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CHEMISTRY - GILBERT 5E

CH.12 - SOLIDS: STRUCTURES AND APPLICATIONS

CONCEPT: ALLOYS

An alloy represents a _________________ mixture composed of two or more elements in which at least one of the elements is a metal.

• The predominant metal component, which is can be up to 90% or higher in terms of composition is referred to as the ____________ or ____________ metal.

• The minor components, which usually average around 1% in terms of composition, are referred to as the _______________________.

Alloys can be created by three different methods:

1) Heating the alloy components into liquids, mix them together and allowing them to cool into a ____________________.

2) ____________________ : turning the components into powders, mixing them together and allowing them to fuse.

3) ____________________: firing beams of ions at the surface of the host metal and allowing other components to mix.

Alloys are classified into two major types:

• A(n) _______________________ alloy is where some of the host metal atoms have been replaced by other metal atoms that have a similar size.

• A(n) _______________________ alloy is where the empty spaces between the host metal atoms have been taken up by smaller metal atoms.

Other common alloys that are good to remember include:

______________________ – copper (host metal), tin, manganese, phosphorus, aluminum, silicon.

______________________ – tin (host metal), copper, lead, antimony.

______________________ – iron (host metal), chromium with very small amounts of carbon, nickel, manganese & molybdenum.



CONCEPT: SOLID STATE STRUCTURAL FEATURES Solids are grouped into two broad categories based on the organization of their particles and shapes:

_______________________ solids.

• Tend to have well-established shapes because their particles occur in an organized pattern.

_______________________ solids.

• Tend to have poor-established shapes because their particles lack an overall organized pattern.

When examining the particles within a crystal you may observe them tightly packed in an organized pattern.

• The ____________________ point represents the area within the crystal that has identical surroundings all around.

• The ____________________ represents the smallest portion of the crystal that, if reproduced in all three directions, would give the crystal.



CONCEPT: THE SIMPLE CUBIC UNIT CELL

There are ______ crystal systems and ______ types of unit cells that naturally occur, but we will only focus on those that follow cubic lattice system.

The simple cubic unit cell is made of a cube with one atom at each corner.

• The edge length is twice the radius of the atoms so ____________________.

• Then unit cell does not contain 8 atoms, but actually only ___________ atom because

each corner atom is shared by eight other unit cells.

• The packing efficiency is equal to ___________________________.

• The coordination number is equal to _______________________.

Unit Cell Diagram

Lattice Diagram

Space Filling Unit Cell Diagram



CONCEPT: THE BODY-CENTERED CUBIC UNIT CELL

The body-centered cubic unit cell is made of a cube with one atom at each corner and one atom of the same kind in the center of the cube.

• The edge length is equal to _________________________ .



Unit Cell Diagram

Lattice Diagram




CONCEPT: THE FACE-CENTERED CUBIC UNIT CELL

The face-centered cubic unit cell is made of a cube with one atom at each corner and one atom of the same kind in the center of each cube face.

• The edge length is equal to _________________________.



Unit Cell Diagram

Lattice Diagram




PRACTICE: THE CUBIC UNIT CELL (CALCULATIONS 1) EXAMPLE 1: An element crystallizes in a face-centered cubic lattice and it possesses a density of 2.03 g/cm3. The edge of its unit cell is 4.11 x 10-8 cm. How many atoms are in each unit cell?

EXAMPLE 2: Based on Example 1, what is the volume of a unit cell?

EXAMPLE 3: Based on Example 1, what is the mass a unit cell?

EXAMPLE 4: Based on Example 1, calculate the approximate atomic mass of the element.



PRACTICE: THE CUBIC UNIT CELL (CALCULATIONS 2) EXAMPLE 1: KF has the same type of crystal structure as NaCl. The unit cell of KF has an edge length of 5.39 angstroms. Find the density of KF.

EXAMPLE 2: Which one of the following is not a general property of ionic solids?

a) Hard and brittle b) Good electrical conductors in the solid state c) Relatively high melting points d) Strongest interparticle attractions are electrostatic e) Positions of ions define the unit cell (lattice)

EXAMPLE 3: Lead crystallizes in a face-centered cubic structure. What is the edge length of the unit cell if the atomic radius of gold is 180 pm?

a) 185 pm

b) 288 pm

c) 360 pm

d) 509 pm



PRACTICE: THE CUBIC UNIT CELL (CALCULATIONS 3)

EXAMPLE 1: Chromium metal crystallizes in a body-centered cubic structure with a unit cell edge length of 2.89 angstroms. The radius of a chromium atom is __________ angstroms.

a) 0.91

b) 3.90

c) 2.25

d) 1.25

e) 1.57

EXAMPLE 2: A solid has a very high melting point, great hardness, and poor electrical conduction. This is a(n) __________ solid. Example: Rubies

a) covalent network

b) metallic and covalent network

c) ionic

d) metallic

e) molecular

EXAMPLE 3: Determine the radius of an Ag atom (in pm) if the density of silver is 10.5 g/cm3. Silver crystallizes in a face

centered cubic structure with an edge length of 4r 2 .

a) 144 pm

b) 186 pm

c) 83 pm

d) 303 pm

e) 127 pm



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