3.1-3.3 AP Chem

Intermolecular Forces

are the attractive forces that hold the molecules and atoms of a substance together (don’t make up molecule, they only exist between molecules)

-These forces play a role in the properties of the substance. Such as the temperatures it freezes and boils at, or the surface tension, viscosity, hardness and any other physical properties. 

London Dispersion or Dispersion Forces

Weakest type, arising from temporary, instantaneous dipoles in all molecules due to the random movement of electrons.

-exists in everything

Dipole- Dipole Interaction

Attractions between the positive end of one polar molecule and the negative end of another.

Hydrogen Bonding

A special, strong type of dipole-dipole interaction that occurs when a hydrogen atom is bonded to a highly electronegative atom (like nitrogen, oxygen, or fluorine).

Induced dipole 

a temporary separation of positive and negative charges in an atom or nonpolar molecule caused by an external electric field. This effect can be caused by a nearby permanent dipole or ion, which distorts the electron cloud, creating an attraction between the molecules.

Ion Dipole

an electrostatic force between a charged ion and a polar molecule. A positive ion will attract the partially negative end of a polar molecule, while a negative ion will attract the partially positive end.

Dipole Induced Dipole

An ion creates a temporary dipole in a nonpolar molecule by disturbing its electron cloud. This results in a weak attraction between the ion and the induced dipole, contributing to intermolecular forces.

Solids

-particles don’t have enough kinetic energy to move freely

-crystilline solids have 3D structure

-amorphous solids have disordered particles 

Liquids

For liquids, the particles are still close together. However, the molecules have gained enough kinetic energy for them to slide and roll around.

-enables liquids to take the shape of their container.

-The close contact of the particles results in liquids being unable to compress.

- Solids and liquids of the same substance are often approximately the same size because the particles are close together in both states.

-The temperature range where a substance is a liquid is determined by the strength of the intermolecular forces, including hydrogen bonding, dipole-dipole, and London dispersion forces.

-The temperature range where a substance is a liquid can be compared by analyzing the strength of these forces.

Gases

-In gases, the particles have gained enough kinetic energy to overcome the intermolecular forces holding the particles together.

-This results in particles being far apart and moving quickly. Because the particles are far apart, gases can be easily compressed.

-They take the shape of their container as the particles can move freely. There is no regular arrangement of the particles.

-The frequency and strength of collisions between particles and the container is dependent on the temperature, pressure, and volume.

Triple Point

Critical point

A condition in temp and pressure where a substance can exist in all three phases. 

Critical point

a state when the liquid and gas become the same.

vapor pressure 

 a measure of the tendency of a material to change into the gaseous or vapour state