CHEMISTRY. CHM201 Class #2 CHEMISTRY. Chapter 1 Continued. Chapter 1 Outline for Class #2. Particles of Matter: Measurements and the Tools of Science

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1 CHEMISTRY Fifth Edition Gilbert Kirss Foster Bretz Davies CHM201 Class #2 Chemistry, 5 th Edition Copyright 2017, W. W. Norton & Company CHEMISTRY Fifth Edition Gilbert Kirss Foster Bretz Davies Chapter 1 Continued Particles of Matter: Measurements and the Tools of Science Chemistry, 5 th Edition Copyright 2017, W. W. Norton & Company Chapter 1 Outline for Class #2 1.8 SI Units 1.9 Unit Conversion and Dimensional Analysis 1.10 Evaluating and Expressing Experimental Results 1.11 Testing a Theory: The Big Bang Revisited 3 1

2 Prefixes for SI Units 4 Six SI Base Units 5 SI Units and U.S. Customary Units 6 2

3 Changing Units: Conversion Factors Unit conversion factor A fraction in which the numerator is equivalent to the denominator, even though they are different units, making the value of the fraction one: 1 km mi or 1 km = mi mi 1 km Converting a value from one unit to another: 7 Changing Units: Conversion Factors If a car travels a distance of 241 km, what is that distance in miles? 8 Significant Figures All measurements contain uncertainty. Depends on instruments used to make measurement A digit that must be estimated is called uncertain (last recorded digit). ± 0.01 g ± g 9 3

4 Significant Figures Includes all digits known with certainty plus one digit that is uncertain (estimated) Rules for counting significant figures: All nonzero integers are significant. Zeros (depends on location): Leading zeros Trailing zeros Captive zeros Exact numbers 10 Counting Significant Figures Nonzero integers are always significant sig. figs sig. figs. Zeros Leading zeros are not significant sig. figs sig. figs. 11 Counting Significant Figures Zeros Trailing zeros are not significant unless they come after a decimal point sig. figs sig. figs. Captive zeros are always significant sig. figs sig. figs. Exact numbers have an infinite number of significant figures. 12 4

5 13 Counting Significant Figures Summary 1. Start counting at the first nonzero digit and count to the last nonzero digit. 2. If there is a decimal point in the number, count all the way to the end of the number. Practice: Counting Sig. Figs. How many significant figures are in the following numbers? g =?? 100 lb =?? ml =?? g =?? 14 Practice: Counting Sig. Figs. How many significant figures are in the following numbers? g The leading zeros are not significant, but the trailing zero is significant. (4 sig. figs.) 100 lb Without a decimal point, these trailing zeros are not significant. (1 sig. fig.) ml All nonzero integers, plus the captured zeros (5 sig. figs.) g The presence of the decimal point makes the trailing zeros significant. (4 sig. figs.) 15 5

6 Sig. Figs. in Mathematical Operations Rounding off Drop insignificant digits Only at the end of calculations! Weakest link principle The number of significant figures in the final result cannot be greater than the weakest link used in the calculation. The actual rule depends on the mathematical operation. 16 Sig. Figs. in Mathematical Operations Multiplication/Division: Number of sig. figs. in the result = Number in the least precise measurement used in the calculation = = = = 6.63 (2 sig. figs.) (3 sig. figs.) 17 Sig. Figs. in Mathematical Operations Addition/Subtraction: Number of significant figures in the result depends on the number of decimal places in the least accurate measurement = = = = 35.6 (3 sig. figs.) ( 3 sig. figs.) 18 6

7 Sig. Figs. in Mathematical Operations Calculations that involve multiple steps: To determine the number of significant figures, we must first perform individual operations to determine the number of significant figures at each step g g = g/cm cm The first step involves performing the subtraction in the numerator g 0.567g = g In this step there should only be two significant figures. = 0.66 g 3 19 Sig. Figs. in Mathematical Operations With only two significant figures in the numerator there can only be two significant figures in the final answer g g = g/cm cm = g/cm 3 20 Precision and Accuracy Accuracy Agreement between a measured value and the accepted or true value Precision Agreement among repeated measurements 21 7

8 Calculations for Precision and Accuracy Mean ( X ) An average calculated by summing a set or related values and dividing the sum by the number of values in the set ( ) i x i x = i ( x ) Represents the sum of all the individual n Represents the number of values n i x i values 22 Calculations for Precision and Accuracy Standard deviation(s) A measure of the amount of variation, or dispersion, in a set of related values s = ( x x) i i n 1 2 ( x) 2 i x i Represents the sum of all the individual numbers minus the average squared n Represents the number of values 23 Calculations for Precision and Accuracy Confidence interval A range of value that has a specific probability of containing the true value of a measurement To calculate the confidence interval we use a statistical tool called the t-distribution: = x ts n 24 8

9 Calculations for Precision and Accuracy Confidence interval = x ts n s Represents standard deviation n Represents the number of values t Represents a value based upon confidence level and number of values 25 Temperature Scales Fahrenheit ( F) Celsius ( C) Kelvin (K) Temperature conversions: K = C C = 5/9 ( F 32) F = 9/5 C Practice: Temperature Conversions The lowest temperature measured on the Earth is F, recorded at Vostok, Antarctica, in July What is this temperature in C and in Kelvin? Collect and Organize: We are given the temperature in F and asked to convert it to C and Kelvin. Temperature = F C = 5/9 ( F 32) K = C

