Solids

Image:Wikimedia Commons User Alchemistry-hp

Types of SolidsCrystalline

Solids: highly regular arrangement of their components

Amorphous solids: considerable disorder in their structures (glass, plastic).

Representation of Components in a Crystalline

Solid

Lattice: A 3-dimensional system of points designating the centers of components (atoms, ions, or molecules) that make up the substance.

Bragg’s Law

xy + yz = n and xy + yz = 2d sin

n = 2d sin

Crystal Structures - Cubic

a

aa

Simple Face-Centered Body-Centered

**Knowledge of specific types of crystal structures and the study of the specific varieties of crystal lattices for ionic compounds is beyond the scope of this course and the AP Exam.

Crystal Structures - Monoclinic

c

ab

Simple End Face-Centered

Crystal Structures - Tetragonal

c

aa

Simple Body-Centered

Crystal Structures - Orthorhombic

c

ab

Simple EndFace-Centered

BodyCentered

FaceCentered

Crystal Structures – Other Shapes

aa a

a120o

c

a

Rhombohedral TriclinicHexagonal

a

c

b

Closest Packing: Single Layer

Photographer : Thierry Dugnolle

Closest Packing: MultipleLayers

Model: Packing uniform, hard spheres to best use available space. This is called closest packing. Each atom has 12 nearest neighbors.

Metal Alloys

Substitutional Alloy: some metal atoms replaced by others of similar size.• brass = Cu/Zn

Metal Alloys(continued)

Interstitial Alloy: Interstices (holes) in closest packed metal structure are occupied by small atoms.

• steel = iron + carbon

Network Atomic SolidsSome covalently bonded substances DO NOT form discrete molecules.

Diamond, a network of covalently bonded carbon atoms

Graphite, a network of covalently bonded carbon atoms

GrapheneGraphene can be described as a one-atom thick layer of graphite.

Source: Wikipedia

High-quality graphene is strong, light, nearly transparent and an excellent conductor of heat and electricity. Andre Geim and Konstantin Novoselov at

the University of Manchester won the Nobel Prize in Physics in 2010 "for groundbreaking experiments regarding the two-dimensional material graphene"

Semiconductors

Pure silicon is structurally the same as diamond, but is a semiconductor rather than an insulator. The conductivity increases at higher temperature.

Conductivity of silicon can be improved by doping with other elements.

n-type Semiconductors

Substances whose conductivity is increased by doping with atoms having more valence electrons than the host crystal. Here, silicon (4 valence e-’s) is doped with phosphorus (5 valence e-’s).

p-type Semiconductors

Substances whose conductivity is increased by doping with atoms having fewer valence electrons than the host crystal. Here, silicon (4 valence e-’s) is doped with aluminum (3 valence e-’s).

Molecular Solids

Strong covalent forces within molecules

Weak covalent forces between molecules

Sulfur, S8 Phosphorus, P4

Ionic Solids

Sodium Fluoride

Ionic compounds at room conditions are generally crystal lattices of alternating cations and anions.

Sodium chloride and sodium fluoride form simple cubic crystals.

NaCl Unit Cell

Ionic Solids

Lithium niobate, LiNbO3

Ionic compounds are represented by empirical formulas, because they do not form discrete molecular structures.