1. Chapter 2 Properties of Matter

2. 2.1 Classifying Matter

3. Pure Substances
Pure Substances: matter that always has exactly the same composition
Every sample has the same properties because a pure substance has a fixed, uniform composition
Ex: table salt & gold

4. Pure Substances There are 2 categories of Pure Substances: Elements
Compounds

5. Elements
Element: a substance that cannot be broken down into simpler substances
Elements contain only one type of atom
Ex: Copper wire is made up of only copper atoms
More examples: carbon, gold, aluminum, iodine (see the Periodic Table)

6. Elements Elements are represented with symbols
Ex: C = carbon, I = iodine, Au = gold
Au ????? Well the Latin name for gold is aurum

7. Compounds
Compound: a substance that is made up from 2 or more atoms chemically bonded together
A compound can be broken down, but only by chemical means
Ex: NaCl = Sodium chloride or table salt

8. Elements
The properties of the elements that make up a compound are different than the compound that they form
Ex: H2O water
What are the properties of H & O when they are not bonded together?

9. Question
Question: Can water have any other proportion than 2 hydrogen and 1 oxygen?
Can H3O be water?

10. Answer
Of course not!! That’s because the elements that make up a compound are joined in a fixed proportion!

11. Mixtures
Now to the other side of the Map…

12. Mixtures
Mixture: contains parts that are combined but the parts can be put together in varying amounts (it is NOT a fixed proportion)
And…
The parts retain their individual properties
Ex: Salsa

13. Types of Mixtures There are 2 kinds of mixtures:
Heterogeneous
Homogeneous
Mixtures are classified by how well mixed they are

14. Heterogeneous Mixtures
Heterogeneous Mixture: has parts that are noticeably different from one another
Ex: Salsa and beach sand
Ex: Suspensions such a sand and water mixed together
It will separate into layers over time
A filter could be used to separate because of larger particles (Filtration)

15. Homogeneous Mixtures
Homogeneous Mixture: is so well mixed that it is difficult to distinguish the parts
In other words, it looks like a pure substance or like it is all the same stuff
Ex: a salt water mixture

16. Homogeneous Mixtures Types of Homogeneous mixtures
Solutions: substances dissolved together (smallest sized particles)
Ex: sugar water, salt water, pool water
Colloids: intermediate sized particles that are suspended between small sized particles that do not separate
Ex: milk & fog

17. 2.2 Physical Properties

18. Physical Property
Physical Property: any characteristic of a material that can be observed or measured without changing the composition of the substances in the material

19. Examples of Physical Properties
Our textbook describes 5 physical properties, however there are many more!
Viscosity
Conductivity
Malleability
Melting Point
Boiling Point

20. Viscosity
Viscosity: tendency of a liquid to keep from flowing – its resistance to flowing
The slower a substance moves, the higher its viscosity
Viscosity decreases when it is heated
Example: Which has the higher viscosity: water or honey?

21. Conductivity Conductivity: material’s ability to allow heat to flow
Which spoon should you choose for stirring a pot of soup heating on the stove – a metal spoon or a wooden spoon? Why?

22. Conductivity Conductors have HIGH conductivity
Examples?
Insulators have LOW conductivity
Which items are conductors? Insulators?

23. Malleability
Malleability: ability of a solid to be hammered without shattering
What types of solids would be considered malleable?
What types of solids are brittle (the opposite of malleable)?

24. Hardness
One way to compare the hardness of two materials is to see which of the materials can scratch the other.
Compare the hardness of various materials

25. Mohs Hardness Scale

26. Melting & Boiling Points
Melting Point: temperature which a substance changes from a solid to liquid
For water, this occurs at what temperature in Celsius?
Boiling Point: temperature which a substance boils (liquid to a gas)

27. Density Density is the ratio of the mass of a substance to its volume.
Calculated by dividing the mass by the volume
Density = Mass / Volume
Used to test the purity of a substance

29. Using Physical Properties
Physical properties can help us do the following:
Identify unknown materials
Choose appropriate materials
Would you ever make shoelaces out of wood??!!

30. Separating Mixtures Some properties can be used to separate mixtures:
Filtration
Distillation

31. Filtration
Filtration: physical process that separates materials based on the size of their particles
Examples: making coffee & tea, separating sand from water

32. Distillation
How can you separate the parts of a solution when all particles are small enough to pass through a filter?
Distillation: physical process that separates the substances in a solution based on their boiling points.
Example: distillation of sea water to create fresh water

33. Distillation

34. Physical Changes
Physical Change: when some of the properties of a material change, but the substances in the material remain the same
Examples: braiding hair, cutting paper, melting butter, boiling water

35. Reversible Physical Changes
Some physical changes can be reversed.
Examples reversible physical changes:
Examples of non-reversible physical changes:

36. 2.3 Chemical Properties

37. Observing Chemical Properties
Chemical properties can be observed only when the substances in a sample of matter are changing into different substances!
Two examples include:
Flammability
Reactivity

38. Flammability
Flammability: a material’s ability to burn in the presence of oxygen
Examples of flammable objects: paper & gasoline

39. Reactivity
Reactivity: how readily a substance combines chemically with other substances
Example: Rust – reaction that occurs when oxygen reacts with iron and water

40. Reactivity
QUESTION: Nitrogen & oxygen are the two most abundant gases in the atmosphere. Is it possible that both gases are highly reactive? Explain your answer…

41. Chemical Changes
Chemical Change: occurs when a substance reacts and forms one or more NEW substances
Examples: baking a cake, leaves changing colors in the fall, & food digested in your stomach

42. Recognizing a Chemical Change
There are 3 common clues that a chemical change has taken place:
Change in color
Production of a gas
Formation of a precipitate

43. Change in Color EXAMPLES:
Over time a shiny silver bracelet that is exposed to air will darken
As a match burns, it shrivels up and turns black
A new copper roof will turn green with time
All of these are clues that a chemical change has occurred

44. Production of a Gas EXAMPLES:
Mixing vinegar and baking soda  bubbles of carbon dioxide (CO2)
Baking powder used when baking  as the cake bakes, bubbles of CO2 expand and cause the cake to rise
Click HERE for video

45. Formation of a Precipitate
Precipitate: any solid that forms and separates from a liquid mixture
If you add lemon juice or vinegar to milk, small bits of white solid will separate from the liquid
When acid is added to milk, proteins in the milk undergo a chemical change that alters their structure, causing them to stick together in clumps

46. Precipitates

47. Be CAREFUL With the Chemical Change Clues!!!
Do the coils on a hot stove top mean a chemical change has occurred?
When water boils on a stove, what are the bubbles that rise to the surface?

48. Chemical or Physical
Before you decide if it was a chemical or physical change – ask yourself this question:
Are different substances present after the change takes place…if not, then the change is physical, not chemical.
When matter undergoes a chemical change, the composition of the matter changes! When matter undergoes a physical change, the composition of the matter remains the same!

49. Chemical Change Video Review