Chapter 10 Structures of Solids and Liquids 10.3 Electronegativity and Polarity

Electronegativity Electronegativity is the relative ability of atoms to attract shared electrons is higher for nonmetals, with fluorine as the highest with a value of 4.0 is lower for metals, with cesium and francium as the lowest with a value of 0.7 increases from left to right going across a period on the periodic table decreases going down a group on the periodic table

Some Electronegativity Values for Group A Elements

Learning Check Using the periodic table, predict the order of increasing electronegativity for the elements O, K, and C.

Solution The metal K on the left of Period 4 has the lowest electronegativity of the three elements. The nonmetal O on the upper right of Period 2 has the highest electronegativity. The nonmetal C, which is on the left of O in the periodic table, has a lower electronegativity than O, but a higher electronegativity than K. Order of increasing electronegativity: K, C, O

Nonpolar Covalent Bonds A nonpolar covalent bond occurs between nonmetal atoms consists of an equal (or almost equal) sharing of electrons has a zero (or close to zero) electronegativity difference of 0.0 to 0.4 Examples: Atoms Electronegativity Type of Bond Difference 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 consists of atoms that share electrons unequally has an electronegativity difference range of 0.5 to 1.7 Examples: Atoms Electronegativity Type of Bond Difference 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

Comparing Nonpolar and Polar Covalent Bonds

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: Atoms Electronegativity Type of Bond Difference 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

Electronegativity and Bond Types

Predicting Bond Types

Learning Check Use electronegativity differences to classify each of the following bonds as nonpolar covalent (NP), polar covalent (P), or ionic (I): A bond between A. K and N B. N and O C. Cl and Cl D. H and Cl

Solution Atoms in Electronegativity Type of Bond Difference Bond A. K and N 2.2 ionic (I) B. N and O 0.5 polar covalent (P) C. Cl and Cl 0.0 nonpolar covalent (NP) D. H and Cl 0.9 polar covalent (P)

Polar Molecules A polar molecule contains polar bonds has a separation of positive and negative charge called a dipole indicated by a dipole arrow has dipoles that do not cancel

Nonpolar Molecules A nonpolar molecule may contain identical atoms (nonpolar bonds) may have a symmetrical arrangement of polar bonds that cancel dipoles

Determining Molecular Polarity The polarity of a molecule is determined from its electron-dot formula shape polarity of the bonds dipole cancellation

Learning Check Identify each of the following molecules as (P) polar or (NP) nonpolar: A. PBr3 B. HBr C. Br2 D. SiBr4

Solution Identify each of the following molecules as (P) polar or (NP) nonpolar: A. PBr3 (P) pyramidal; dipoles don’t cancel; polar B. HBr (P) linear; one polar bond (dipole); polar C. Br2 (NP) linear; nonpolar bond; nonpolar D. SiBr4 (NP) tetrahedral; dipoles cancel; nonpolar