Chapter 2: Intermolecular Forces and Application on Boiling Point and Melting Point

Chem 203

How do INTERmolecular forces differ from INTRAmolecular forces?

Inter is interactions BETWEEN molecules; intra is interactions WITHIN molecules (for instance covalent bond)

By WHAT is the strength and type of interactions influenced by?

Functional groups

When it comes to IONIC compounds, what is the STRENGTH of the interactions that hold the particles together?

The interactions are STRONGLY electrostatic

What does it mean when DISPERSION forces are present?

-WEAKEST forces are present since there is a MOMENTARY CHANGE of electron density

How are dispersion forces able to hold a molecule together even though they are the WEAKEST attraction?

There are temporary dipoles within the molecule that all accumulate enough attraction

What two criteria influences dispersion forces?

Surface area and polarizability

How does surface area relate to dispersion force strength?

Stronger dispersion forces are exhibited by LONG CHAIN ISOMERS while branched isomers have WEAKER dispersion forces

How does polarizability affect dispersion force?

Larger atoms will be MORE polarizable than smaller atoms

What is the definition of polarizability?

How the electron cloud surrounding an atom responds to the change in the electronic environment

How are dipole-dipole forces different from dispersion forces?

Dipole-dipole has PERMANENT dipoles while dispersion forces only have MOMENTARY dipoles. Additionally, dipole-dipole involves TWO polar molecules

How does hydrogen bonding work?

Hydrogen ALREADY bonded to O,N, or F is attracted to a LONE PAIR of electrons on SEPARATE O,N, or F atom in a SECONDARY molecule

What is a key rule to remember when relating intermolecular forces and boiling point?

The HIGHER the IMF, the HIGHER the bp

What is the relationship between intermolecular forces and melting point?

When the compound is more symmetrical/branched, MORE energy is needed to push the HIGHER mp. Order of the solid is packed more TIGHTLY in a solid