Polarity Trends in Bonds

Let us look at the polarity of H—X bonds, where X is an atom in a given family. To do so, we must use the EN values of the atoms, which can be taken from the EN table in 

SCHEME 7.11 Electronegativity (EN) trends in the periodic table. The arrows indicate the directions in which EN increases in a period and in a family. 

TABLE 7.1 H—X Bonds (X Varies down a Colnmn), the Electronegativity (EN) of Their Constituents, and EN Differences 

It is seen that for all the bonds, X is more electronegative than H and hence the bonds are polarized in the sense of H(6+) and X(6 ). However, as X changes down the column from F to I, the EN of X decreases and the EN difference also decreases, such that the partial charges get smaller as we go down the period from H—F to H—I. 

The same trends as in the above tables are expected for any bond type when varying one atom along a family and a period. 

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