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Chap 3: Atoms & the Periodic Table 1 Pre-Question #1 What is an atom? What particles make up an atom? The basic unit of matter Electrons, protons, and neutrons What are three laws that support the existence of atoms? Law of definite proportions Law of conservation of mass Law of multiple proportions 2 Fold 2 pieces of paper as instructed Label the bottom Law of definite proportions Law of conservation of mass Law of multiple proportion On top, write 3 bullets points each of what you learned from your reading 3 3-1. Foundations of Atomic Theory The Laws of Definite Law of definite proportion- in samples of any chemical compound, the _____ massesof the samples are always in the _____ same ______ proportions ex: In water, there will always be 8 g O for 1 g of H. 16 g O = 8 g O 2gH 1gH 16 g 1g 1g 4 Chapter 3 Visual Concepts Law of Definite Proportions 5 The Law of Conservation of Mass The mass of the reactant in a reaction equals the mass of the product 6 Chapter 3 Visual Concepts Law of Conservation of Mass 7 Law of multiple proportion- whenever 2 elements form more than one compound, the different ______ masses of one element that same mass of the other combine with the _____ element are in the ratio of small whole numbers Ex: compare water and peroxide. Both molecules have the same number of H but different number of O, so the ratio is 1:2. water peroxide 8 Chapter 3 Visual Concepts Law of Multiple Proportions 9 CO carbon CO2 monoxide carbon dioxide 10 3-1. Development of Atomic Models 1. 2. Greek model(300’s BC): Democritus believed matter cannot be broken atoms forever_____ Dalton’s atomic theory (pg 78): a. b. c. d. e. Elements are composed of indivisible atoms If same element, then same atoms Cannot be subdivided, created, or destroyed Can physically mix; can chemically combine in whole # ratio Chem. Rxn occur when atoms separate, join, or rearrange 11 Chapter 1 Section Review What is the atomic theory? The theory that all matter is composed of atoms What is a compound? A compound is a substance made from two or more kinds of atoms 12 State the law of definite proportions, conservation of mass and multiple proportions Law of definite proportions Each sample of a given compound contains the same elements in the same proportions by mass regardless of the size or source of the sample Law of conservation of mass Mass is neither created nor destroyed during a chemical reaction Law of multiple proportions When the same elements combine to form different compounds, they do so in mass ratios that can be expressed by small, whole numbers. 13 According to Dalton, what is the difference between an element and a compound? Element=composed of atoms, all have identical properties Compound= two or more kinds of atoms, with different properties, combined in a simple, whole number ratio Which of Dalton’s five principles still apply to the structure of an atom? Principles 3,4,5 Principle 1= atoms can be divided into subatomic particles Principle 2= isotopes exist with same atom, different properties 14 What law is described by the fact that carbon dioxide consists of 27.3% carbon and 72.7% oxygen by mass? Law of definite proportions What law is described by the fact that the ratio of the mass of oxygen in carbon dioxide to the mass of oxygen in carbon monoxide is 2:1? Law of multiple proportions 15 Three compounds contain the element sulfur and fluorine. How do the following data support the law of multiple proportions? Compound A: 1.188g F for 1.000g S Compound B: 2.375g F for 1.000g S Compound C: 3.563g F for 1.000g S Three compounds have masses of F combined with 1.000g of S in a ratio of small, whole numbers. The ratio is 1.2.3 Law of multiple proportions 16 Atoms and Periodic Table 17 3. 4. 5. protons positive Goldstein (1886): discovered______, particles, observed canal rays traveling opposite cathode rays e- using a cathode-ray Thomson: discovered __ tube(1897); its mass is about 1/2000 of a hydrogen atom(1900) Fig 3-4, 3-5 Rutherford (1911): atom mostly empty space with dense _______ nucleus 6. Fig 3-6: gold foil experiment Gold Foil Experiment one unit Millikan(1916): e- carries ___ ___ of negative 1/1840 of a charge and has a mass of ______ 7. hydrogen atom neutron no Chadwick (1932): discovered _______, charge, same mass as a proton a. 18 Chapter 3 Visual Concepts Comparing Models of Atoms 19 Chapter 3 Visual Concepts Thompson’s Cathode Ray Tube Experiment 20 Chapter 3 Visual Concepts Rutherford’s Gold Foil Experiment 21 3-2 Subatomic Particles 1. Nucleus: a. b. 99.9% mass protons Isotope: same # of ______, different # of _______; neutrons - ex. 3 different isotopes of Ne: Ne-20, Ne-21, Ne-22 c. d. e. 2. p+ = 1.673 x 10^-27 kg Atomic mass = ______ _______ protons +neutrons Atomic number = # of _______ protons Electron: a. b. Around the nucleus in a specific energy level (Bohr) 9.109 x 10^-31 kg 22 Symbols Contain the symbol of the element, the mass number and the atomic Mass number. number Atomic number X We can also put the mass number after the name of the element for different isotopes carbon- 12, carbon -14 Tr 12A Table 3 p. 83 Properties of Subatomic Particles Which is the smallest? The Electron Describe the information conveyed by each symbol. The 1st symbol only shows the relative charge (use when that’s all you need). The 2nd also shows the mass number. SUBATOMIC PARTICLE 24 Subatomic Particles ATOM ATOM NUCLEUS NUCLEUS PROTONS PROTONS POSITIVE POSITIVE CHARGE ELECTRONS ELECTRONS NEUTRONS NEUTRONS NEGATIVE CHARGE NEGATIVE CHARGE NEUTRAL NEUTRAL CHARGE CHARGE equal in a Atomic Most ofNumber the atom’s mass. QUARKS neutral atom equals the # of... 25 B. Isotopes Atoms of the same element with different mass numbers. Nuclear symbol: Mass # Atomic # Hyphen notation: carbon-12 12 6 C 26 Example Problem 1. Give the Atomic number of the element shown. Ans. 9 2. Give the number of protons and electrons for this element. Ans. 9 p+ and 9 e3. Give the mass number of the Ans. 19 element shown. 4. Give the number of neutrons for this element.Ans. 10 19 9 F # of n0 = mass # - atomic # # of n0 = 19 – 9 = 10 n0 Pre-Question #3 how many protons, neutrons and electrons are in an atom of sodium with atomic number of 11? Atomic mass = 23 = # of protons + neutron Atomic number = 11 = # of protons and electrons Atomic mass – atomic number = # of neutron Therefore, 11 proton, 11 electron 12 neutron 28 29 B. Isotopes 30 © Addison-Wesley Publishing Company, Inc. B. Isotopes Chlorine-37 atomic #: 17 mass #: 37 # of protons: 17 # of electrons: 17 # of neutrons: 20 37 17 Cl 31 Isotope 32 Chapter 3.2 Section Review Describe the difference between electrons, protons and neutrons. Electron the mass is much smaller than proton and neutron. -1 charge Surrounds the nucleus Proton and Neutron Make up atomic nucleus +1 and no charge, respectively 33 How are isotopes of the same element alike? What subatomic particle was discovered with the use of a cathode-ray tube? All isotopes of an element have the same number of protons and electrons Electron Write the symbol for element X, which has 22 electron 34 Determine the number of electrons, protons and neutrons for each of the following 80-Br 106-Pd 46 e 46 p, 60 n 133-Cs 35 e, 35 p, 45 n 55 e, 55 p, 78 n Calculate the atomic number and mass number of an isotope that has 56 electrons and 82 neutrons Atomic number = 56 Mass number 138 35 Why must there be an attractive force to explain the existence of stable nuclei? If the repulsive force between positively charged protons were the only force, a nucleus could not contain multiple protons. Are hydrogen-3 and helium-3 isotopes of the same element? Explain your answer No, they are isotopes of different elements, because they have different atomic numbers. All isotopes of an element have the same atomic number, not the same mass number. 36 3-4 Atomic Mass Mass of atom at rest Refers to ONE atom The mass of an atom expressed in atomic mass units amu = atomic mass unit the ratio of the average mass per atom of the element to 1/12 of the mass of 12C in its nuclear and electronic ground state. Hydrogen = 1amu, 1/12 of C 37 Atomic Weight the abundance-weighted average mass of an element Based on abundance of each element in nature. Each isotope has its own atomic mass, thus we determine the average from percent abundance. Is not a whole number because it is an average. are the decimal numbers on the periodic table. Commonly reported in amu or grams/mol Calculating Atomic Mass Carbon has two stable isotopes Carbon-12 has natural abundance of 98.89% and 12.000 amu Carbon-13 has natural abundance of 1.11% and 13.003 amu Calculate the atomic mass 39 Carbon has two stable isotopes Carbon-12 has natural abundance of 98.89% and 12.000 amu Carbon-13 has natural abundance of 1.11% and 13.003 amu Calculate the atomic mass 1. 2. 3. Givens Carbon-12 m=12.000 amu Abundance= 98.89%=0.9889 Carbon-13 m = 13.0003 amu Abundance = 1.11%=0.0111 Formula atomic mass of carbon-avg = (mass C-12 x nat.abund) + (mass C-13 x nat.abund.) Plug in the #s (12.000amu x 0.9889) + (13.003 amu x 0.0111) = 12.011 amu = 12.0 amu 40 Chemical Quantities? You can measure mass, volume,or you can count particles. measure mass in grams. measure volume in liters. We count particles in MOLES. Mole is abbreviated: mol 41 What is the Mole? A counting number (like a dozen) 6.02 x 1023 is called Avogadro’s number. 