10/4/20131Mon, Oct 7• Lecture 5 (Representation)– States of Matter and Physical/Chemical properties (3.1‐2)– Elements and Compounds (3.3)– Mixtures and Pure Substances (3.4‐5)– Evidence for a Chemical Reaction (6.1)• Questions we’ll answer:– Why do we care about representing matter macro‐ and microscopically? (“Lessons from Thin Air,” 3:27‐5:35)– How do we describe matter macroscopically?– How can we tell if a chemical reaction occurred?2Chemistry involves the study of matter on the molecular/atomic scalehttp://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/10/4/20132Classification of MatterSTATE (PHASE)• Gas– indefinite volume and shape– particles move in three dimensions throughout container– compressible • Liquid– definite volume, indefinite shape– particles move in three dimensions within the liquid volume– incompressible• Solid– definite volume and shape– particles can only vibrate in place– incompressible3Chlorine gasIodine gasWater + dyeMercury ClayAerogelClassification of Matter4COMPOSITION• Element: – composed entirely of the same type of atom– cannot be decomposed into other pure, stable substances• Compound: – composed entirely of the same type of molecule– can be chemically decomposed into constituent elements or other compounds• Mixture: – composed of different kinds of atoms or molecules, mixed together.– can be physically separated into constituent elements/compoundsSulfur, S8Carbon (C) nanotubesBenzene, C6H6Copper sulfate, CuSO4SeawaterMixed Candies10/4/20133Element or Compound?6Pure Substances vs MixturesPure substances cannot be separated into different components by physicalmeans.Mixtures can be separated into different components.A Homogeneous Mixture has uniform appearance and composition throughout.A Heterogeneous Mixture does not.10/4/20134Element, Compound, or Mixture?Sorting Commingled Recyclates• Comingled recycling is a heterogeneous mixture.• How could we sort it into metals, paper, glasses and plastics?http://en.wikipedia.org/wiki/Recycling#Sorting10/4/201359Chemical vs. Physical Properties of Matter• All substances have physical properties such as odor, color, shape, density, boiling point, melting point, electrical conductivity, etc. • A physical change in a substance involves a change in one or more of these physical properties, but the chemical composition remains the same.– e.g., density of liquid vs solid water• A chemical change in a substance means the chemical composition is altered (new substances are formed), which can be accompanied by changes in physical properties.– e.g., color change, temperature change, odor, fire, production of gasicewater steamDuring a physical change, the composition of the molecules stays the same, but one or more physical properties change.Physical Change vs. Chemical ChangeDuring a chemical change, the composition of the molecules changes. Chemical changes are often accompanied by physical change(s).liquid waterhydrogen gasoxygen gasPhysical properties include: odor, color, shape, density, boiling point, melting point, electrical conductivity, etc.10/4/20136Phase Changes of Water• Evaporation: a liquid becomes a gas– http://youtu.be/T5MtQ0H_tiY• Condensation: a gas becomes a liquid– http://youtu.be/bymT5AcV‐C4• Melting: a solid becomes a liquid– http://youtu.be/4od86_aV‐s8• Freezing: a liquid becomes a solid– http://youtu.be/hGmC0W6ejFg• What process occurs in this video?–