

General trends in electron affinities of A group elements with position in the periodic table. There are many exceptions. 

Remember ionization energy and electron affinity (below) are predictable from trends in the periodic table. As with most trends, exceptions occur. 

Three atomic properties—atomic size, ionization energy (energy involved in removing an electron from an atom), and electron affinity (energy involved in adding an electron to an atom)—exhibit recurring trends throughout the periodic table. 

---