AP Chemistry - 3.1

E_ch

energy stored in bonds - “intramolecular” forces

E_th

thermal/kinetic energy

E_ph

”phase” energy - attractions between neighboring molecules

Is there a temperature change during a phase change?

NO

What is viscosity?

how thick the liquid is

ion -dipole

attraction between an ion and a polar molecule

Dipole-induced dipole

a polar molecule induces a dipole in a nonpolar molecule

Does branching increase or decrease intermolecular forces?

decreases

What properties do intermolecular forces affect?

Usually physical properties such as boiling point, melting point

T or F: Intermolecular forces are normally weaker than covalent and ionic bonds.

True

What do intramolecular forces affect?

reactivity

What happens when electrons are lopsided in an atom?

instantaneous dipole

What are induced dipoles?

When a dipole influences another atom to experience a dipole

T or F: all molecules exhibit London dispersion forces

True

What IMFs do nonpolar molecules exhibit?

London dispersion forces

The more electrons a molecule has the more _ it is

Polarizable

The more polarizable a molecule is, the stronger its ____

LDFs

In what case are intermolecular forces stronger than those of some polar molecules?

molecules have so many electrons and are so polarizable

Polar molecules exhibit what kind of forces?

Dipole-dipole forces are stronger than LDFs. If there’s a similar number of electrons, would a nonpolar or polar molecule have a higher b.p?

Polar molecule

What allows for hydrogen bonding in water molecules?

Why is hydrogen bonding strong?

small molecules with electronegativity differences that allow for tight packing

Types of hydrogen bonds

O-H, N-H, F-H

Rank the following forces based on strength: LDF, electrostatic, simple dipole-dipole, and hydrogen

LDF < Dipole-dipole < hydrogen < electrostatic

Why do polar molecules with F, O, or N usually dissolve in water?

they can hydrogen-bond with water itself

Justify why NH3 dissolves in water but PH3 does not.

NH3 can hydrogen bond with water because the nitrogen atom is small and highly electronegative.

Why do ions stick together

electrostatic(ionic forces)

Between two nonpolar molecules, how do you decide which has stronger/more LDFs?

one with more electrons, since it is more polarizable and will have stronger forces

When do ionic compounds dissolve?

When polar molecules (like water) surround ions and pull them away from the ionic crystal lattice

Example of Ion-dipole force

H2O’s negative oxygen pole is surrounded by positive Na poles

Will the ionic compound dissolve if the ion-dipole force is greater than the electrostatic force?

Yes

When will ionic compounds dissolve?

when the ion-dipole force (i.e., H2O’s oxygen pole and Na+) is greater than the electrostatic forces (Na+ Cl-)

T or F: Insoluble ions have greater forces between ions than they would ion-dipole forces.

T

What are

Can nonpolar molecules dissolve in water?

Yes

Dipole-induced dipole forces occur between what?

Polar molecules and nonpolar molecules