Transcript Chapter 1
Chapter 1 Matter, Energy, and the Origins of the Universe Chemistry • Chemistry is the science of matter: its composition, structure, and properties. • Matter is anything that occupies space and has mass. • Mass is a property that defines the quantity of matter in an object. For the first exam you should know the names and elemental symbols for all elements through Krypton (Kr, # 36). Classes and Properties of Matter • Types of Matter 1. Pure Substances have the same physical and chemical properties throughout. 2. Mixtures are composed of two or more substances (elements or compounds) in variable proportions. All matter is made up of either pure substances or more commonly, mixture of pure substances. A mixture contains more than one pure substance. Elements and Compounds • Most elements are not found in the world in the pure form. They are found in compounds. • Hydrogen is found in water, H2O, and other hydrogen containing compounds. • The law of constant composition states that every sample of a compound always contains the same elements in the same proportions. Pure Substances • Two Groups 1. An element is the simplest kind of material with unique physical and chemical properties. 2. A compound is a substance that consists of two or more elements linked together in definite proportions. Types of Mixtures • In homogeneous mixtures the constituents are distributed uniformly throughout the sample. • In heterogeneous mixtures the individual components can be seen as separate substances. Separating Mixtures • No chemical reactions are needed to isolate the constituents in a mixture. Filtration Distillation Filtration Physical Separation of substances by filtration Distillation Exam I (2007) • Which of the following is not a pure substance? a. nitrogen gas c. distilled water e. iron b. dry ice d. filtered seawater An Atomic View • An atom is the smallest particle of an element that retains the chemical characteristics of that element. • A molecule is a collection of atoms chemically bonded together having constant proportions. Aristotle’s view of Matter and Change. Chemical Formulas • Chemical bonds link atoms together to make molecules. • Chemical formulas use symbols to represent atoms with subscripts to identify the number of each atom present. Chemical Reactions • Chemical reactions show the transformation of one or more substance into different substances. • Chemical equations use chemical formulas to express the identities and quantities of substances involved in a reaction Properties of Matter • Intensive property - a characteristic that is independent of the amount of substance present. Examples: color, hardness, etc. • Extensive property - a characteristic that varies with the quantity of the substance present. Examples: length, width, mass, etc. Properties of Matter • Two Additional Categories of Properties 1. Physical Properties are characteristics that can be observed without changing into another substance. Examples: Luster, Hardness, Color, etc. 2. Chemical Properties are characteristics that can be observed only by reacting with another substance. Examples: Carbonates produce a gas when added to acidic solutions State of Matter • Solids have definite shapes and volumes. • Liquids occupy definite volumes, but do not have definite shapes. • Gases have neither a definite shape nor volume. Examples Making Measurements • Accurate measurements are essential for our ability to characterize the physical and chemical properties of matter. • Standardization of the units of measurements is essential. SI Base Units Quantity Unit Name Unit Abbreviation Mass Length Kilogram Meter kg m Temperature Time Kelvin Second K s Electrical Current Amount of Substance Ampere A Mole mol Luminosity Candela cd The text adds “Joule” to this list. Is this correct? Some Prefixes for SI Units http://physics.nist.gov/cuu/Units/ Binary World of SI Units Everyone doesn’t know what a megabyte is… English-Metric Conversions • 1 in = 2.54 cm Length • 1 lb = 453.6 g Mass • 1qt = 946.4 mL Volume • 1BTU = 1054-1060 J • ton of cooling =12,000BTU/hr Measurements in Scientific Studies • A measurement always has some degree of uncertainty. A digit that must be estimated is called uncertain. Accurate and precise Accuracy versus Precision in making Measurements. Precise but inaccurate Imprecise and