1. Matter—Properties and Changes
Chapter 3
Matter—Properties and Changes

2. Classifying Matter
The word composition comes from a Latin word meaning “a putting together,” or the combining of parts into a whole.
Based on their compositions, materials can be divided into pure substances and mixtures.

3. Pure Substances
Matter that always has exactly the same composition is classified as a pure substance, or simply a substance.
Table salt and table sugar are two examples of pure substances.
Every pinch of salt tastes equally salty. Every spoonful of sugar tastes equally sweet.  
Every sample of a given substance has the same properties because a substance has a fixed, uniform composition.
Substances can be classified into two categories—elements and compounds.

4. Examples of Physical Properties
A physical property is any characteristic of a material that can be observed or measured without changing the composition of the substances in the material.  
Density, color, odor, taste, hardness, melting point, and boiling point are examples of physical properties.

5. Extensive and Intensive Properties
Extensive properties are properties that are dependent upon the amount of substance present. For example, mass, length, volume.
Intensive properties are properties that are not dependent (independent) of the amount of substance present. For example, density.

6. Using Properties to Identify Materials
The steps used to identify a material are similar to the steps used to test for purity.
The first step is to decide which properties to test.
The second step is to do tests on a sample of the unknown.
The final step is to compare the results with the data reported for known materials.

7. Chemical Properties
A chemical property is any ability to produce a change in the composition of matter.  
Chemical properties can be observed only when the substances in a sample of matter are changing into different substances.
Flammability and reactivity are two examples of chemical properties.

8. States of Matter
Materials can be classified as solids, liquids or gases based on whether their shapes and volumes are definite or variable.
Shape and volume are clues to how the particles in the material are arranged.

9. Solids
Solids are the state of matter in which the material has a definite shape and definite volume.
Definite means that the volume and shape of the object does not change as you move it.
But that does not mean that the shape and volume will never change.
In solids, the particles are packed close together in a regular pattern and very orderly arranged on the atomic level.

10. Liquids
Liquid is the state of matter that has a definite volume but no definite shape.
Liquids take the shape of their container and can be poured from one container to another.
The atoms in liquids are still closely packed but are less orderly arranged.

11. Gases
Gases are the state of matter that has no definite shape and no definite volume.
A gas takes the shape and volume of its container.
Gas particles do not have an order arrangement in containers.
They are at random locations throughout the container.
Because of the space among particles in a gas, gases can be compressed into metal containers.

12. Vapors The words gas and vapor do not mean the same thing.
Gas refers to a substance that is naturally in the gaseous state at room temperature. For example, methane.
Vapor refers to the gaseous state of a substance that is a solid or liquid at room temperature. For example, steam.

13. Recognizing Physical Changes
A physical change occurs when some of the properties of a material change, but the substances in the material remain the same.
For example, if you slowly heat butter in a pan, it changes from a solid to a liquid, but the substances in the butter do not change.
Heating, crumpling a piece of paper and slicing a tomato are all physical changes because they change the size and shape of a material, but not its composition.

14. Chemical Changes
When one or more substance changes into new substances it is called a chemical change, which is commonly referred to as a chemical reaction.
The new substances in the reactions have different compositions and different properties from the substances present before the reaction occurs.

15. Recognizing Chemical Changes
The color change in a banana peel is caused by chemical changes that are taking place in the cells of the banana.
A chemical change occurs when a substance reacts and forms one or more new substances.
Chemical changes occur when a cake bakes in an oven, leaves on trees change color, and food is digested in your stomach.

16. Chemical Changes
How can you recognize a chemical change? You have to look for clues. For example, when food spoils, it often gives off an unpleasant odor.  
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.

17. Massreactants=Massproducts
Conservation of Mass
This law says that the mass before and after a chemical reaction remains the same.
It says that mass is neither created or destroyed in a chemical reaction.
Massreactants=Massproducts

18. Mixtures
Mixtures tend to retain some of the properties of their individual substances.
The properties of a mixture can vary because the composition of a mixture is not fixed.
There are two types of mixtures: Heterogeneous and Homogeneous.

19. Heterogeneous Mixtures
Heterogeneous comes from the Greek words hetero and genus, meaning “different” and “kind.” In a heterogeneous mixture, the parts of the mixture are noticeably different from one another.
Sand is an example of a heterogeneous mixture.

20. Homogeneous Mixtures
In a homogeneous mixture, the substances are so evenly distributed that it is difficult to distinguish one substance in the mixture from another.
A homogeneous mixture appears to contain only one substance.
A serving spoon made of stainless steel represents a homogeneous mixture of iron, chromium, and nickel.
The water in a swimming pool is also an example of a homogeneous mixture.

21. Solutions, Suspensions, and Colloids
It isn't always easy to tell a homogeneous mixture from a heterogeneous mixture.
You may need to observe the properties of a mixture before you decide.
The size of the particles in a mixture has an effect on the properties of the mixture.  
Based on the size of its largest particles, a mixture can be classified as a solution, a suspension, or a colloid.

22. Using Properties to Separate Mixtures
Some properties can be used to separate mixtures.
Filtration, distillation, crystallization and chromatography are common separation methods.

23. Pure Substances
Matter that always has exactly the same composition is classified as a pure substance, or simply a substance.
Table salt and table sugar are two examples of pure substances.
Every pinch of salt tastes equally salty. Every spoonful of sugar tastes equally sweet.  
Every sample of a given substance has the same properties because a substance has a fixed, uniform composition.
Substances can be classified into two categories—elements and compounds.

24. Elements
Although there are millions of known substances, there are only about 100 elements.
An element is a substance that cannot be broken down into simpler 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 type of atom.

25. Examples of Elements
 At room temperature (20°C, or 68°F), most elements are solids, including the elements aluminum and carbon.
Some elements are gases at room temperature. The elements oxygen and nitrogen are the main gases in the air you breathe.
Only two elements are liquids at room temperature, bromine and mercury, both of which are extremely poisonous.

26. Symbols for Elements
Each element has a symbol that consists of either one or two letters. The first letter is always capitalized. If there is a second letter, it is not capitalized.
For most symbols it is easy to see what they will be, but some come from different languages, like Gold (Au) and silver (Ag).

27. Periodic Table
As new elements were being discovered they were organized in a periodic table.
All elements in the world can be found on the periodic table.

28. Compounds
A compound is a substance that is made from two or more simpler substances and can be broken down into those simpler substances.
The simpler substances are either elements or other compounds.
The properties of a compound differ from those of the substances from which it is made.
A compound always contains two or more elements joined in a fixed proportion.

29. Law of Definite Proportions
The law of definite proportions says that regardless of the amount, a compound is always composed of the same elements in the same proportion by mass.
For example, sucrose. In g, there are always 8.44 g of carbon, 1.30 g of hydrogen and g of oxygen.
The proportion is obtained by calculating the percent by mass.

30. Percent by Mass
Percent by mass of found of the elements in a compound by the following formula:
Percent by mass = mass of element x %
mass of compound

31. Law of Multiple Proportions
This law states that when different compounds are formed by a combination of the same elements, different mass one element combine with the same relative mass of the other elements in a ratio of small whole numbers.
See page 76 in your textbook.