11 Terminology Element – group of atoms with the same number of protons. Compound – chemical substance formed from 2 or more elements and which has a definite chemical formula. Compounds do not have to formed from molecules since compounds can be crystal structures such as table salt. Mixture – substance with components that have not combined chemically. Chemical Substance - an element, compound, or mixture. Molecule – smallest particle of chemical substance that has the same composition and chemical properties, e.g. water molecule.

12 Solids Crystal Structure Crystal Power? Density Elasticity Tension and Compression Arches Scaling

Crystal Structure solids with a regularly repeating pattern are crystals Examples: Graphite NaCl hexagonal cubic

X-Ray Crystallography X-Rays are used to determine the structure of crystalline solids

Density Density = mass/volume depends on chemical type and structure water 1.0 grams/cm 3 ice 0.9 grams/cm 3 copper 8.9 grams/cm 3 lead 11.9 grams/cm 3 gold 19.3 grams/cm 3

Elasticity - ability to regain shape elastic material – perfectly regains shape inelastic material – incompletely regains shape elastic limit – force in which an elastic material becomes inelastic

Hooke’s Law Elastic Force ~ amount of stretch or compression F ~  x Example: many springs obey Hooke’s Law within their elastic limit.

Hooke’s Law

Longer objects are easier to stretch. Thicker objects are harder to stretch.

Tension, Compression, and Bending

Strength and Shape

Scaling mass ~ size 3 strength ~ size 2 how does this affect animals and structures when changing their size?

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