chapter 13 the chemistry of solids

Chapter 13 The Chemistry of SolidsTypes of Solids

• Metals• Network• Ionic • Molecular• Amorphous

Chapter 13 The Chemistry of SolidsTypes of Solids Examples

• Metals Copper• Network Quartz• Ionic NaCl • Molecular CO2, CI4• Amorphous glass, polyethylene

Types of Solids Characteristics

• Metals Copper - malleable

• Network Quartz – non-malleable

• Molecular sulfur (S8)• CO2, CI4 – low melting pt

• Ionic & muscovite– cleaves easy Network, Layered structure

The Chemistry of SolidsWhat characteristic do these solids share?

The Chemistry of SolidsWhat characteristic do these solids share?

Repeating Structural Patternother terms:LatticeArrayCrystal Structure orCrystal Lattice

The Chemistry of SolidsUNIT CELL is the smallest piece of the pattern that generates the lattice.

UNIT CELL is a conventional choice.May have several unit cells possible,Different in shape and/or size.

Translation directions

The Chemistry of SolidsUNIT CELL is a conventional choice.May have several unit cells possible,Different in shape and/or size.

Three Types of Cubic Unit Cells

a

cb

Simple Cubic Body Centered Cubic

Face CenteredCubic

These Three Cubic Unit Cells are Structuresof most Metallic Elements(also hexagonal, hcp, to be seen Friday)

Cu, Ag, Au are all fccCr, Mo, W are all bccOnly Po is simple cubic (rare— why?)

Simple Cubic Body Centered Cubic

Face CenteredCubic

One result of a metal’s “choice” to adopt a cubic, bcc or fcc lattice are metal properties

Simple Cubic Body Centered Cubic Face Centered Cubic

Packing a Square Lattice:

Makes a simple cubic cell

Can you pack spheres more densely?

The Rhomb is the Unit Cell Shapeof Hexagonal Lattices

Closest Packing: hexagonal layers build up 3D solid

Find the triangular gaps in the Pink layer

Note how layers “sit” on top of each other:

The Cyan layercovers the “up”triangles of thePink layer

The Yellow layercovers the “down”triangles of thePink layer

This packing sequence is A B C A B C,Where B and C cover different “holes” in A

BC

A

BC

A

BC

A

BC

APa

ckin

g di

rect

ion A

C B A C B A

ccp CubicClosestPacking:A B C A B C …

Packing direction

CCP viewed unit cell;

LOOK! It’s face centered cubic!!! CCP = FCC!!

….mmmMMM

CCP viewed as packing layers

AB

C

CBA

Effect of addedatoms andgrainson metal structure.

Smaller atom like C in iron

Larger atom like P in iron

Second crystal phasesprecipitated

Defects and grain boundaries “pin” structure. All these inhibit sliding planes and harden the metal.

Defectsin metal structure

From Metals to Ionic Solids

Will ionic solids pack exactly like metallic solids?

From Metals to Ionic Solids

Build up Ionic Solids conceptually like this:• assume Anions are larger than Cations, r- > r+• pack the Anions into a cubic lattice: ccp, simple or bcc• add Cations to the interstitial spaces (“Mind the gap!”)

2 x r-

2 x r-

r- + r+

The Simplest Ionic Solid is CsCl, simple cubic

Start withsimple cubicUnit cell of Cl- ions

Then add one Cs+ in center

Z =C. N. (Cs) =

How to draw this

How to make NaCl: start with fcc unit cell of Cl- ions

Add Na+ in between

Add Na+ in between, everywhere

Z =C. N. (Na) =