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"To the dull mind all nature is leaden. To the illumined mind the whole world burns and sparkles with light." -- Ralph Waldo Emerson

CLASSIFICATION OF MATTER

COMPOSITION OF MATTER

Concept Pages:

Physical Science "Key Concepts" Home Page


Section Review questions
Chapter review questions
 

Substances

  • Can be elements or compounds.
 

Elements

  • Are made entirely of the same type of atom.
 

Compounds

  • Are made from more than one type of atom, i.e., from more than one element.
  • A particular compound will always be found to have exactly the same ratio of the elements that it is made of.

      •  

  •  Are frequently nothing like their constituent parts.
e.g.:
 
  • Sugar
  • Salt
 

Mixtures

  • Are made of different substances, compounds or elements or both.
  • The ratios of the constituent parts of a mixture may differ from one example to the next.
     

e.g.     - Salt water:

  • Can be slightly salty or very salty.
 

Heterogeneous   Mixtures

  • Are those where the different substances can easily be distinguished.

      • e.g.     • Concrete, granite
 

Solutions

  • A homogeneous mixture:

• In which all the substances are uniformly mixed throughout the liquid.

• And in which you can't see individual parts of the substances like in heterogeneous mixtures.
Colloids
  • Are heterogeneous mixtures in which the separate substances remain in solution.

• But are made of particles that are larger than in homogeneous mixtures.

• And therefore can scatter light, which homogeneous mixtures don't do.

 An effect called:

  • The Tyndall Effect
 

Suspensions
  • Are heterogeneous mixtures with liquid that have larger, visible particles that settle out:

• Like muddy water.

 
Comparing Solutions, Colloids, and Suspensions
Description Solutions Colloids Suspensions
Settle while standing NO NO YES
Can be separated using filter paper NO NO YES
Sizes of particles 0.1 - 1 nm 1 - 100 nm Greater than 100 nm
Scatter light NO YES YES
 

Technology: The Colloid Connection

Uses of Colloids
  • Purifying drinking water

A gel-like colloid can be formed that will cause harmful microorganisms to stick to it.

• Food: Gelatin

 
Problems from Colloids
  • Pollution can sometimes be a colloid solution in the air, like some soot.

• Coagulation can be caused, which forms larger particles that will form a suspension, which will, of course, settle out.

DESCRIBING   MATTER
Physical  Properties
  • Characteristics of substances that you can observe without changing those substances:

• Appearance

• Brittleness

• Color
 

Identification by Properties

  • You might identify a substance by noting the properties it exhibits:

 
Physical Changes
• Break something
• Freeze it
• Or melt it
 
  • You may change a physical property of the substance,
    but you have not changed its Essence.

The materials that it is made of are still the same substances.

•  It is a change in the size, shape, state.

Chemical Changes

• Burn something

• Let it rust

  • Changes one substance into another substance.

 

To change identity - Is to change the substance essentially.
Weathering
  • Break down into a smaller version of the same substance:
    • Physical
  • Or turn it into something else:
    • Chemical
Chemical  Properties
  • Characteristic of a substance indicating its tendency to undergo certain chemical changes:

        • Flammable

        • Combustible

        • Light sensitivity

         
Conservation of Mass
  • If something burns, what happens to the mass of the substance that was there before it burned??

 
The Law of Conservation of Mass says:
 

The mass of all substances present before a chemical change

= The mass of all the substances remaining after a chemical change.

 
In other words…
 

Matter is neither created nor destroyed during a chemical change.

Updated 10/14/07