Tables, electronegativity

Use the electronegativity table (figure 2.2) to predict which bond in each of the following sets is more polar, and indicate the direction of bond polarity for each compound. 

Use an electronegativity table (see page 169 in your textbook) to determine the electronegativity difference between the two elements in the compounds in Data Table 2. 

Electronegativity. Table 4.2 makes it apparent that atoms differ in their relative power of attraction for a shared electron pair, i.e., they have different electronegativities. One might ask which factors can explain the relative electron attracting power of atoms in covalent bonds. 

Some intermetallic compounds have the same structures as those of simple polar compounds. Quite a few AM type intermetallic compounds have the NaCl (3 2PO, Section 5.1.1) structure, but usually for those differing significantly in electronegativities. Table 5.1 includes many compounds of the types MP, MAs, MSb, and MBi. The NiAs structure (2-2PO, Section 5.2.1) is found for a few MAs and MSb compounds (Table 5.5), the MSn compounds of Fe, Ni, Cu, Pd, Pt, Rh, and Au, and MnBi, NiBi, PtBi, and RhBi. The ZnS structures (CN 4) are not usually encountered for intermetallic compounds. The compounds of Al, Ga, and In with P, As, and Sb have the zinc blende (ZnS, 3 2PT, Section 6.1.1) structure. These are semiconductors or insulators. Because the bcc structure is common for metals, it is not surprising that many 1 1 intermetallic compounds have the CsCl structure (3 2PTOT, Section 7.2.1). A few of these intermetallic compounds are included in Table 7.1 a more extensive list is given in Table 9.1. 

Some AM2 type structures have the fluorite structure, but for metals differing significantly in electronegativities. Table 6.4 contains many intermetallic compounds with the fluorite structure. Table 9.2 contains... 

Because the strength of the C=0 bond correlates with its stretching frequency, the latter increases when the substituent X becomes more electronegative (Table 2.2). Complete abstraction of the group X (e.g. for X = BF4 ) leads to the formation of acylium cations with a short and strong C=0 bond, as revealed by the high vibrational IR-frequency of these compounds [24] (Table 2.2). 

With more than 100 elements besides carbon in the periodic table (Appendix 2), you might fear that the number of H chemical shift correlations is endless. However, except for a few specialized applications, the most important heteroatoms to which hydrogen finds itself bonded are oxygen and nitrogen. But before we discuss these two specific cases, here is a useful generalization As the electronegativity (Table 6.1) of X increases, both the acidity and chemical shift of a hydrogen bonded directly to X increase. 

Fortunately, chemists do not have to memorize which compounds do or do not have ionic bonds. A simple rule of thumb helps them to gauge the type of bond that forms between two atoms. All one needs is an electronegativity table, such as Table 3.2 in the previous chapter. Experience has shown that when the difference in electronegativity of two atoms is equal to or greater... 

With an electronegativity table, establishing the ionic or covalent nature of the bond between two atoms is just a matter of simple subtraction. However, there is more to understanding the chemical bond than just knowing the electronegativity of atoms. Several other bond variations will be covered in the next chapter. 

We should remark that of the compounds listed in Table 4-1, BP and BAs have negative metallic atoms (Z < 0), and BeO is near zero. Similarly, the electronegativity tables of Pauling or of Phillips (these can be compared in Phillips, 1973a, p. 54) suggest that Be and B may be negative in some compounds. 

Silylphosphines, (R3Si)3P, are well known. On the basis of electronegativity (Table 1) they are weaker n acids than organophosphines. With the isolation of R2Si=PR compounds, an increased variety of structmes is available. Six-membered silicon-phosphorus heterocycles (1) have been proposed as ligands for catalyst candidates, owing to the steric accessibility of the transition metal. 

Electronegativity values have been derived in a number of ways. The first of these was by Pauling and made use of thermochemical data to obtain a scale of relative values for elements. Most electronegativity tables since then have also contained relative values, which do not have units. 

One source of such ions is a reaction between atoms of widely differing electronegativities (Table 1.1). 

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