1. 18.1 – Composition of Matter
Chapter 18
18.1 – Composition of Matter

2. Objectives Define pure substances and mixtures.
Identify elements and compounds.
Compare and contrast solutions, colloids, and suspensions.

3. Pure Substances Type of matter with a fixed composition
Can be element or compound
Element = pure substance in which all atoms have the same identity
90 elements found on Earth
20+ have been made in labs
Most are unstable and exist for a short period of time

5. Pure substance
Compounds = when 2 or more different elements combine in a fixed proportion
Water, Table Salt (NaCl)
Molecules = particle consisting of 2 or more atoms bound together

6. Mixtures
Material made up of 2 or more substances that can be easily separated by physical means
Heterogeneous mixtures = mixture in which different materials can be easily distinguished
Granite, Concrete, Pasta Salad, Clothing

7. Mixtures
Homogeneous mixture = 2 or more substances blended evenly throughout
Soft drinks, Pudding, Vinegar
Solution = particles so small that they cannot be seen with microscope and will never settle to the bottom of their container

9. Colloids
Mixture with particles that are larger than those in solutions but not heavy enough to settle out
Greek word for “glue”
Examples: Milk, Gelatin

10. Detecting Colloids Pass light beams through
Solutions = no light comes through
Colloids = light readily passes through
Tyndall Effect = scattering of light by colloidal particles

11. Suspensions
Heterogeneous mixture containing liquid in which particles settle
Example: Pond Water

12. In-Class Assignment/Homework
18.1 WKT
Homework = 18.1 Directed Reading WKT