1. The Solid-State Structure of Metals and Ionic Compounds
Crystal Structures
The Solid-State Structure of Metals and Ionic Compounds

2. Introduction
In crystalline materials, elements repeat in repetition to give a 3D arrangement known as a crystal lattice
A unit cell is the smallest part of the lattice that represents the entire lattice (repeated part)
5 types of unit cells:
Primitive
Body-centered
Face-centered
Hexagonal close-packed
diamond

3. Introduction Face-Centered Hexagonal Diamond
Hexagonal Diamond

4. Introduction continued
There is empty space in each unit cell where the atoms don’t touch
All atoms want to pack together as close as possible, the most efficient arrangement of spheres
3 types of open holes
Tetrahedral
Octahedral
cubic
Tetrahedral hole
Cubic hole
Octahedral hole

5. Coordination Number
Crystal coordination number (CN): number of neighbors to an atom in a unit cell
Example: simple cubic is 6
Cornfused?

6. Coordination Number
Body-centered: CN of 8
Face-centered: CN of 12

7. There are FOUR Types of Crystals
Molecular crystal
Metallic crystal
Covalent crystal
Ionic crystal

8. Metallic Bonding Metals can form bonds with themselves
Very dense and compact
Think of it as positive ions in a sea of delocalized valence electrons
Delocalized electrons makes metals good conductors of heat and electricity
Sea of electrons
Metallic crystals are the simplest  every
lattice point in a crystal is the same atom
Ex: Na, Mg, Fe, Cu

9. Molecular Crystals
Lattice points are occupied by molecules and the attractive forces are van der Waals forces and/or hydrogen bonding
Soft, low melting points, poor conductors of heat and electricity, MOST ARE LIQUIDS AND GASES AT ROOM TEMPERATURE!
All nonmetals
Ex: CO2, I2, H2O

10. Covalent Crystals
Elements held together by a 3D network entirely of covalent bonds, all nonmetals
Examples: diamond (C), graphite (C), quartz (SiO2)
Very hard, high melting points, poor conductors of heat and electricity, MOST ARE SOLIDS AT ROOM TEMPERATURE!

11. Ionic Compounds Ionic crystals Usually have:
1. charged species
2. anions and cations that are quite different in size
Held together by ionic (electrostatic) bonds
Very hard, brittle, high melting point, poor conductors of heat and electricity (unless in aqueous solution)
Must have at least one metal
Ex: NaCl, LiF

12. Amorphous Solids Some solids are not crystalline at all
If a solid is formed rapidly (cooled very quickly), the atoms don’t have time to align themselves and form amorphous solids
They lack a regular 3D arrangement
One example is glass (SiO2)