Chapter 4 Compounds and Their Bonds 4.8 Attractive Forces in Compounds 1 Chemistry: An Introduction…

Chapter 4Compounds and Their Bonds

4.8Attractive Forces in Compounds

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Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Dipole-Dipole Attractions and Hydrogen Bonds

In covalent compounds, polar molecules • exert attractive forces called dipole-dipole attractions• form strong dipole attractions called hydrogen bonds between hydrogen atoms bonded to very electronegative atoms of F, O, or NHydrogen bonds are the strongest force betweenmolecules and play a major role in the shape of DNA.

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Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Dispersion Forces

Dispersion forces are• weak attractions between nonpolar molecules• caused by temporary dipoles that develop when

molecules bump into each other• weak, but make it possible for nonpolar molecules to

form liquids and solids

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Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Comparison of Bonding and Attractive Forces4

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Melting Points and Attractive Forces

Melting points • of compounds are related to the strength of attractive

forces between molecules or compounds• are lower due to weak forces such as dispersion forces• are higher due to stronger attractive forces such as

hydrogen bonding• are highest in ionic compounds due to the strong

attractive forces between ions in the compound

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Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Melting Points of Selected Substances6

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Learning Check

Identify the main type of attractive forces that are present in liquids of the following compounds: ionic bonds, dipole-dipole, hydrogen bonds, or dispersion forces.

A. NCl3

B. H2OC. Br-BrD. KClE. NH3

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Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.

Solution

Identify the main type of attractive forces that are present in liquids of the following compounds: ionic bonds, dipole-dipole, hydrogen bonds, or dispersion forces.

A. NCl3 dipole-dipole forcesB. H2O hydrogen bondsC. Br-Br dispersion forcesD. KCl ionic bondsE. NH3 hydrogen bonds

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Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc.