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Student Name: ________________________________________ Per: __________ Date: __ / __ / __ Score: ______ LEARNING GUIDE 11: ATOMIC MODELS BEFORE YOU START Learning the atomic models involves appreciating the history of chemistry, understanding the importance of laws, and helps students understand theories may be changed as new data are collected and discussed. There are numerous models and you must memorize their different features. Students should be able to compare and contrast these models and explain how they were developed. STATE CONTENT STANDARDS State Standard 1: The periodic table displays the elements in increasing atomic number and shows how periodicity of the physical and chemical properties of the elements relates to atomic structure. MAJOR CONCEPTS Lesson 37: Subatomic particles Lesson 38: Dalton’s atomic theory o Students learn the major atomic models o Describe Democritus’ ideas about atoms o Describe the size of an atom Lesson 39: Describe J. J. Thomson’s model of the atom Lesson 40: Rutherford’s nuclear model Lesson 41: Bohr model: Introduction Lesson 42: Wave model: Introduction Lesson 43: Standard model VOCABULARY Define each vocabulary word. Nuclear atom Subatomic Excited state Nucleus Photon Ground state www.thechembook.com Page 1 Learning Guide: 11 READING Part I: Important Facts (List seven important facts found during the reading) Section 3.3 1. _______________________________________________________________ 2. _______________________________________________________________ 3. _______________________________________________________________ 4. _______________________________________________________________ 5. _______________________________________________________________ 6. _______________________________________________________________ 7. _______________________________________________________________ Section 3.5 1. _______________________________________________________________ 2. _______________________________________________________________ 3. _______________________________________________________________ 4. _______________________________________________________________ 5. _______________________________________________________________ 6. _______________________________________________________________ 7. _______________________________________________________________ Section 11.1 1. _______________________________________________________________ 2. _______________________________________________________________ 3. _______________________________________________________________ 4. _______________________________________________________________ 5. _______________________________________________________________ 6. _______________________________________________________________ 7. _______________________________________________________________ www.thechembook.com Page 2 Learning Guide: 11 Part II: Summaries (3.6, 11.5, and 11.6 are not included here but you should read them.) Using one paragraph per section, summarize the three sections you just read. Section 3.3 _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ Section 3.5 _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ Section 11.1 _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ www.thechembook.com Page 3 Learning Guide: 11 READING GUIDE 3.3: Title: ______________________________________________________ 1. What does the law of constant composition mean? 2. Although Dalton’s atomic theory was rejected at first, he used his theory to do WHAT that soon resulted in his theory being accepted by scientists? 3.5: Title: ______________________________________________________ 3. Because of the success of Dalton’s theory, scientists came to believe what two things? 4. How did J.J. Thomson know that the particles he had discovered were negatively charged? 5. Today, the particles discovered by Thomson are called __________________. 6. Why did Thomson then conclude that atoms must also have positively charged particles? www.thechembook.com Page 4 Learning Guide: 11 7. Describe J. J. Thomson’s plum pudding model of the atom. 8. Rutherford was a student of ______________________ and designed an experiment in which ___________________-charged alpha () particles were directed at a _______ _________ _______. 9. What did Rutherford expect the particles to do? 10. What were the results of Rutherford’s experiment? 11. What must have caused the large deflections of the particles? 12. Why did most of the particles pass directly through the foil? www.thechembook.com Page 5 Learning Guide: 11 13. Describe Rutherford’s nuclear atom. 14. The neutron was discovered in 1932 by Rutherford and _________________________. CHAPTER 11 11.1: Title: ____________________________________________________ 15. Rutherford’s experiments involved bombarded metal foil with _____ _____________. 16. According to Rutherford, the nucleus is composed of positively charged particles called ______________ and neutral particles called _______________________. 17. What did Rutherford suggest about how the electrons were moving? 