inaccurate These terms are commonly misused by even working engineers Rules for Counting Significant Figures - Overview • Nonzero integers • Zeros leading zeros captive zeros trailing zeros • Exact numbers Rules for Counting Significant Figures - Details • Nonzero integers always count as significant figures. • 3456 has 4 sig figs. Rules for Counting Significant Figures - Details • Zeros Leading zeros do not count as significant figures. • 0.0486 has 3 sig figs. Rules for Counting Significant Figures - Details • Zeros Captive zeros always count as significant figures. • 16.07 has 4 sig figs. Rules for Counting Significant Figures - Details • Zeros • Trailing zeros are significant only if they come after a decimal point. 9.300 has 4 sig figs. Practice How many significant figures are in the following numbers? 0.04550 g 100 lb 101.05 mL 350.0 g Rules for Counting Significant Figures - Details • Exact numbers have an infinite number of significant figures. • 1 inch = 2.54 cm, exactly Rules for Significant Figures in Mathematical Operations • Addition and Subtraction: number of sig figs in the result depends on the number of decimal places in the least accurate measurement. • 6.8 + 11.934 = 18.734 18.7 (3 sig figs) Rules for Significant Figures in Mathematical Operations • Multiplication and Division: number of sig figs in the result equals the number in the least precise measurement used in the calculation. • 6.38 2.0 = 12.76 13 (2 sig figs) Practice What is the correct answer to the following problem? 1.23 g - 0.567 g = ? 0.34442 m Creation of Matter • The Big Bang Theory Explosion of a cosmic “egg” produced an expanding universe (Astronomer Georges Lemaitre). Powell Hubble demonstrated that the universe is expanding by observing the light emitted by distant stars. Scientific Method • A hypothesis is a tentative and testable explanation for an observation or a series of observations. • A scientific theory is a general explanation of widely observed phenomena that have been extensively tested. Cosmological Composition (see Dark Matter on Wikipedia) Page 33 Big Bang 1 0n 11p + Particle amu grams Neutron 1.00867 1.67494E-24 0 Proton 1.00728 1.67263E-24 +1 Electron 5.48580E-4 9.10939E-28 -1 0 -1e Charge Changing Units (Unit conversion Factors) • A unit conversion factor is a fraction in which the numerator is a quantity equal or equivalent to the quantity in the denominator, but expressed in different units. • 1kg = 1000g • Conversion factors: 1000g and 1kg 1kg 1000g Unit Conversion Examples 1. Change 18.0 mL to Liters 2. Express 2.63 pounds in milligrams 3. Express a volume of 1.250 L in m3 Density • Density is the mass of substance per unit volume of the substance: mass density = volume Using Densities A density can be used to convert masses into volumes. 8.533 g of Iron 1 mL 7.87 g of Fe = 1.08 mL Practice The density of Ti is 4.50 g/cm3. What is the volume of 7.20 g of Titanium? Exam I (2007) • If the concentration of mercury in the water of a Berkeley pit mine-lake is 0.25 mg per liter of waste water, what is the total mass of Hg in the “lake”? Assume that The Pit has a surface area of 1.00 square mile and an average depth of 700. ft (and rising). Temperature Scales Practice The lowest temperature measured on the Earth is -128.6oF recorded at Vostok, Antarctica in July 1983. What is this temperature in oC and in Kelvin? ChemTour: Big Bang Click to launch animation PC | Mac This animation explores the concept of the early formation of matter and radioactive decay rates within the context of the Big Bang. ChemTour: Significant Figures Click to launch animation PC | Mac This ChemTour reviews the rules for assigning significant figures and walks students through sample calculations. ChemTour: Scientific Notation Click to launch animation PC | Mac This ChemTour explains how to use scientific notation to express very large and very small numbers, and how to easily convert back and forth between decimal numbers and scientific notation. ChemTour: Dimensional Analysis Click to launch animation PC | Mac Students learn to keep track of the units associated with numerical values. The ChemTour includes worked examples and interactive Practice Exercises. ChemTour: Temperature Conversion Click to launch animation PC | Mac Students practice converting between Fahrenheit, Celsius, and Kelvin temperature scales.