Introduction: Matter and Measurement SC 131 CHEM 1 Chemistry: The Central Science CM Lamberty Homework Chapter 1 Exercises (p 31-35) 12, 36, 42, 56, 14, 18, 20, 22, 24, 26, 28, 30, 32 40 46, 48a, 50, 52 58, 60, 62, 65, 68, 71, 72, 78 Chemistry The study of materials and the changes that materials undergoes Where is chemistry present in your life? The Study of Chemistry The Atomic and Molecular Perspective Matter Property Anything with mass and occupies space Characteristic that helps recognize a type of matter and distinguish from other types Elements 100+ basic substances that make up matter either alone or in various combinations The Study of Chemistry Atom: submicroscopic particles Fundamental building blocks Molecules Two or more atoms joined in specific geometric arrangement Bonds Electronic force that holds atoms together in molecule The Study of Chemistry Why Study Chemistry? Impacts daily lives Informs citizens Fulfills curriculum requirements Classification of Matter Substance: specific instance of matter Solid: mq close and little movement Fixed volume, rigid shape Crystalline or amorphous Liquid: mq close but free to move Fixed volume, no fixed shape Gas: mq far apart, compressible No fixed volume, no fixed shape Classification of Matter Classification according to Composition Kinds and amt of substances that make up matter Pure substance: single type of atom/mq Element—cannot be broken down further Compound—can be broken down into elements Fixed definite composition Mixture Heterogeneous Homogeneous Physical & Chemical Properties Physical Property—displays w/o changing appearance Examples Chemical Property—only displayed by changing composition Examples Physical & Chemical Changes Physical Change Alter only appearance not composition Ex Chemical Change Composition changes Ex Separation of Mixtures Individual sorting by color or shape Use of physical properties Magnetic Filtration Distillation Chromatography Chemical reactivity One substance reacts while the other does not. Need to be able to get back original substance. The Scientific Approach to Knowledge Empirical Hypothesis Highly controlled experiments reproducible Theory Tentative explanation of observations Experiments Observation and experimentation Well-established hypotheses Scientific Law Summarize past observations and predicts future ones Units of Measurements International System of Units (SI) Length Mass m Kilogram m kg Time Second s Temperature Kelvin K Amt of Subst Mole mol Electric current Ampere A Luminous intensity Candela cd Length and Mass Length Meter Distance light (598 nm) travels in 1 second Just a bit more than a yard Mass Amount of material in an object Not weight (which is a force) 1 kg ~ 2.2 pounds Cube of Platinum in Sorbonne???? Temperature Hotness or coldness of an object Direction of heat flow Heat flows from higher T to lower T spontaneously Celsius and Kelvin Kelvin is absolute scale and does not have negative values Conversion Factor °F = 1.8(°C) + 32 K = °C + 273.15 Derived Units Combination of other units Volume—amount of space matter occupies Vol of cube = (edge length)3 Liter or milliliter (L or mL) for liquids Density—mass per unit volume Density = mass/volume = m/V Intensive vs. Extensive Properties Intensive—independent of the amount of substance Extensive—dependent upon the amount of substance Uncertainty in Measurement Precision vs. Accuracy Precision is measure of how closely individual measurements agree with one another Accuracy is how closely measurement agrees with the correct or “true” value Perform several trials and average the results Standard deviation reflects how much results differ from average Significant Figures Uncertainty in Measurement Scientific measurements are reported so that every digit is certain except the last, which is estimated. Uncertainty in Measurement Significant Figures—only for measured values The greater the number of significant figures, the greater the certainty fo the measurement Exact Numbers—actual counts No uncertainty, unlimited sig fig Significant Figure Rules All nonzero digits are significant Interior zeros are significant Leading zeros are not significant Trailing zeros After decimal point always significant Before decimal point are significant 3.9000 40.00 Before implied decimal point are ambiguous 1200 use sci notation 1.200 x 103 or 1.20 x 103 Significant Figures in Calculations Multiplication/division—result uses fewest number of sig fig Addition/subtraction—fewest number of decimal places Rounding—4 or less round down, 5 or greater round up Round at the end of all calculations not individual steps Calculators are stupid & do not know rules Solving Chemical Problems Generally 2 types: Unit conversion (dimensional Analysis) or specific equation Dimensional Analysis Calculate the displacement of a 5.70 L automobile engine in cubic inches Watch units raised to a power and account for that mathematically General Problems Solving Strategy Identify starting point (given info) Identify the end point (what you want) Devise a way to get from start to end— conceptual plan Sort Strategize Solve Check