1 mol = 6.02 1023 items ( representative particles) A large amount!!!! 42 1 mole of hockey pucks would equal the mass of the moon! 1 mole of basketballs would fill a bag the size of the earth! 1 mole of pennies would cover the Earth 1/4 mile deep! 43 Molar Conversion Examples How many atoms are in 2.50 moles of C? 24 1.51 10 2.50 mol 6.02 1023 atoms =atoms C 1 mol 44 Example 1. Calculate the # of atoms in 0.500 mol of Al. 1) Ans: 3.01 x 1023 Al atoms 0.500 mol Al x 6.02 x 1023 Al atoms 1 mol Al 2. Calculate the # of moles of Na if a sample of Na contains 1.80 x 1024 Na atoms. 2) Ans: 2.99 mole Na 1.8 x 1024 Na atoms x 1 mol Na 6.02 x 1023 Na atoms 45 Molar Mass - Is the Mass (in Grams) of One Mole of a Substance (often called molecular weight) Molar mass or MM ___ is the generic term for the mass of one mole of any substance (in grams) The same as: 1) gram molecular mass or gmm ___ (molecules) 2) gram formula mass or ___ gfm (ionic compounds) 3) gram atomic mass or gam ___ (elements) 46 Molar Mass of Elements = atomic mass (simply look at the periodic table) carbon 12.01 g/mol aluminum 26.98 g/mol zinc 65.39 g/mol 47 Mass to Mole Conversion How many moles of carbon is 26 g of carbon? (find MM of C from the periodic table) 26 g C 1 mol C 12.01 g C = 2.2 mol C 48 Mass to Mole Conversion How many moles is 5.69 g of Na? Na = 22.99 g/mol 5.69 g Na 1 mol Na = 0.247 mol Na 22.99 g Na 49 Mole to Mass Conversion How many grams are in 9.45 mol of nitrogen atoms? N = 14.01 g/mol 9.45 mol N 14.01 g N 1 mol N = 132.39 =132 g N 50 Molar Conversions MASS molar mass ÷ X NUMBER MOLES IN GRAMS 6.02 1023 OF X ÷ (g/mol) (particles/mol) PARTICLES 51 Test Prep: How many moles of carbon-12 are contained in exactly 6 grams of carbon12? 1. 2. 3. 4. 0.5mole 2.0moles 3.01 ×1023 moles 6.02 ×1023 moles 52 Test Prep How many atoms are contained in 97.6 g of platinum (Pt)? 1. 2. 3. 4. 5.16 × 1030 3.01 × 1023 1.20 × 1024 1.10 × 1028 53 What about compounds? Mass in grams of 1 mole equal the sum of the atomic masses What is the mass of one mole (molar mass) of CH4? 1 C = 12.01 g/mol 4 H x 1.01 g/mol = 4.04g/mol 1 mole CH4 = 12.01g/mol + 4.04 g/mol =16.05g/mol 54 Molar Mass Example Problem Find the molar mass of sodium bicarbonate NaHCO3 22.99g/mol + 1.01g/mol + 12.01g/mol + 3(16.00 g/mol) = 84.01 g/mol 55 Example Problem Prozac, C17H18F3NO, is a widely used antidepressant that inhibits the uptake of serotonin by the brain. It has a molar mass of 1) 40.0 g/mole 2) 262 g/mole 3) 309 g/mole Solution: 17C (12.0) 18H (1.0) 3F (19.0) 1N (14.0) + 1 O (16.0) 309 g/mole 56 Mass to Mole Conversion How many moles is 5.69 g of NaOH? (Find MM of NaOH) Na = 22.99 g/mol O = 16.00 g/mol H = 1.01 g/ mol 40.00 g/mol 5.69 g NaOH 1 mol NaOH = 0.142 mol NaOH 40.00 g NaOH 57 Mole to Mass Conversion How many grams are in 9.45 mol of dinitrogen trioxide? N2O3 = 2(14.01) + 3(16.00) = 76.02 g/mol 9.45 mol N2O3 76.02 g N2O3 = 718.2 =718 g N2O3 1 mol N2O3 58 Representative particles The smallest pieces of a substance. molecular compounds: molecule. ionic compounds: formula unit. elements: atom. 59 Questions How many atoms in the following cmpds? CaCO3 5 Al2(SO4)3 17 How many oxygen atoms in the above cmpds? 3 12 60 A Moles of Particles Contains 6.02 x 1023 particles 1 mole C = 6.02 x 1023 C atoms 1 mole H2O = 6.02 x 1023 H2O molecules 1 mole NaCl = 6.02 x 1023 NaCl formula units 61 Another Example How many atoms of oxygen are there in 1.23 moles of CO2 ? 23 molecules CO 6.02 x 10 1.23 mol CO2 2 2 atoms O 1 mol CO2 1 molecule CO2 = 1.48 x 1024 atoms O 62 More Molar Conversion Examples the mass of 2.1 1024 molecules of NaHCO3. Find 2.1 1024 molecules 1 mol 84.01 g 6.02 1023 1 mol molecules = 290 g NaHCO3 63 Practice Problems = .104 mol 1. How many moles is 4.56 g of CO2? 2. How many grams is 9.87 moles of = 178 g H2O? 3. How many molecules is 6.8 g of 23 molec = 2.6 x 10 CH4? 4. How much would 3.45 x 1022 atoms of U weigh? = 13.6 g 64 Chapter 3 Standardized Test Preparation Understanding Concepts 2. Which of these is always equal to the number of protons in an atom? F. the mass number G. the number of isotopes H. the number of neutrons I. the number of electrons Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Standardized Test Preparation Understanding Concepts 2. Which of these is always equal to the number of protons in an atom? F. the mass number G. the number of isotopes H. the number of neutrons I. the number of electrons Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Standardized Test Preparation Understanding Concepts 3. Which of these events occurs when an electron in an excited state returns to its ground state? A. Light energy is emitted. B. Energy is absorbed by the atom. C. The atom undergoes spontaneous decay. D. The electron configuration of the atom changes. