Properties of Liquids

Reminder: Kinetic-molecular Theory says the particles of matter are always in motion

I. Properties of Liquids & the Kinetic-Molecular Theory

A. Compared to Gases:1. Particles in liquids are closer together2. Attractive forces between liquid particles are

more effective (polarity & hydrogen bonds)3. Particles are not bound together in fixed positions4. Fluid: substance that flows and takes shape of its

container

Gas Particles Liquid Particles

B. Other Properties of Liquids1. Relatively high density (much more dense

than gases as particles are closer together)2. Relative Incompressibility – liquids are much

les compressible than gases (again, particles are closer together)

3. Diffusion – any liquid gradually diffuses throughout any other liquid in which it can dissolve• Constant, random motion causes diffusion• Slower in liquids than gases, particles are

closer together

B. Other Properties of Liquids4. Surface Tension – force that tends to pull

adjacent parts of a liquids surface together, thereby decreasing surface area to the smallest possible size• Capillary Action: surface of liquid is

attracted to the surface of a solid• Allows liquids to travel through narrow

tubes, even against gravity!

Surface Tension

B. Other Properties of Liquids5. Evaporation & Boiling• Vaporization: process of a liquid or solid

changing to a gas• Evaporation: process by which particles

escape from the surface of a nonboiling liquid and enter the gas state

• Boiling: the change of a liquid to bubbles of vapor that appear throughout the liquid

6. Formation of Solids – the physical change of a liquid to a solid by removal of heat energy is freezing

Properties of Solids

I. Properties of Solids & the Kinetic-Molecular Theory

A. Intermolecular Forces1. Much more effective in solids2. Keeps particles very close together3. Holds particles in a relatively fixed position,

with only vibrational movement around fixed points.

4. For all these reasons, solids are more ordered than liquids, and much more ordered than gases.

B. Two Types of Solids1. Crystalline Solids – consist of crystals, a

substance in which the particles are arranged in an orderly, geometric, repeating pattern

2. Amorphous Solid – particles are arranged randomly (glass & plastics)

B. Other Properties of Solids1. Definite Shape and Volume• Maintain shape without a container• Crystalline solids are geometrically regular• Amorphous solids have no distinct

geometric shapes (glass can be molded)• Volume changes only slightly with

temperature/pressure changes

2. Definite Melting Point• Melting: physical change of a solid to a

liquid by adding heat energy• Melting Point: temperature at which a solid

becomes a liquid; kinetic energies of the particles overcome the attractive forces holding them together

• Amorphous solids do not have definite melting points, can flow over a range of temperatures

• Amorphous solids are classified as supercooled liquids, which retain certain liquid properties but appear to be solid

3. High Density & Incompressibility• Generally, substances are most dense in

the solid state• Solids are slightly more dense than liquids

and much denser than gases.• Solids are not compressible• All is due to the particles of solids being

closely packed together4. Low Rate of Diffusion• Rate of diffusion is millions of times slower

in solids than in liquids

II. Crystalline SolidsA. Ionic Crystals - made of positive & negative ions

1. Hard, brittle, high melting points, good insulators

B. Covalent Network Crystals - atoms are covalently bonded to their neighbors1. Hard, brittle, high melting points,

nonconductors or semiconductors

C. Metallic Crystals - made of metallic cations surrounded by electrons1. High electric conductivity

D. Covalent Molecular Crystals - molecules are held together by intermolecular forces1. Soft, low melting points, easily vaporized,

good insulators