Transcript Solids - Weebly

Ch. 12
3 Most Common Phases of Matter
Crystal Structure
Crystal Structure
• Metals, salts, and most
minerals are made up of
crystals!
• In 1912 physicists used xrays to confirm that each
crystal is a 3D orderly
arrangement of atoms
– It took us quite awhile to
actually see it!
Max von Laue
• Discovered that a beam of X-rays directed upon a
crystal is diffracted, or separated, into a specific
pattern
• X-ray diffraction patterns on photographic film show
crystals to be neat, uniform lattices
Metals
• All metals contain a jumble
of many crystals, each
almost perfect, with the
same regular lattice
• These metal crystals can be
seen when a metal surface
is etched, or cleaned with
acid
Amorphous
Amorphous Solids
• Noncrystalline solids are amorphous
– Atoms and molecules in a solid are distributed
randomly
• Rubber, glass, and plastic all lack an orderly,
repetitive arrangement at a molecular level
– You can tell because rubber is elastic, glass flows
when stressed
4 Principal Types of Bonding in Solids
Atoms are tied together by electrical bonding
forces. For solids this includes:
• Ionic
• Covalent
• Metallic
• Van der Waals’
Which of these is weakest?
Mini Quiz
1) How does the arrangement of atoms in a
crystalline substance differ from that in a
noncrystalline substance?
2) What evidence can you cite for the
microscopic crystal nature of certain solids?
3) For macroscopic crystal nature of certain
solids?
Density
• Is iron heavier than wood?
Density
• The masses of the atoms and the spacing
between them determine the density of
materials
– A measure of the compactness of matter, OR
– how much mass occupies a given space OR
– the amount of mass per unit volume
Density Formula
Density
• The density is a property of a material
• Therefore it doesn’t matter how much of the material you
have
• Density of a material depends upon the
masses of the individual atoms that make it up
and the spacing between those atoms
Units for Density
• g/cm3
– 1cm3 = 1mL
• When we do weight density then we use N/m3
– because a 1kg body has a weight of 9.8N, weight
density is numerically 9.8 x mass density
Mini Quiz
1) Is iron or wood heavier? Explain!
2) Density is a ______________ of a material.
This means it doesn’t depend on how much
of the material you have.
3) What is one of the correct units we might use
for density?
Elasticity
• When an object is subjected to external
forces, it undergoes change in size, or shape,
or both.
• The change depends on the arrangement and
bonding of the atoms in the material
– Example: A spring can be stretched or compressed
by an external force
Elasticity
• A weight hanging on a spring stretches the
spring
• Additional weight stretches the spring
___________
Inches and pounds… yuck
who even uses those?
Elasticity
• If the weights are removed, the spring returns
to its original length
• We say that the spring is elastic
Examples of Elasticity
• When a batter hits a
baseball, the bat
temporarily changes the
ball’s shape
• An archer, about to shoot
an arrow, first bends the
bow, which springs back
to its original shape when
the arrow is released.