Solids 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 x-rays 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?
Depends how much of Each you have!
Iron is denser though
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 Quiz1) 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
___________Further
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.
