Ionic Compounds

Chapter 14 pp. 373 - 386

Chapter 5 pp. 109 - 130

Ionic Bonding The forces of attraction that bind

oppositely charged ion together Q: Where does this attraction come

from? A: Positively charged ions and

Negatively charged ions Ionic compounds are electrically neutral Also called salts

Formula Unit

Chemical formula for ionic compounds The smallest sample of an ionic

compound that has the composition of the compound.

NaCl = 1 Na atom + 1 Cl atom

How do we know how many of each ion combine with another ion?

Remember, charges in an ionic compound must be neutral

Example

Br -1

AlBr3Al3+ Br -1

Br -1

e-

e-e-

Let’s look at page 381

Try questions 9, 10, & 11

Properties of Ionic Compounds

When looking at ionic compounds we often will see that they are crystalline

A repeating 3-dimensional pattern is formed…

Coordination Number

The number of ions of opposite charge that surround each ion in a crystal

Example

NaCl - 6

How do we know the coordination number?

X-ray crystallography Patterns form when X-rays pass

through a crystal onto X-ray film Patterns are used to calculate the

position of ions in the crystal

Electric Current

Some compounds conduct electric current when dissolved in solution.

Some compounds conduct an electric current in the molten state.

How does this happen? When a current is passed through a

solution cations and anions polarize or migrate to one electrode

Electric Current continued.

Ions move to the poles opposite to their charge.

The current is passed between two electrodes

Let’s take a look at a demonstration...

Metallic Bonding

Consist of the attraction of free-floating valence electrons for the positively charged metal cations

These electrons are floating around the cations

These moving electrons effect the physical and chemical properties of metals

Metallic Bonding cont’d.

Metals can change shape because of electrons surrounding the ions

Example: ductility Ionic crystals break in

“cleavage plains” because particles of the same charge come near each other, thus repelling one another

Metals and Electrical Conductivity

Metals conduct electricity because electrons are passed from one end of the metal to another

As e- are added to one end of the metal, more e- are leaving at the other end of the metal

Shapes of Metals

Body-centered cubic– every atom has 8 neighbors

Face-centered cubic– every atom has 12 neighbors

Hexagonal close-packed– every atom has 12 neighbors, but different

arrangement from Face-centered Page 385 - Fig. 14.12