Pure Substances

1
Pure Substances

• An atom is the smallest particle of an element.
• An element has a fixed composition because it
  contains only one type of atom.
• No two elements contain the same atoms.
• They are listed on the Periodic Table of Elements

• Most elements (100) are solids at room
  temperature (20C).
• 11 are gasses.
• 2 are liquids.
• All elements are represented by symbols that are
  standard through all countries.

2
Compounds/Mixtures

• Compound is a substance that can be broken down
  into simpler substances. The simpler substance
  is either are either elements or other compounds.
• Ex. H20 ? H2 02
• A compound always contains two or more elements
  joined in a fixed proportion.

• Mixtures are a sample of compounds and elements
  that are not chemically bonded and vary in
  properties because the composition of the mixture
  are not fixed.
• Ex. Salsa and sand

3
Types of Mixtures

• Heterogeneous Mixture a type of mixture in
  which the parts of the mixture are noticeably
  different from one another.
• Ex. Sand

• Homogeneous Mixture a type of mixture in which
  the substances are so evenly distributed that it
  is difficult to distinguish one substance in the
  mixture from another.
• Ex. Stainless Steel

4
Based on the size of its particles, a mixture can
be classified as a solution, a suspension or a
colloid.

• Solution a mixture that forms when substances
  dissolve and form a homogenous mixture. The
  particles do not settle out.
• Ex. Tap water, windshield washer fluid
• Solvent most abundant substance in a solution.
• Solute the least abundant substance in a
  solution.

• Suspension a heterogeneous mixture that
  separates into layers after time.
• Ex. Dirt and water
• Colloid a mixture that contains particles
  larger than a solution and larger than a
  suspension.
• Ex. Milk, fog

5
Physical Properties a characteristic of a
material that can be observed or measured without
changing the composition of the material.

• Viscosity tendency of a liquid to keep from
  flowing. (Higher viscosity, slower the fluid
  moves.
• Conductivity A materials ability to allow heat
  to flow.
• Density mass/volume

• Malleability the ability of a solid to hammered
  into sheets.
• Hardness Based on if one object can scratch
  another.
• Melting and Boiling Points-
• M.P. Solid to Liquid
• B.P. Liquid to Gas

6

• Filtration a process to separate materials
  based on their size. Examples include coffee
  filters and a screen to find artifacts at a
  historical site.
• Distillation a process that separates
  substances in a solution by using their boiling
  points.

• A physical change occurs when some of the
  properties of a material change, but the
  substances in the material remain the same.

7
Chemical Properties an ability to produce a
change in the composition of matter.

• Flammability a materials ability to burn in the
  presence of oxygen.

• Reactivity the property that describes how
  readily a substance combines chemically with
  other substances.

8
Recognizing Chemical Change

• A chemical change occurs when a substance reacts
  and forms one or more new substances.
• There are three common types of evidence of a
  chemical change

• A change in color.
• Production of gas.
• Formation of a Precipitate.
• A precipitate is a solid that forms and separates
  from a liquid mixture.