11.3 Structures of Solids
PRE-HEALTH PREP
Solid Structures
amorphous solids – a solid with no ordered structure
Cubic Unit Cells
Simple Cubic
Atoms occupy the corners
1 atom per unit cell
Coordination Number = 6
a = 2r (a = edge length; r = radius)
Packing Efficiency = 52%
Body-Centered Cubic (BCC)
Atoms occupy the corners and body center
2 atoms per unit cell
Coordination Number = 8
√3a = 4r (a = edge length; r = radius)
Packing Efficiency = 68%
Face-Centered Cubic (BCC)
Atoms occupy the corners & face centers
4 atoms per unit cell
Coordination Number = 12
√2a = 4r (a = edge length; r = radius)
Packing Efficiency = 74%
Close-Packing of Spheres
Hexagonal Close-Packed
2 alternating layers of spheres (ABAB)
Cubic Close-Packed
3 alternating layers of spheres (ABCABC)
Bonding in Solids
Molecular Solids
Held together by intermolecular forces
Relatively low melting points
H2O: m.p. = 0ºC
C3H8: m.p. = -188ºC
Network Covalent Solids
Held together by covalent bonds
High Melting Points
Examples: Cdiamond and SiO2 (quartz)
SiO2: m.p. = 1700ºC
Ionic Solids
Held together by ionic bonds
High Melting Points
Higher charges & smaller ions lead to stronger ionic bonds & higher melting points
LiF: m.p. = 845ºC
CsF: m.p. = 682ºC
Li2O: m.p. = 845ºC
Metallic Solids
Held together by metallic bonds
