1.5 Polar Covalent Bonds and Electronegativity 1.5 POLAR COVALENT BONDS AND ELECTRONEGATIVITY Electrons in covalent bonds are not necessarily shared equally by the two atoms that they connect. If one atom has a greater tendency to attract electrons toward itself than the other we say the electron distribution is polarized, and the bond is referred to as a polar cova lent bond. Hydrogen fluoride, for example, has a polar covalent bond. Because fluorine attracts electrons more strongly than hydrogen, the electrons in the H-F bond are pulled toward fluorine, giving it a partial negative charge, and away from hydrogen giving it a partial positive charge. This polarization of electron density is represented in various ways 6H—F6- H一F CThe symbols and (The symbol +represents indicate partial positive the direction of polarization and partial negativ of electrons in the h-F bond) y of an atom to draw the electrons in a covalent bond toward itself is referred to electronegativity. An electronegative element attracts electrons: an electropositive one donates them. Electronegativity increases across a row in the peri- odic table. The most electronegative of the second-row elements is fluorine; the most electropositive is lithium Electronegativity decreases in going down a column. Fluorine is more electronegative than chlorine. The most commonly cited electronegativity scale was devised by Linus Pauling and is presented in Table 1. 2. PROBLEM 1.8 Examples of carbon-containing compounds include methane( CHa) chloromethane(CHaCi), and methyllithium(CH3 Li). In which one does carbon bear the greatest partial positive charge? The greatest partial negative charge? Technology, where he Centers of positive and negative charge that are separated from each other consti- in 1925. In addition to re tute a dipole. The dipole moment u of a molecule is equal to the charge e(either the pauling studied the structure between the centers of charge: the Nobel Prize in chemistry for that work in 1954. Paul efforts to limit the testing of uclear weapons. He was TABLE 1.2 Selected Values from the Pauling Electronegativity Scale ive won two Nobel prizes a woman. Can you name Group number Period H2u B C N 3.0 18 0.8 1.0 2.8 2.5 Back Forward Main MenuToc Study Guide ToC Student o MHHE Website1.5 POLAR COVALENT BONDS AND ELECTRONEGATIVITY Electrons in covalent bonds are not necessarily shared equally by the two atoms that they connect. If one atom has a greater tendency to attract electrons toward itself than the other, we say the electron distribution is polarized, and the bond is referred to as a polar cova￾lent bond. Hydrogen fluoride, for example, has a polar covalent bond. Because fluorine attracts electrons more strongly than hydrogen, the electrons in the H±F bond are pulled toward fluorine, giving it a partial negative charge, and away from hydrogen giving it a partial positive charge. This polarization of electron density is represented in various ways. The tendency of an atom to draw the electrons in a covalent bond toward itself is referred to as its electronegativity. An electronegative element attracts electrons; an electropositive one donates them. Electronegativity increases across a row in the peri￾odic table. The most electronegative of the second-row elements is fluorine; the most electropositive is lithium. Electronegativity decreases in going down a column. Fluorine is more electronegative than chlorine. The most commonly cited electronegativity scale was devised by Linus Pauling and is presented in Table 1.2. PROBLEM 1.8 Examples of carbon-containing compounds include methane (CH4), chloromethane (CH3Cl), and methyllithium (CH3Li). In which one does carbon bear the greatest partial positive charge? The greatest partial negative charge? Centers of positive and negative charge that are separated from each other consti￾tute a dipole. The dipole moment of a molecule is equal to the charge e (either the positive or the negative charge, since they must be equal) multiplied by the distance between the centers of charge:  e  d (The symbols  and  indicate partial positive and partial negative charge, respectively) H±F  H±F (The symbol represents the direction of polarization of electrons in the H±F bond) 1.5 Polar Covalent Bonds and Electronegativity 15 TABLE 1.2 Selected Values from the Pauling Electronegativity Scale Group number Period 1 2 3 4 5 I H 2.1 Li 1.0 Na 0.9 K 0.8 II Be 1.5 Mg 1.2 Ca 1.0 III B 2.0 Al 1.5 IV C 2.5 Si 1.8 V N 3.0 P 2.1 VI O 3.5 S 2.5 VII F 4.0 Cl 3.0 Br 2.8 I 2.5 Linus Pauling (1901–1994) was born in Portland, Ore￾gon and was educated at Oregon State University and at the California Institute of Technology, where he earned a Ph.D. in chemistry in 1925. In addition to re￾search in bonding theory, Pauling studied the structure of proteins and was awarded the Nobel Prize in chemistry for that work in 1954. Paul￾ing won a second Nobel Prize (the Peace Prize) for his efforts to limit the testing of nuclear weapons. He was one of only four scientists to have won two Nobel Prizes. The first double winner was a woman. Can you name her? Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website