10 Practice: Temperature Conversions The lowest temperature measured on the Earth is F, recorded at Vostok, Antarctica, in July What is this temperature in C and in Kelvin? Analyze 5 C = ( F - 32) 9 5 K = ( F - 32) Practice: Temperature Conversions The lowest temperature measured on the Earth is F, recorded at Vostok, Antarctica, in July What is this temperature in C and in Kelvin? Solve 5 C = ( F - 32) = C 9 5 K = ( F - 32) = 183.9K 9 29 Practice: Temperature Conversions The lowest temperature measured on the Earth is F, recorded at Vostok, Antarctica, in July What is this temperature in C and in Kelvin? Think About It Since the Fahrenheit scale has smaller degrees than the Celsius scale, a value that is less negative on the Celsius scale seems reasonable. Adding to this produces a positive value on the Kelvin scale, which is reasonable since you cannot have a value less than absolute zero on the Kelvin scale

11 The Big Bang Revisited Robert Dicke (1960s) Predicted that residual energy from the Big Bang could be measured as microwave energy Robert W. Wilson and Arno A. Penzias (1978) Shared Nobel Prize in Physics for discovery of cosmic microwave background radiation of the universe COBE satellite data Supports the theory that the universe did not expand and cool uniformly 31 Visual Problems 1. Which figures, if any, depict a chemical reaction? 32 Visual Problems 2. List the molecules that are elements

12 Visual Problems 3. Which molecule contains the most atoms? 34 CHEMISTRY Fifth Edition Gilbert Kirss Foster Bretz Davies Chapter 2 Atoms, Ions, and Molecules: Matter Starts Here Chemistry, 5 th Edition Copyright 2017, W. W. Norton & Company Particulate Review Helium Is helium an element, an ionic compound, or molecular compound? A. Element B. Ionic Compound C. Molecular Compound 36 12

13 Particulate Review Gold Is gold an element, an ionic compound, or a molecular compound? A. Element B. Ionic Compound C. Molecular Compound 37 Particulate Review Ethanol Is ethanol an element, an ionic compound, or a molecular compound? A. Element B. Ionic Compound C. Molecular Compound 38 Particulate Review Sodium Chloride Is sodium chloride an element, an ionic compound, or a molecular compound? A. Element B. Ionic Compound C. Molecular Compound 39 13

14 Particulate Preview Is the image above an element, an ionic compound, or a molecular compound? A. Element B. Ionic Compound C. Molecular Compound 40 Chapter 2 Outline for Class #2 2.1 Atoms in Baby Teeth 2.2 The Rutherford Model 2.3 Isotopes and Symbols 41 Atomic Structure: Electrons J.J. Thomson, a British scientist, discovered electrons in Beam from cathode ray tube is deflected toward positively charged plate. Atoms contain negatively charged particles (electrons) with a constant mass-to-charge ratio

15 Mass of an Electron Robert Millikan, an American physicist, determined the mass and charge of an electron with his oil-drop experiment in e = x C Mass of an electron = x g 43 Thomson s Model of the Atom Plum-pudding model: e distributed throughout diffuse, positively charged sphere 44 Radioactivity and the Nuclear Atom Henri Becquerel, French physicist (1896) Some materials produce invisible radiation, consisting of charged particles. Radioactivity Spontaneous emission of high energy radiation and particles Beta particles (, high energy electrons) Alpha particles (, +2 charge, mass = He nucleus) 45 15

16 Atomic Structure: the Nucleus Rutherford s (New Zealand) gold foil experiment: Bombard a thin gold foil with particles to test Thomson s model of the atom. 46 Rutherford s Experiment Expected results from plumpudding model Actual results 47 The Nuclear Atom James Chadwick, English physicist Bombarded a thin sheet of beryllium with particles; a very high energy radiation was emitted by the metal that was not deflected by either electric or magnetic fields. The radiation consisted of a third type of subatomic particle, which Chadwick named neutrons because they were electrically neutral particles having a mass slightly greater than that of protons

17 The Nuclear Atom The nucleus: Is the positively charged center of an atom, containing nearly all of the atom s mass. Is about 1/10,000 the size of the atom. Consists of two types of particles: Protons: positively charged subatomic particles Neutrons: electrically neutral subatomic particles 49 The Nuclear Atom Nucleus has protons (+ charge) plus neutrons (neutral). Distance is measured in picometers (pm). 50 Atomic Mass Units Atomic mass units (amu) Unit used to express the relative masses of atoms and subatomic particles Equal to 1/12 of a carbon atom: 6 protons + 6 neutrons = 12 amu 1 amu = 1 Dalton (Da) Named for the English chemist John Dalton 51 17

18 The Nuclear Atom: Summary 52 Aston s Positive-Ray Analyzer Ne gas ions of different masses strike the detector in different locations. 53 Aston s Experiment Positive-ray analyzer results: Two different kinds of neon gas atoms exist. 90% = 20 amu 10% = 22 amu Aston proposed theory of isotopes. Isotopes Atoms of an element containing the same number of protons but different numbers of neutrons 54 18

19 Symbols of Isotopes Mass number (A) total number of nucleons (protons + neutrons) in the nucleus A Z X Elemental symbol a one- or two-letter symbol to identify the type of atom. Frequently called a Nuclide symbol. Atomic number (Z) the number of protons in the nucleus; determines the identity of the element 55 Symbols of Isotopes A Z Most elements have two or more isotopes, atoms that have the same atomic number (Z) but different mass numbers (A) U 92 U = 143 neutrons = 146 neutrons X 56 Practice: Isotopic Symbols A Use the format Z X to write the symbol for the nuclides having 15 protons and 17 neutrons. Collect and Organize: We have 15 protons and 17 neutrons. Analyze: Number of protons represent the A and tells us what element we are looking for. The total number of nucleons (protons + neutrons) represents the Z

20 Practice: Isotopic Symbols A Use the format Z X to write the symbol for the nuclides having 15 protons and 17 neutrons. Solve: P Think About It: Phosphorus is the 15th element on the periodic table =