Post on 05-Jan-2016
Section 1: Describing Matter
What kinds of properties are used to describe matter?What are elements, and how do they relate to compounds?What are the properties of a mixture?
1. Elements• The building blocks of all matter in the
universe• Cannot be broken down into any other
substances
Elements
1. Elements (continued)• There are about 100 different types of
elements (listed in periodic table)Examples:• O = • N =• H =• C =• Cu =• Al =
Oxygen
NitrogenHeliumCarbonCopperAluminum
1. Elements (continued)
• Each type of element has its own properties
Cl = Chlorine Cu = Copper Br = Bromine
1. Elements (continued)
• Atoms = basic particles from which all elements are made
• Different atom = different element• Aluminum - Chlorine• Sodium - Oxygen
So, if there are only about 100 or so elements (building blocks) how come there are so many different examples
of matter (stuff)?
2. Compounds• When 2 or more elements combine
chemically (bonded together)
+ = Element Element Compound
Sodium Chlorine Sodium Chloride (salt)
2. Compounds (continued)• Atoms of the different elements are in a fixed
ratio
• Written as chemical formulas (letters and numbers)
Examples:• Water = H2O
• Carbon dioxide = CO2
• Glucose = C6H12O6
2. Compounds (continued)• When ratios change, a different compound
results
– CO = carbon monoxide
– CO2 = carbon dioxide
2. Compounds (continued)• Compounds have different properties than
the individual elements that make them up
+ =Element Element Compound
Silver (Ag) Chlorine (Cl) Silver Chloride (AgCl)
Shiny, gray metal Yellow/green gas Solid white crystals
3. Mixtures
• Contain of 2 or more elements, compounds, or both in the same place
• The components are NOT combined chemically
3. Mixtures (continued)
• Easy to separate (magnets, filtering, evaporating)
• Example: saltwater (salt in water, but salt stays salt, water remains water)
3. Mixtures (continued)
• Each substance keeps its own properties (salt = white grains, water = clear liquid)
• Do not have to be in a fixed ratio (lots of salt or a little salt, its still saltwater)
3. Mixtures (continued)
• There are 2 Types of Mixtures:
1. Heterogeneous Mixtures- Different parts are visible- Examples: Salad
Soil Pencil
3. Mixtures (continued)
2. Homogeneous Mixtures- Evenly mixed, looks the same throughout- Examples: Saltwater
Air Brass
Practice Questions1. How are elements and compounds similar? How are they different?
1. Plants make a sugar compound with the formula C6H12O6. What elements make up this compound?
1. Look at the following chemical formulas: H2O2 and H2O. Do these formulas represent the same compound? Explain.
4. How does a heterogeneous mixture differ from a homogenous mixture?
1. Why is it correct to say that saltwater is a mixture?
2. Suppose you stir baking soda into water until the water looks clear throughout. How could you prove to someone that the clear material is a solution, not a compound?