1. Liquids
And
Solids

2. Properties of Liquids
Surface tension is the resistance of a liquid to an increase in its surface area.
Strong intermolecular forces (polar molecules)
High surface tension
To increase a liquid’s surface area, molecules must move from the interior of the liquid to the surface.
Requires energy since intermolecular forces must be overcome.

3. Properties of Liquids
Capillary action – spontaneous rising of a liquid in a narrow tube.
Cohesion is the intermolecular attraction between like molecules
Adhesion is an attraction between unlike molecules
Adhesion
attracted to glass
Cohesion
attracted to each other

4. Properties of Liquids
Viscosity is a measure of a liquid’s resistance to flow.
Strong intermolecular forces
High viscosity

5. Structures and Types
of Solids

6. Solids
Two categories
Amorphous solids – considerable disorder in their structures.
Crystalline solids – highly regular arrangement of their components.
Lattice – three dimensional system of points designating the positions of the components that make up the crystal.
Unit Cell – smallest repeating unit of a lattice.
lattice
point
At lattice points:
Atoms
Molecules
Ions
Unit Cell
Unit cells in 3 dimensions

7. Types of Crystalline Solids
Ionic Solids – Ion-Ion interactions are the strongest (including the “intermolecular forces” (H bonding, etc.)
Lattice points occupied by ions
Held together by electrostatic attraction
Hard, brittle, high melting point
Poor conductor of heat and electricity
CsCl
ZnS
CaF2

8. Types of Crystalline Solids
Network Atomic Solids – Stronger than IM forces but generally weaker than ion-ion
Lattice points occupied by atoms
Held together by covalent bonds
Hard, high melting point
Poor conductor of heat and electricity
carbon
atoms
diamond
graphite

9. Types of Crystalline Solids
Metallic Atomic Solid – Typically weaker than covalent, but can be in the low end of covalent
Lattice points occupied by metal atoms
Held together by metallic bonds
Soft to hard, low to high melting point
Good conductors of heat and electricity
Cross Section of a Metallic Crystal
nucleus &
inner shell e-
mobile “sea”
of e-

10. Metal Alloys
An alloy is defined as a substance that contains a mixture of elements and has metallic properties
Classified into two types:
Substitutional alloy
Interstitial alloy

11. Substitutional alloy
Some host metal atoms replaced by other metal atoms of similar size.
For example, in brass, approximately one-third of the atoms in the host copper metal have been replaced by zinc atoms.
Interstitial alloy
Some of the interstices (holes) in the closest packing structure are occupied by small atoms.
Steel, the best-known interstitial alloy, contains carbon atoms in the holes of an iron crystal.

12. Types of Crystalline Solids
Molecular Crystals
Lattice points occupied by molecules
Held together by intermolecular forces
Soft, low melting point
Poor conductor of heat and electricity
Sulfur
crystals
Phosphorus
crystals