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• Define atom, element, and compound.
• Recognize the relative sizes of atoms, compounds, and crystal
grains.
• State the four properties that distinguish metals from nonmetals.
• Distinguish between the three major crystal structures found in
metals: face-centered cubic, body-centered cubic, and hexagonal
close-packed.
Learning Objectives
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• Name metals in each of the three major metal crystal structures
(face-centered cubic, body-centered cubic, and hexagonal close-
packed).
• Understand how metals can deform at the atomic level, while
minerals and ceramic materials cannot deform without fracturing.
Learning Objectives
5. Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.
• Recognize that the conversion of metal ore to metal and the
oxidation of metal to form metal oxide use the same chemical
reaction, but in opposite directions.
• Distinguish between a solution and a mixture, as applied to liquids
and solid metals.
• Understand and identify grains in the structure of a metal alloy.
• Understand how the term phase describes solutions in metals.
Learning Objectives
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• Metals are defined by macroscopic
properties.
• Properties observed and measured by eye
• SI units measured in meters (m) and
millimeters (mm)
• Atoms are much smaller and measured in
smaller units.
• Micrometer (μm) = 1/1000 mm
• Nanometer (nm) = 1/1000 μm
Measurement Scales
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• Micrometer (my-crom-eter)
• Tool for precise measurements to within
1/1000 inch
• Micrometer (mike-row-meter), or micron
• Unit of measurement, one millionth of a
meter
• Symbol is μm
Micrometer and Micrometer (μm)
L.S. Starrett Company
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• Stereo microscope shows magnified details of
small objects.
• Up to 80X magnification
• Useful for examining small details of parts
Observing Millimeter (mm) to
Micrometer (μm) Scale
Unitron, Inc.
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• Scanning electron microscope (SEM)
• Shoots beam of electrons at object instead
of light beam
• Increases magnification into nanoscale
• Academic and corporate research
laboratories use SEMs to analyze fracture
surfaces.
Higher-Magnification Examinations
Ben Church, Advanced Analysis Facility, UW-Milwaukee
10. Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.
• Universe is made of elements.
• Atom is smallest unit of element that has properties of that element.
• Atoms are made of protons, neutrons, and electrons.
Atomic Elements
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• Nucleus (center) contains positive
protons and any neutral neutrons.
• Nucleus is surrounded by cloud of
orbiting, negatively-charged
electrons.
• Only outermost electrons influence
behavior of metals.
Atomic Element Structure
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• Chromium metal is commonly used with many steel types.
• Welding and plating can cause chemical reaction resulting in
hexavalent chromium.
• Hexavalent chromium forms when all six outer electrons are
involved.
• People working nearby must be protected from these toxic fumes.
Hexavalent Chromium
Safety Note
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• Contains 92 naturally occurring
elements
• Each element has atomic
symbol (such as H for
hydrogen).
• Each element has atomic
number (number of protons in
nucleus).
Periodic Table of the Elements
Goodheart-Willcox Publisher
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• When two or more atoms come close to one another they may
combine.
• This unique substance is called a compound.
• Molecule is smallest particle of compound that still has
characteristics of that compound.
Compounds
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• How electrons are shared between atoms determines many
properties of a substance and ratios of atoms in a molecule.
• Force developed between two atoms by sharing electrons is known
as covalent bond.
Compounds with Covalent Bonds
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16. Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.
• Ionic bonds are found in compounds that bond metals to nonmetals.
• Ionic bonds form between two atoms when one or more electrons
from one atom completely transfer to another atom.
Ionic Bonds between Atoms
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• Metals do not form fixed bonding ratios
between atoms.
• Electrons move between atomic nuclei,
associating equally with all nuclei.
• Voltage applied to metal creates electric
current.
• Current can be measured directly with
ammeter.
Metallic Bond
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• Properties of compounds are different
from properties of each element alone.
• Aluminum conducts electricity, but
aluminum oxide does not.
