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Chapter 10 Structures of Solids and Liquids

10.3

Electronegativity and Polarity

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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

Electronegativity

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Some Electronegativity Values for Group A Elements

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Learning Check

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

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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

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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

NN 3.0 - 3.0 = 0.0 Nonpolar covalent

ClBr 3.0 - 2.8 = 0.2 Nonpolar covalentHSi 2.1 - 1.8 = 0.3 Nonpolar covalent

Nonpolar Covalent Bonds

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A polar covalent bond • occurs between nonmetal atoms• consists of atoms that share electrons unequally• has an electronegativity difference range of 0.5

to 1.7Examples:

Atoms Electronegativity Type of Bond Difference

OCl 3.5 - 3.0 = 0.5 Polar covalentClC 3.0 - 2.5 = 0.5 Polar covalentOS 3.5 - 2.5 = 1.0 Polar covalent

Polar Covalent Bonds

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Comparing Nonpolar and Polar Covalent Bonds

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Ionic BondsAn 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 ClK 3.0 – 0.8 = 2.2 Ionic

NNa 3.0 – 0.9 = 2.1 Ionic

SCs 2.5 – 0.7 = 1.8 Ionic

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Electronegativity and Bond Types

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Predicting Bond Types

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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 OC. Cl and ClD. H and Cl

Learning Check

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Atoms in Electronegativity Type of Bond Difference BondA. 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)

Solution

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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

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Nonpolar Molecules

A nonpolar molecule • may contain identical atoms (nonpolar bonds)

• may have a symmetrical arrangement of polar bonds that cancel dipoles

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Determining Molecular Polarity

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

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Learning Check

Identify each of the following molecules as

(P) polar or (NP) nonpolar:

A. PBr3

B. HBr

C. Br2

D. SiBr4

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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