Chem 2 Quiz 1

What are intermolecular forces?

They are electrostatic forces between molecules that depend on the magnitude of σ- and σ+

Weaker than ionic or covalent bonds!

What are Dispersion Forces?

Fleeting, temporary dipoles resulting in weak electrostatic forces between molecule when very close together

Instantaneous dipoles

Result from constant motion of electrons in molecules and atoms

Induced dipoles

They result when an instantaneous dipole in one molecule or atom distorts the electrons in a neighboring atom/molecule

Polarizability

Measure of how easy or difficult it is for another electrostatic charge to distort a molecule’s charge distribution

What substances have dispersion forces?

ALL substances (polar AND nonpolar)

Why do bigger/heavier molecules/atoms exhibit stronger dispersion forces than lighter/smaller molecules and atoms?

This is because the larger atoms have a greater polarizability because they have more valence elctrons that are farther from the nucleus

Dipole-Dipole Attractions

-Present in only polar molecules

-In molecules with permanent dipoles

-Stronger with higher dipole moments

-Usually stronger than dispersion forces

-Molecules arrange to align opposite charges

Not included in van der Waals Forces

How do you determine whether a compound is polar/nonpolar from its formula/structure?

1. Draw the Lewis Structure and its shape

   1. If electrons are unbalanced, it is polar

What is the strongest intermolecular force?

Hydrogen bonding

Hydrogen bonding

It is an unusually strong type of dipole-dipole attraction

-Strongers IMF

-Present in only CERTAIN polar molecules with N—H, O—H, or F—H bonds

What is hydrogen bonding also used for?

-Maintain genetic coding/facilitate replication

-Allow wool fibers to adapt secondary structure (alpha helix) for flexibility and water absorption

-Maintain cellulose structure (cotton + flax)

What is the hierarchy for IMFs?

Chemical bonding »»»»»

Hydrogen bonding

^

Dipole-dipole

≥

Dispersion forces