Intermolecular forces, Intermolecular Forces

polar molecule

molecule that has an overall dipole moment

Intramolecular forces

forces that hold the atoms together in a molecule

Intermolecular forces

interactions between molecules (much weaker)

intermolecular force strength

measures by: boiling and melting point- the higher, the stronger the forces

Types of Van der Waals forces:

Dipole-dipole

Ion-dipole

Dipole-induced Dipole

Dispersion

Dipole-dipole forces

forces between polar molecules (partially charged)- opposite poles match up by electrostatic attraction

Ion-dipole forces

forces between a fully charged species (ion) and a dipole by electrostatic attraction.

Increase in strength with increase in charge or decrease in size of ion

(how ions are dissolved in water- attract to the H2O and pulled away by electrostatic charge)

Dipole-induced-dipole forces

forces arising from temporary dipoles induced in atoms by ions with a permanent dipole (either ion or dipole).

Temporary dipoles created when non-polar molecule interacts with polar- temporarily shifts the electrostatic charge to attract the polar molecule, then returns when removed

Dispersion forces

Weak force- Occurs between all non-polar molecules due to their electron density.

- Collision of 2 non-polar molecules causes their electrostatic regions to shift temporarily (creating induced dipoles) and the molecules are instantaneously attracted

- Increase with molar mass

Polarizability

Ease with which the electron distribution in a molecule can be distorted

Increases with:

- greater number of electrons

- more diffuse electron cloud

Hydrogen bonds

A special dipole-dipole interaction between a Hydrogen atom and either N, O, or F atom (smallest and most electronegative on PT)

- the lone pair on either N, O, F (in a molecule) is what causes the bond- strongest interaction with H

- reason why solid form of water floats on liquid form- H bonds- once frozen becomes less dense than liquid

surface tension

Surface tension is the amount of energy required to stretch the surface area of a liquid by unit area

- strong intermolecular force = strong surface tension

viscosity

Measure of fluids resistance to flow

- strong intermolecular force = high viscosity

solubility

- Polar compounds dissolve other polar compounds

- Non-polar compounds dissolve non-polar

- Polar compounds insoluble in non-polar

Intermolecular Force

Force between molecules

Intramolecular Force

Force within a molecule

Covalent Bond

Force of attraction within a molecule created by the sharing of electrons

Ionic Bond

Force of attraction created by the transfer of electrons between atoms

Polar Molecule

Molecule in which the covalent bonds are asymmetrically arranged

Nonpolar Molecule

Molecule in which the covalent bonds are symmetrically arranged

London Dispersion Force

Intermolecular force between nonpolar molecules

Dipole-Dipole Force

Intermolecular force between polar molecules

Hydrogen Bond

Intermolecular force between molecules containing hydrogen bonded to N, O, or F

Surface Tension

The force exerted along the surface of a fluid that causes it to "bead up" and form into drops

Vapor Pressure

Pressure exerted on the surface of a liquid by the vapor

Direct relationship

Relationship between strength of intermolecular force and boiling point

Inverse relationship

Relationship between the strength of the intermolecular force and the vapor pressure

Boiling point

Temperature at which the vapor pressure is equal to the atmospheric pressure

Water

Substance exhibiting hydrogen bonding

hydrocarbons

Substance exhibiting London dispersion forces

Carbon monoxide

Substance exhibiting dipole-dipole forces