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Chapter 2
Chapter 2 Terms
27
Science
8th Grade
02/25/2008

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Term
Pure Substance
Definition
Matter that always has exactly the same composition

~Every sample of a given substance has the same properties because a substance ahs a fixed, uniform composition.
Term
Element
Definition
A substance that cannot be broken down into simpler substances

~An element has a fixed composition because it contains one type of atom
Term
Atom
Definition
The smallest particle of an element
Term
Compound
Definition
A substance that is made from two or more simpler substances and can be broken down into those simpler substances.

~A compound always contains two or more elements joined in a fixed proportion
Term
Mixture
Definition
The properties of a mixture can vary because the composition of a mixture is not fixed
Term
heterogeneous Mixtures
Definition
Parts of the mixture are noticeably different from one another
Term
Homogeneous Mixtures
Definition
Substances are so evenly distributed that it is difficult to distinguish one substance in the mixture from another
Term
Solution
Definition
A homogeneous mixture formed when substances dissolve

~Do not separate into layers over time
~No substances in solution can be trapped by a filter
~Light does not scatter

*Particles in a solution are smallest
Term
Suspension
Definition
Heterogeneous mixture that separates into layers over time

~Can be separated by a filter
~Scatter light

*Bigger particles than solutions
Term
Colloids
Definition
Contains some particles that are intermediate in size between the small particles in a solution and the larger particles in a suspension.

~Do not separate into layers
~Cannot use a filter to separate
~Does scatter light
Term
Physical Property
Definition
Any characteristic of a material that can be observed or measured without changing the composition of the substances in the material.
Term
Viscosity
Definition
Resistance to flowing

~Decreases when heater
Term
Conductivity
Definition
A material's ability to allow heat to flow
Term
Malleability
Definition
The ability of a solid to be hammered with shattering

~Solids that shatter easily are brittle
Term
Hardness
Definition
A material's ability to scratch a softer substance
Term
Boiling point
Definition
The temperature at which a substance boils
Term
Melting Point
Definition
The temperature at which a substance changes from a solid to a liquid
Term
Density
Definition
The ratio of the mass of a substance to its volume
Term
**Using Physical Properties
Definition
Used to identify a material, to choose a material for a specific purpose, or to separate the substances in a mixture
Term
Filtration
Definition
The process that separates materials based on the size of their particles
Term
Distillation
Definition
The process that separates the substances in a solution based on their boiling points
Term
Physical Changes
Definition
Occurs when some of the properties of a material change, but the substances in the material remain the same.

~Some Physical Changes can be reversed, some cannot
Term
Chemical Property
Definition
Any ability to produce change in the composition of matter. Chemical properties can be observed only when the substances in a sample of matter are changing in to different substances.
Term
Flammability
Definition
A material's ability to burn in the presence of oxygen
Term
Reactivity
Definition
How readily a substance combines chemically with other substances
Term
Chemical Changes
Definition
Occurs when a substance reacts and forms one or more new substances.

~Three common types of evidence for a chemical change are a change in color, the production of a gas, and the formation of a precipitate.
Term
Precipitate
Definition
Any solid that forms and separates from a liquid mixture
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