1. Elements, Compounds, & Mixtures Objectives:  1. Explain the difference between an element and a compound.  2. Compare heterogeneous and homogeneous mixtures.  3. Describe several techniques to separate mixtures. Key Terms:  Element, compound, pure substance, mixture, heterogeneous mixture, homogeneous mixture

2. Matter Matter is defined as anything having mass that occupies space.  Density is the measurement of matter (Mass/Vol)  The atom is the basic unit of matter  A group of similar atoms is called an element  An element cannot be separated into simpler substances by physical or chemical means.  Considered a pure substance  There are slightly more than 100 known elements. (listed on the periodic table)  The periodic table organizes elements by their properties.  Can be represented by a one or two letter abbreviation. (C,H,O,N,P,Na,Cl,Al,Ca)

3. Compounds A compound is a group of elements chemically combined in fixed ratios.  Compounds form during chemical reactions. (2H 2 + O 2  2H 2 O)  Compounds can be separated into their elements by chemical means. (2H 2 O  2H 2 + O 2 )  The symbols used to describe compounds describe the exact amount of atoms on the compound. (C 6 H 12 O 6 )  Cannot be separated by physical means.  Considered a pure substance

4. Mixtures Aggregates of substances (compounds, elements, or mixtures) physically combine to form mixtures  Mixtures can be homogeneous (Also called a solution)  Do not contain visibly different parts – milk  Particles are equally distributed  The solution is in a single phase  Mixtures can be heterogeneous  Visibly different parts  Unequally mixed  Separates under normal conditions  May be in different phases  Mixtures may be separated by physical means

5. Physical Separation  filtration – removal of a solid substance by size  distillation (boiling) – removal of a liquid substance by condensing the vapor  crystallization (evaporation) – removal of a substance that is dissolved in solution  chromatography (flowing along a stationary surface) – separated by mass (lightest travels furthest)  centrifugation (spinning to find differences in weight) - separated by mass (most massive on the outside)