Section 3.1 SUBSTANCE: matter that has a uniform composition.

Mixture A combination of two or more pure substances that are not chemically combined. Substances held together by physical forces, not chemical No chemical change takes place Each item retains its properties in the mixture They can be separated physically Chem4kids.com

Classifying Mixtures Mixtures can be classified as heterogeneous mixtures or as homogeneous mixtures.

Classifying Mixtures Heterogeneous Mixture A mixture that does not blend smoothly throughout Example: Sand mixed with water, soup Homogeneous Mixture A mixture that has constant composition throughout Homogeneous mixture = SOLUTION Example: Salt dissolved in water, Gatorade

Check Homogeneous or heterogeneous mixture? a) vinegar b) iron filings in sand c) chicken noodle soup d) muddy water a) Homogeneous b) Heterogeneous c) Heterogeneous d) Heterogeneous

Elements v. Compounds Matter can be classified as either ELEMENTS or COMPOUNDS

Element – A pure substance that cannot be separated into a simpler substance by physical or chemical means.

Compound Combination of two or more different elements that are combined chemically. Made of elements in a specific ratio that is always the same Has a chemical formula Can only be separated by chemical means, not physically

Elements v. Compounds - Practice Element or Compound? Neon (Ne) Water (H2O) Salt (NaCl) Carbon Dioxide (CO2) Sulfur (S) Element Compound Element

Classification of Matter Matter changes changes Sketch this in your notes. Use the figure on p. 71.

Classification of Matter Matter Mixtures Heterogeneous mixtures Homogeneous mixtures Pure Substances ElementsCompounds Physical changes Chemical changes

The diagram shows mixtures of elements and compounds. Each circle represents an atom of an element. Match the pictures A to E to the following questions. (a) Which picture represents a mixture of two compounds? ____ (b) Which picture represents a pure compound? ____ (c) Which picture represents a pure element? ____ (d) Which picture could represent pure water? ____ (e) Which picture could represent something dissolved in water? ___

Classifying Mixtures - Solutions Heterogeneous Mixture Example: Soup Homogeneous Mixture - SOLUTIONS Only one phase (gas, liquid, solid) Gas in gas Gas in liquid Liquid in gas Liquid in liquid Solid in liquid Solid in solid