ch. 12 - solids and modern materials

four predominant classifications for solids

1. metallic solids
2. ionic solids
3. covalent-network solids
4. molecular solids

metallic solids

* metal atoms held together by a “sea” of collectively shared valence electrons
* allows metals to conduct electricity
* makes metals strong w/o being brittle

ionic solids

* anions and cations held together by mutual electrostatic attraction
* do not conduct electricity well; are very brittle

covalent-network solids

* atoms are held together by an extended network of covalent bonds (shared e⁻)
* results in extremely hard materials (diamond)
* responsible for semiconductor properties

molecular solid

* discrete molecules held together by IMFs
* soft solids w/ low melting points (ice)

polymers

* long chains of (usually carbon) atoms connected by covalent bonds w/ chains held together by IMFs
* stronger w/ higher melting points than molecular solids
* more flexible than metallic, ionic, or covalent solids

nanomaterials

* solids in which the dimensions of individual crystals are 1-100nm

crystalline solids

* solids in which atoms are arranged in an orderly repeating pattern
* usually have flat surface/face that leads to a highly regular shape
* ex. NaCl, quartz, diamond, pyrite

amorphous solids

* solids that lack order, are structurally similar to liquids but lack freedom of movement
* ex. rubber, glass, obsidian

unit cell

* the smallest group of atoms in a unique arrangement that can be repeated to embody the whole structure of a solid

crystal lattice

* unit cells stacked over and over to create the structure of the solid

crystalline solids structure are defined by

1. size and shape of unit cell
2. location of atoms within the unit cell

2-D

oblique

2-D

square

2-D

rectangle

2-D

hexagonal

2-D

rhombic

3-D

cubic

3-D

tetragonal

3-D

orthorhombic

3-D

rhombohedral

3-D

hexegonal

3-D

monoclinic

3-D

triclinic

primitive/simple

body-centered

face-centered

primitive/simple cubic

* have atoms only in the lattice points

centered lattices

* have atoms at lattice points at the corners

body center cubic

* have one lattice point in the center of the cell

face center cubic

* have one lattice point at the center of each face

simple case

* identical atoms
* atoms are at lattice points
* only possible for elements

motif

* a group of atoms

corners contain

* 1/8 of an atom

face contains

* 1/2 of an atom

center contains

* 1 whole atom

alloys

* contain more than one element and have properties of a metal
* allow us to modify properties of pure metallic elements
* ex. pure gold is too soft to be used in jewelry

substitutional alloy

* atoms of a solute occupy positions normally occupied by a solvent atom
* similar atomic radii

interstitial alloy

* solute atoms occupy “holes” between solvent atoms
* often a nonmetal, much smaller atomic radius