Electronegativity

Electronegativity, symbol χ, is a chemical property that describes the tendency of an atom or a functional group to attract electrons (or electron density) towards itself.

Quotes

 * Bond polarity is due to differences in electronegativity (EN), the intrinsic ability of an atom to attract the shared electrons in a covalent bond. As shown in Figure 2.2, electronegativities are based on an arbitrary scale, with fluorine the most electronegative (EN =4.0) and cesium the least (EN =0.7). Metals on the left side of the periodic table attract electrons weakly and have lower electronegativities, while oxygen, nitrogen, and halogens on the right side of the periodic table attract electrons strongly and have higher electronegativities. Carbon, the most important element in organic compounds, has an electronegativity value of 2.5.… As a rough guide, bonds between atoms whose electronegativities differ by less than 0.5 are nonpolar covalent, bonds between atoms whose electronegativities differ by 0.5–2 are polar covalent, and bonds between atoms whose electronegativities differ by more than 2 are largely ionic.
 * John McMurry, Organic Chemistry 8th ed. (2012), Ch. 2 : Polar Covalent Bonds; Acids and Bases