6.7 Electronegativity and Bond Polarity The electronegativity values of representative elements in Group 1A (1) to Group 7A (17). Learning Goal Use electronegativity to determine the polarity of a bond.

Electronegativity The electronegativity of an atom is its ability to attract the shared electrons in a bond. It increases from left to right going across a period on the periodic table. increases from the bottom to the top of the periodic table. is high for the nonmetals, with fluorine as the highest. is low for the metals. Core Chemistry Skill Using Electronegativity

Electronegativity and the Periodic Table

Polarity of Bonds The difference in electronegativity of bonding atoms can be used to predict the polarity of the bond. In the H2 molecule, electrons are shared equally and the bond is nonpolar. In the HCl molecule, electrons are shared unequally, and the bond is polar.

Nonpolar Covalent Bonds A nonpolar covalent bond occurs between nonmetals. It is an equal or almost equal sharing of electrons by the two bonding atoms. has a very small electronegativity difference between atoms. Examples Electronegativity Atoms Difference Type of Bond N-N 3.0 − 3.0 = 0.0 Nonpolar covalent Cl-Br 3.0 − 2.8 = 0.2 Nonpolar covalent H-Si 2.1 − 1.8 = 0.3 Nonpolar covalent

Polar Covalent Bonds A polar covalent bond occurs between nonmetal atoms. It is an unequal sharing of electrons. has a moderate electronegativity difference. Examples Electronegativity Atoms Difference Type of Bond O-Cl 3.5 − 3.0 = 0.5 Polar covalent Cl-C 3.0 − 2.5 = 0.5 Polar covalent O-S 3.5 − 2.5 = 1.0 Polar covalent

Dipoles and Bond Polarity A polar covalent bond becomes more polar as the difference in electronegativity increases. The separation of charges in a polar bond is called a dipole. The positive and negative ends of the dipole are located by using the lowercase Greek letter delta with a positive or negative charge. an arrow that points from the positive to the negative end of the dipole.

Ionic Bonds An ionic bond occurs between metal and nonmetal ions. is a result of electron transfer. has a large electronegativity difference (1.8 or more). Examples Electronegativity Atoms Difference Type of Bond Cl-K 3.0 – 0.8 = 2.2 Ionic N-Na 3.0 – 0.9 = 2.1 Ionic S-Cs 2.5 – 0.7 = 1.8 Ionic

Variations in Bonding The difference in electronegativity values for two atoms can be used to predict the type of chemical bond. If the electronegativity difference is between 0 and 0.4, the bond is nonpolar covalent. between 0.5 and 1.8, the bond is polar covalent. greater than 1.8, the bond is ionic and the electrons are considered transferred.

Electronegativity and Bond Types

Predicting Bond Type Using Electronegativity

Study Check Use the electronegativity difference to identify the type of bond (nonpolar covalent [NP], polar covalent [P], or ionic [I]) between the following: A. K—N B. N—O C. Cl—Cl D. H—Cl

Solution Use the electronegativity difference to identify the type of bond (nonpolar covalent [NP], polar covalent [P], or ionic [I]) between the following: Difference Type of bond A. K—N 2.2 ionic (I) B. N—O 0.5 polar covalent (P) C. Cl—Cl 0.0 nonpolar covalent (NP) D. H—Cl 0.9 polar covalent (P)