Fundamental difference between states of matter is…
… the distance between particles.
Condensed phases
Liquids and solids
* Because particles are closer together
The state a substance is in at a particular temperature and pressure depends on two antagonistic entities:
- The kinetic energy of the particles.
* The strength of the attractions between the particles.
Gas - characteristic properties
- Assumes both volume and shape of its container
- Expands to fill its container
- Is compressible
- Flows readily
- Diffusion within a gas occurs rapidly
Liquid - characteristic properties
- Assumes shape of portion of container it occupies
- Does not expand to fill its container
- Is virtually incompressible
- Flows readily
- Diffusion within a liquid occurs slowly
Solid - characteristic properties
- Retains own shape and volume
- Does not expand to fill its container
- Is virtually incompressible
- Does not flow
- Diffusion within a solid occurs extremely slowly
Intramolecular bonds (covalent bonds) are: strong/weak?
Strong
Attractions between molecules (intermolecular bonds) are: strong/weak?
Weak
Physical properties that are controlled by intermolecular attraction
- Boiling point
- Melting point
- Vapor pressure
- Viscosity
van der Waals forces (what are they)
Intermolecular forces, collectively
van der Waals forces (3)
- Dipole–dipole interactions
- Hydrogen bonding
- London dispersion forces
London dispersion forces (describe)
(or, dispersion forces), are attractions between an instantaneous dipole and an induced dipole
* Electrons on atoms or molecules, even if nonpolar, tend to cause electrostatic attraction between other atoms or molecules due to electrons being repelled to one side (instantaneous dipole), exposing a positive side, which in turn attracts electrons on the other atom or molecule (induced dipole)
Polarizability
The tendency of an electron cloud to distort into dipoles, whether in polar or nonpolar molecules.
Factors Affecting London forces
- Shape of the molecule. The greater the surface area (long & skinny vs. round), the greater the dispersion forces.
- Molecular weight. Larger atoms have larger electron clouds that are easier to polarize.
Dipole-dipole Interactions (describe)
- Molecules that have permanent dipoles are attracted to each other.
- The positive end of one is attracted to the negative end of the other, and vice versa.
- These forces are only important when the molecules are close to each other.
Effect of molecular polarity on the boiling point
The more polar the molecule, the higher its boiling point.
Which Have a Greater Effect: Dipole–Dipole Interactions or Dispersion Forces?
- If two molecules are of comparable size and shape, dipole–dipole interactions will likely be the dominating force.
- If one molecule is much larger than another, dispersion forces will likely determine its physical properties.
Hydrogen bonds (describe and explain)
- The dipole–dipole interactions experienced when H is bonded to N, O, or F.
- Hydrogen bonding arises in part from the high electronegativity of nitrogen, oxygen, and fluorine. Also, when hydrogen is bonded to one of those very electronegative elements, the hydrogen nucleus is exposed.
Ion-Dipole Interactions (describe)
- Positive ends of polar molecules are attracted to negatively-charged anions.
- Negative ends of polar molecules are attracted to positively-charged cations.
- Is what makes it possible for ionic substances to dissolve in water (ions are surrounded by water molecules).
List all 5 forces in ascending order of strength of the bond
- Dispersion forces only
- Dipole-dipole forces
- Hydrogen bonding
- Ion-dipole forces
- Ionic bonding
Viscosity (definition and description)
- Resistance of a substance to flow (the ease with which molecules can move past each other).
- Increases with stronger intermolecular forces and decreases with higher temperature.
Surface tension (definition and explanation)
- The net inward force experienced by the molecules on the surface of a liquid.
- On surface molecules, there is no upward force to cancel the downward force, so each molecule feels a net “downward” pull.
- On interior molecules, there is pull in all directions, so each molecule feels no net pull in any direction.
Heat of fusion
The energy required to change a solid at its melting point to a liquid.
Heat of vaporization
The energy required to change a liquid at its boiling point to a gas.
