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Bond Character and Molecular Polarity

How does atom electronegativity affect bond character and molecular polarity?

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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The electronegativity value

• measures an atom’s tendency to attract electrons from other atoms

• is higher for nonmetals than for metals

• Why does this happen?

• What is going on in the atom with Coulombic attraction?

Electronegativity

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Some Electronegativity Values for Group A Elements

Low values

High values

` Electronegativity increases

` E

lectrone

gativity d

ecrease

s

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A nonpolar covalent bond

• occurs between nonmetals• is an equal or almost equal sharing of electrons• has almost no electronegativity difference (below 0.4)

Examples: Electronegativity Atoms Difference Type of BondN-N 3.0 - 3.0 = 0.0 Nonpolar covalent

Cl-Br 3.0 - 2.8 = 0.2 Nonpolar covalentH-Si 2.1 - 1.8 = 0.3 Nonpolar covalent

Nonpolar Covalent Bonds

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Nonpolar Covalent Bond

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A polar covalent bond

• occurs between nonmetal atoms• is an unequal sharing of electrons• has a moderate electronegativity difference (0.4 to 1.7)

Examples: Electronegativity

Atoms Difference Type of BondO-Cl 3.5 - 3.0 = 0.5 Polar covalentCl-C 3.0 - 2.5 = 0.5 Polar covalentO-S 3.5 - 2.5 = 1.0 Polar covalent

Polar Covalent Bonds

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Polar Covalent Bond

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Comparing Nonpolar and Polar Covalent Bonds

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Ionic Bonds

An ionic bond • occurs between metal and nonmetal ions• is a result of electron transfer• has a large electronegativity difference (above 1.7)

Examples: Electronegativity

Atoms Difference Type of BondCl-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

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Ionic Bond

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Use the electronegativity difference to identify the type of bond between the following:nonpolar covalent (NP), polar covalent (P), or

ionic (I).

A. K-NB. N-OC. Cl-ClD. H-Cl

Learning Check

< 0.4

Nonpolar covalent

0.4 to 1.7

Polar covalent

> 1.7

Ionic

Electronegativity Difference

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Some Electronegativity Values for Group A Elements

Low values

High values

` Electronegativity increases

` E

lectrone

gativity d

ecrease

s

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Not all molecules with polar bonds are polar

You will learn more about this when you study molecular geometry

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Crosscutting Concepts

Patterns

in chemistry, and other sciences, we are always looking for patterns

you were able to determine a pattern of nature of bonds formed when different atoms interact

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Crosscutting Concepts

Models

in chemistry, and other sciences, we often use models to help us understand phenomenon

you used a computer simulation to model the effect of changing electronegativity

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Crosscutting Concepts

Structure and Function

in chemistry, and other sciences, the way an object is shaped or structured determines many of its properties and functions

the structure of a molecule determines if it is polar or nonpolar

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Nature of Science and Scientific Inquiry

Laws vs Theories

law-behavior of natural phenomenon or generalized relationships under certain conditions

theory-well substantiated explanation of some aspect of natural world

theories do not become laws even with additional evidence

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Nature of Science and Scientific Inquiry

Data vs Evidence

data-measurements, observations, and findings collected as part of an investigation

evidence-analyzed data and interpretation of the analysis