18.1 – Composition of Matter Chapter 18 18.1 – Composition of Matter

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

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

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

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

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

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

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

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

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