Periodic Table, electronegativity trends

Figure 2.2 Electronegativity values and trends. Electronegativity generally increases from left to right across the periodic table and decreases front top to bottom. The values are on an arbitrary scale, with F = 4.0 and Cs = 0.7. Elements in orange are the most electronegative, those in yellow are medium, and those in green are the least electronegative.

The larger the difference in electronegativity, the more polar the bond. Therefore, we can use periodic trends in electronegativities to arrange these bonds in order of polarity. Electronegativities decrease down most columns and increase from left to right across the s and p blocks. Use the periodic table to compare electronegativity values and rank the bond polarities. 

The first task is to decide whether the members of a given group are Lewis acids or bases. Then evaluate the relative softness and hardness based on polarizability, taking into account correlations with electronegativity, size, and charge. Refer to the periodic table in assessing the trends. 

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... 

The same trends are expected to be found when the atom X is varied along another column of the Periodic Table, i.e. decreasing electronegativity of X along a column should lead to lower ctcx energy. Thus, for example, in the reductive C—X bond cleavage of PhCOCRR XPh, the half wave reduction potential is less for X=S than X=042). Relevant computational results are shown in Table 4. 

The Ox h energy of an X—H bond decreases with replacement of a first period atom by a second period atom. This trend is shown in Table 5. The energy of ox h also decreases as the electronegativity of X increases along a row of the Periodic Table. 

On the basis of the Periodic Table, topics of intermetallic systematics will be presented in the next chapter. In the present chapter the Periodic Table will be revisited and its structure and subdivisions summarized. In relation also to some concepts previously presented, such as electronegativity, Mendeleev number, etc. described in Chapter 2, typical property trends along the Table will be shown. Strictly related concepts, such as Periodic Table group number, average group number and valence-electron number will be considered and used in the description and classification of intermetallic phase families. 

Identify trends in the periodic table for IE, EA, electronegativity, and atomic/ionic radii. 

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.

True, except for the group 18 noble gas elements, which are not assigned an electronegativity number. The trend is that electronegativity decreases with an increasing number of shells down any one atomic group (vertical column) of the periodic table. 

Similar trends can also be observed for X = AIH149, SiH232b-47-, 24, PH47-124 and S47-124 where, however, CC bond shortening and the increase in y are somewhat smaller because of the decrease in electronegativity when going up in the columns of the periodic table. 

FIGURE 7.4 Electronegativity trends in the periodic table. Electronegativity increases from left to right and generally decreases from top to bottom. 

What general trends in electronegativity occur in the periodic table ... 

Use the Interactive Periodic Table (eChapter 7.4) to determine the trend in electronegativity as you move across a row in the periodic table. What element would you expect to have the largest electronegativity What factors contribute to the trends in electronegativity ... 

The group 4A elements exemplify the increase in metallic character down a group in the periodic table Carbon is a nonmetal silicon and germanium are semimetals and tin and lead are metals. The usual periodic trends in atomic size, ionization energy, and electronegativity are evident in the data of Table 19.4. 

In addition to the information below, the periodic table shows trends in atomic size, ionization energy, electronegativity, valence electrons, and melting points. 

The same is true for anions where the nucleophilic centre is an element in the same row of the periodic table (e.g., C, N, O, F). Thus, the order of nucleophilicity of the following anions (R )C > R2N > RO > F ) is the same as their order of basicity. This trend can be related to the electronegativities of these atoms. The more electronegative the atom (e.g., F), the more tightly it holds on to its electrons and the less available these electrons are for forming new bonds (less nucleophilic). 

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. 

---