Chapter 10, Section 2  LIQUIDS

Liquids & Kinetic-Molecular Theory  1. Liquid particles are closer together than gas particles.

Liquids & Kinetic-Molecular Theory  2. More ordered arrangement than gases.

Liquids & Kinetic-Molecular Theory  3. Attractive forces exist between liquid particles. (Remember: this is not true of ideal gases.) These forces hold liquids together.

FLUID  Liquids, like gases, can flow and therefore take the shape of their container.

Properties of Liquids  1. Relatively high density.

Properties of Liquids  2. Relative incompressibility

Properties of Liquids  3. Ability to diffuse due to constant random motion. Diffusion is slower than in gases.

Properties of Liquids  4. Surface Tension: a force that pulls adjacent parts of a liquid’s surface together, thereby decreasing surface area to the smallest possible size.

Capillary Action  The attraction of the surface of a liquid to the surface of a solid.

GAS vs VAPOR  Vapor refers to the gaseous state of a substance that is normally a liquid or solid at ROOM TEMPERATURE.

VISCOSITY  A measure of a liquid’s resistance to flow.

VAPORIZATION  The conversion of a liquid or solid to a gas or vapor

EVAPORATION  Process by which particles escape from the surface of a NONBOILING liquid and enter the gas state.

 Only molecules with KE above a certain minimum amount can escape.

COOLING EFFECTS  Molecules with highest KE escape first.  Those left behind have lower KE; temperature of the liquid decreases.

FREEZING:  The physical change of a liquid to a solid by removal of energy as heat.  As a liquid cools, the KE decreases & particles are pulled together in a more orderly arrangement – a solid.

BOILING:  Vaporization (appearance of bubbles) throughout a liquid.

VAPOR PRESSURE  The force exerted by the gas above a liquid in a closed container.  Increasing temperature increases vapor pressure

DYNAMIC EQUILIBRIUM  The point when the rate of evaporation equals the rate of condensation.

BOILING POINT  The temperature at which the vapor pressure of the liquid is just equal to the external pressure.

NORMAL BOILING POINT  The boiling point at kPa of pressure

INTERMOLECULAR FORCES  Attraction between molecules.  Generally weaker than bonds in a molecule

3 types of IM forces  1. Dipole-Dipole Forces  2. Hydrogen bonding  3. London Dispersion Forces

Dipole-Dipole Forces  Strongest IM force  Occurs between polar molecules  Equal but opposite charges separated by a short distance creates a dipole.

Hydrogen Bonding  A Hydrogen atom that is bonded to a highly electronegative atom is attracted to an unshared pair of electrons of an electronegative atom in a nearby molecule.

Hydrogen bonding (cont.)  H is small; can get very close to the unpaired electrons  Strong intermolecular force  Unusually high boiling points for molecular compounds

London Dispersion Forces  Electrons are constantly moving – can be distributed unequally.  Creates a temporary dipole  Weak forces

London Dispersion Forces  The IM attractions resulting from the constant motion of electrons and the creation of instantaneous temporary dipoles.

London Dispersion Forces  LDF are present between ALL atoms and molecules.  For NOBLE GASES and NONPOLAR MOLECULES, London Dispersion Forces are the ONLY IM force