1. Chapter 15: Composition of Matter

2. Pure Substances
Materials are made of either a mixture of substances, or a pure substance
What is a Pure Substance?
A type of matter with a fixed composition
Ex: Helium, water, salt
There are two types of substances:
1. Elements
2. Compounds

3. Substances All substances are built from atoms
Remember what an atom is……
The smallest particle of an element that still retains the properties of the element
What is in the nucleus of an atom?
Protons (p+) and neutrons (n0)
What is surrounding the nucleus?
Electrons (e-)

4. Elements What is an Element? A substance with atoms that are all alike
Ex: Helium in a balloon, Mercury in a thermometer
See page 451
Graphite in your pencil point is made up of carbon atoms
Copper covering of the penny is made of copper atoms

5. Compounds What is a Compound?
A substance formed from two or more elements combined in a fixed proportion
Ex: Water, H2O (2 hydrogen's and 1 oxygen atom combined)
Ex: The picture shows the metal sodium and chlorine as a gas
They combine to make salt, (NaCl) 1 sodium and 1 chlorine atom
Compounds look different from the elements they are made up of

6. Questions How are elements and compounds related?
Compounds contain two or more different elements
Is Cl2 an element or a compound?
Element – it has 2 atoms that are alike (2 chlorine atoms)
Is CO2 an element or a compound?
Compound – it has two different elements (1 carbon atom and 2 oxygen atoms)

7. Mixtures What is a Mixture? Two types of mixtures: 1. Heterogeneous
A material made up of two or more substances that can be easily separated by physical means
Two types of mixtures:
1. Heterogeneous
2. Homogeneous

8. What is Matter?
Matter is any substance that has mass and takes up space

9. What is a heterogeneous mixture?
A mixture in which different materials are unevenly distributed and can be easily distinguished
Ex: Pizza, soup, fabric blends

10. What is a homogeneous mixture?
A mixture that contains two or more substances blended evenly throughout
Ex: Vinegar (acetic acid mixed with water), soda

12. What is a solution?
A homogeneous mixture of one substance dissolved in another
This is just another name for a homogeneous mixture
Very small particles don’t settle to the bottom of the container
Ex: Soda, Kool-aid
Remain constantly and uniformly mixed

13. What are Colloids?
A type of mixture with particles that are larger than those in a solution, but not heavy enough to settle
Ex: Milk, Paint, fog, smoke

14. How to tell if it is a solution or a Colloid
Done by passing light through the substance

15. How to tell if it is a solution or a Colloid
Tyndall Effect – The scattering of light by colloidal particles
Large particles reflect light, smaller particles don’t

16. What is a suspension?
A heterogeneous mixture containing a liquid in which visible particles settle
Ex: sand in water, dust in air
If you don’t want to wait until the sand settles out you can use a filter to filter the sand out

17. This table is on page 456 in your book

18. 15.2: Properties of Matter What is a Physical Property?
Any characteristic of a material that you can observe or measure without changing its identity
Ex: Color, shape, size, boiling point, magnetism, flow of a liquid
Describe the physical properties of the tennis ball

19. What is a physical change?
A change in size, shape, or state of matter
Might involve energy changes, but……
Identity of the element or compound does not change
Examples: breaking, bending, stretching, heating
When heating iron it first glows red, then if it is heated to a higher temp. it will turn white
These energy changes are physical changes b/c it is still iron

20. List three examples of physical changes
Boiling water
Ice cube melting
Melting cheese on a pizza
Chewing gum

21. Separation using Physical Changes
What is Distillation?
Separating substances by evaporating, then recondensing its vapor
Distillation can easily separate liquids from solids dissolved in them
The liquid is heated until it vaporizes and moves up the column
Then, as it touches the water-cooled surface of the condenser, it becomes liquid again

23. Chemical Properties and Changes
What is a Chemical Property?
A characteristic of a substance that indicates whether it can undergo a certain chemical change
Ex: Flammability, exposure to light

24. Detecting a Chemical Change
What is a Chemical Change?
Change of one substance to another
The identity of the substance changes
Ex: Burning, rusting, food rotting

25. Detecting a Chemical Change
Signs of a chemical change:
Smell
Rapid release of energy
Heat
Light
Sound
Bubble formation

26. Physical or Chemical Change Quiz

27. Physical Weathering
Particles break off of rock, but still have the same identity
Rocks splitting
Water gets in cracks, freezes, and expands
Streams carve out canyons

28. Chemical Weathering The chemical identity of rock changes
Limestone dissolves from slightly acidic water
Calcium carbonate becomes calcium hydrogen carbonate
Caves are carved out by this process

29. Conservation of Mass What is the Law of Conservation of Mass?
Matter is neither created nor destroyed during a chemical reaction
Mass of all substances before reaction equal mass of all substances after reaction

30. Conservation Of Mass Calculations
If 20g of iron reacts with 3g of oxygen, how much iron oxide will be produced?
Mass of Fe = 20 g
Mass of O = 3 g
Mass of Fe2O3 = ?
20 g + 3 g = 23 g

31. Conservation of Mass Example: Fire
A pile of ashes is much smaller than original log
However, some of the mass of the log went into smoke and other gases

32. Conservation of Mass Demo
Citric acid plus baking soda
Citrate + Sodium Hydrogen Carbonate 
Carbon Dioxide + Sodium Citrate + Water

33. Conservation of Mass Demo
Was this a physical or chemical change?
What evidence suggests this type of change took place?
If this was not done in a plastic bag, would the mass before equal the mass after the reaction?