States of Matter

Part 3

Liquids

• Kinetic-molecular theory can be applied to liquids

• Predicts that molecules of a liquid are in constant motion– Forces of attraction limit the range of

movement so that the molecules remain in a fixed volume

Properties of liquids

• Density and compression– At 25°C and 1 atm of pressure, the density of

a liquid is much greater than the density of a gas.

– Because they are at the same temperature, the KE is the same

– The intermolecular forces result in a greater density

Properties of liquids

• Fluidity– The ability to flow– Liquids and gases flow– Liquids diffuse much more slowly, because

the intermolecular forces interfere– Liquids are less fluid than gases

Properties of liquids

• Viscosity– A measure of the resistance to flow– The stronger the intermolecular forces the

higher the viscosity– The larger the molecule the higher the

viscosity– Viscosity decreases with increasing

temperature

Properties of liquids

• Surface tension– Measure of the inward pull by particles in the

interior– The stronger the attraction of the particles, the

greater the surface tension– Surfactants act to break the hydrogen bonds

of water to decrease the surface tension

Properties of liquids

• Capillary Action– Occurs when adhesion is greater than

cohesion– Cohesion

• Force of attraction between identical molecules

– Adhesion• Force of attraction between different molecules

– Explains how plants get water up stems– Explains how paper towels absorb water

Solids

• According to Kinetic-molecular theory, solids have the same KE as liquids and gases at the same temperature

• Solids are therefore in constant motion

• Strong intermolecular forces limit the motion to vibrations

• Solids are not fluid and do not flow

Density of solids

• Most solids are more dense than their liquid

• Water is an exception

Crystalline Solids

• A solid whose atoms, ions or molecules are arranged in an orderly, geometric, three-dimensional structure

• Individual pieces are called crystals• Five types of crystalline solids:

– Atomic, molecular, covalent network, ionic and metallic

– Shape is determined by the unit cell – smallest arrangement of connected points that can be repeated in three directions (see p400 for examples)

Amorphous Solids

• Solids that are not arranged in a repeating predictable pattern

• Not crystals

• Glass, rubber and many plastics

Practice

1. Explain how hydrogen bonds affect viscosity. How does a change in temperature affect viscosity?

2. What effect does soap have on the surface tension of water?

3. Explain why the surface of water in a graduated cylinder is curved.

4. Explain why water has a higher surface tension than benzene, which is non-polar.