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Standardized Test Preparation Understanding Concepts 3. Which of these events occurs when an electron in an excited state returns to its ground state? A. Light energy is emitted. B. Energy is absorbed by the atom. C. The atom undergoes spontaneous decay. D. The electron configuration of the atom changes. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Standardized Test Preparation Reading Skills 7. The model of the atom has changed over time because F. earlier models were proven to be wrong. G. electrons do not revolve around the nucleus. H. as new properties of atoms were discovered, models had to be revised to account for those properties. I. new particles were discovered, so the model had to be changed to explain how they could exist. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Standardized Test Preparation Reading Skills 7. The model of the atom has changed over time because F. earlier models were proven to be wrong. G. electrons do not revolve around the nucleus. H. as new properties of atoms were discovered, models had to be revised to account for those properties. I. new particles were discovered, so the model had to be changed to explain how they could exist. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Standardized Test Preparation Reading Skills 8. Why do scientists need models as opposed to directly observing electrons? A. Models can be changed. B. There is no technology that allows direct observation of electrons. C. The charges on the electrons and protons interfere with direct observation of the atom. D. Scientists cannot measure the speed of electrons with sufficient accuracy to determine which model is correct. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Standardized Test Preparation Reading Skills 8. Why do scientists need models as opposed to directly observing electrons? A. Models can be changed. B. There is no technology that allows direct observation of electrons. C. The charges on the electrons and protons interfere with direct observation of the atom. D. Scientists cannot measure the speed of electrons with sufficient accuracy to determine which model is correct. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Standardized Test Preparation Reading Skills 9. What would cause scientists to change the current model of the atom? Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Standardized Test Preparation Reading Skills 9. What would cause scientists to change the current model of the atom? Answer: The current model of the atom would change if new data were found about atoms that could not be explained by the existing model. The new model would explain both the new data and all earlier observations. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Thomson’s Experiment Voltage source - + Vacuum tube Metal Disks Some History on The Discovery of the Atom Discovery of The Electron: J.J. Thomson and the Cathode Ray Tube (1897) Calculated e-/m 76 Thomson’s Experiment Voltage source Passing + an electric current makes a beam appear to move from the negative to the positive end Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field he found that the moving pieces were negative Rutherford’s experiment Alpha particles - positively charged particles- helium atoms minus electrons Shot them at gold foil which can be made a few atoms thick. When an alpha particle hits a fluorescent screen, it glows Some History on The Discovery of the Atom Rutherford’s Gold Foil Experiment and the Discovery of the Nucleus Believed in Plum Pudding Model Wanted to see How Large Atoms are 81 Lead block Uranium Fluorescent Screen Gold Foil He Expected The alpha particles to pass through without changing direction very much. Because…? …the positive charges were thought to be spread out evenly. Alone they were not enough to stop the alpha particles. What he expected Because He thought the mass was evenly distributed in the atom Since he thought the mass was evenly distributed in the atom What he got How he explained it Atom is mostly empty. Small dense, positive piece at the center-the nucleus. Alpha particles are deflected by it, if they get close enough. + Almost no deflection; few greatly deflected + History of Atom Smallest possible Democritus looked at piece? beach (400 B.C.) Made of sand Atomos - not to be cut Cut sand - smaller sand