• Nonmetals and compounds with
nonmetals have certain properties in
common.
• Brittle fracture
• Poor electrical conductivity
Properties Depend on Bonding
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• Electrical conductivity: ability to conduct electricity
• Thermal conductivity: ability to conduct heat
• Formability: ability to deform and change shape without breaking
• Reflectivity: shininess, or ability to reflect light
Four Defining Properties of Metals
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• Metal atoms collected together in stable
positions line up in regular, orderly
arrangement.
• This regular array is called a space
lattice.
• Unit cell is smallest volume that
encloses complete atomic structure.
• Three common unit cells found in metals
Crystal Structures
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• Room-temperature iron has a bcc unit cell.
• Cube shaped, with one atom at each corner
and one atom at exact center of cube
• Metals can be hit and will dent rather than
break.
• Dent occurs as atoms slide past one another.
• Sliding occurs most easily in certain directions
in unit cells.
Body-Centered Cubic (BCC)
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• Unit cell for room-temperature aluminum has
fcc structure.
• Cube shaped, with one atom in each corner
and one atom at center of each face of cube
• Fcc structure has more directions for atoms to
slide past one another than bcc structure.
• Metals with fcc atomic structures are more
formable than those with other crystal
structures.
Face-Centered Cubic (FCC)
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• Solid magnesium has hcp structure.
• Hcp unit cell consists of three layers of
hexagonal planes of atoms.
• Metals with hcp structures are less formable
than those with bcc or fcc structures.
Hexagonal Close-Packed (HCP)
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• Metal atoms are typically 0.28 nm apart.
• One atom must slide past a million other
atoms (106 atoms) before it moves 1/4 mm.
• Metal parts are not single crystals.
• They consist of many small individual
crystals called grains.
Deformation
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• Grains have different orientation where they meet.
• If etched with acid, grain boundaries react faster, revealing
boundary.
• Atoms slide slightly differently within grains and along grain
boundaries.
• This changes the surface smoothness.
Grain Boundary
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• In single crystals, plains of atoms slide past
other plains of atoms along slip planes.
• Atoms at grain boundaries are not clearly
aligned with either crystal.
• Allows for easier deformation by sliding
atoms along slip planes and grain
boundaries
Slip in Metals
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• Some reactions occur naturally in metals.
• Some reactions are purposefully used to obtain certain properties.
• Chemical reduction of metal ore changes it into metal.
Chemical Reactions in Production and
Use of Metals
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• Metal oxides are reduced to metals.
• Another element or compound oxidizes at the same time.
• Example: reduction of iron oxide
• Iron oxide is reduced to iron metal.
• Carbon is oxidized to carbon monoxide.
Reduction of Metal Ores to Metal
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• Oxygen dissolved in titanium metal can form titanium oxide inside
titanium.
• These particles degrade properties.
• When welding titanium, protective gas is used to prevent this.
• Sulfur in iron reacts to form iron sulfide.
• This can melt and cause steel to be hot-short at high temperatures.
• It tears along grain boundaries during forming processes.
• Steel is processed to keep levels of sulfur lower.
Compounds Formed in Bulk Metals
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• Mixture: combination of two or more substances that remain
unchanged individually and can be easily separated again
• Solution: combination of two or more substances in which one or
more substances is completely dissolved in another
• Phase: any region of a material with properties that are constant or
changing slowly and have one particular crystal structure
Mixtures, Solutions, and Phases
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• A mixture has two or more phases.
• Sugar added to cup of tap water (without stirring) forms mixture of
two phases.
• Sugar grains and water
• A solution has one phase.
• When heated, sugar goes into solution with water.
• Result is one phase, with no visible sugar.
Mixtures and Solutions: Sugar and Water
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• Metals at high temperatures may form
solutions and mixtures.
• Most alloys contain multiple phases at
room temperature.
• To see phases in solid metals,
samples are cut, polished, and etched.
Phases in Metals
Iron Castings Society