18. Rutherford was unable to explain why the negative __________________ aren’t attracted into the positive _____________________, causing the atom to collapse. www.thechembook.com Page 6 Learning Guide: 11 LECTURE NOTES Lesson 37: Subatomic particles Text 3.6 We’ll work backwards for a moment, accept there is an atom, and remind you of the three major subatomic particles located in an atom that you learned about in 8th grade. Symbol Location Charge Relative mass Actual mass Electrons e- Outside nucleus Negative 1/1840 9.11 x 10-28 Protons p+ In nucleus Positive 1 1.673 x 10-24 Neutrons n0 In nucleus Neutral 1 1.675 x 10-24 A. Distinguishing Among Atoms 1. Atomic Number, Mass Number, and Electrons a. Atomic Number (Z) i. The number of protons in the nucleus of each atom of that element ii. Atoms are identified by their atomic number iii. Because atoms are neutral, # protons = # electrons iv. Periodic Table is in order of increasing atomic number b. Mass Number (A) i. The total number of protons and neutrons in the nucleus of an isotope c. Electrons i. The volume of an atom is from the area in which the electrons move ii. The chemical properties of an atom arise from the electrons. B. Calculating the number of electrons, protons, and neutrons (Introduction) A = protons + neutrons Z = protons Therefore, to get the number of neutrons, subtract A - Z www.thechembook.com Page 7 Learning Guide: 11 Lesson 38: Dalton’s Atomic Theory Text: 3.3 John Dalton (1766 – 1844) explained observations such as the law of constant composition (a compound always has the same composition) using his atomic theory. The predictive value of the theory led to its eventual acceptance. A. Defining the Atom 1. Atomic Theory a. All matter is made up of very tiny particles called atoms b. Atoms of the same element are chemically alike c. Individual atoms of an element may not all have the same mass. However, the atoms of an element have a definite average mass that is characteristic of the element d. Atoms of different elements have different average masses e. Atoms are not subdivided, created, or destroyed in chemical reactions 1e. Students know the nucleus of the atom is much smaller than the atom yet contains most of its mass. The volume of the hydrogen nucleus is about one trillion times less than the volume of the hydrogen atom, yet the nucleus contains almost all the mass in the form of one proton. The diameter of an atom of any one of the elements is about 10,000 to 100,000 times greater than the diameter of the nucleus. The mass of the atom is densely packed in the nucleus. The electrons occupy a large region of space centered around a tiny nucleus, and so it is this region that defines the volume of the atom. If the nucleus (proton) of a hydrogen atom were as large as the width of a human thumb, the electron would be on the average about one kilometer away in a great expanse of empty space. The electron is almost 2,000 times lighter than the proton; therefore, the large region of space occupied by the electron contains less than 0.1 percent of the mass of the atom. 2. Sizes of Atoms a. Atomic radius i. 40 to 270 picometers (pm) 1. 1 pm = 10-12m ii. Most of the atomic radius is due to the electron cloud b. Nuclear radius i. 0.001 pm ii. density is 2x108 metric tons/cm3 1. 1 metric ton = 1000kg www.thechembook.com Page 8 Learning Guide: 11 B. Models of the Atom A model is a representation of nature, an attempt to communicate an explanation. Scientist Year Model Experiment Focus Democritus ~ 400 B.C.E. None Suggested Atom Dalton 1808 Solid sphere, tiny, indivisible, indestructible particles Weather data Thomson 1897 Plum pudding Cathode Ray Tube; also invented mass spectrometer Electrons Plank 1900 Energy emitted in discrete quantities Radiation from solids Quanta Rutherford 1911 Nuclear Atom; also called the planetary model Gold foil Nucleus Bohr 1913 Bohr Model, electrons travel in discrete orbits Spectrum of Hydrogen Excited and Ground state Einstein 1905 Wave mechanical model Photoelectric Effect Photons Schrödinger 1926 Wave mechanical model Schrödinger cat; thought experiment Schrödinger equation Heisenberg 1929 Wave mechanical model Heisenberg uncertainty principle Murray GellMann; George Zweig 1970s Standard Model Quarks and leptons (matter) * There were many other models developed during this time period but we’ll only focus on these particular ones. www.thechembook.com Page 9 Learning Guide: 11 C. Contributed to the Models of the Atom Maxwell 1873 Visible light consists of electromagnetic waves Planck 1900 Energy emitted in discrete quantities Chadwick 1932 Provides description of light Radiation from solids Quanta; Plank’s constant Identified subatomic particle Neutron Lesson 39: The Structure of the Atom / Thomson’s model Text: 3.5 A. The Electron a. Discovery i. Joseph John Thomson (1897) 1. Cathode ray tube produces a ray with a constant charge to mass ratio 2. All cathode rays are composed of identical negatively charged particles (electrons) B. Plum-pudding model C. Inferences from the properties of electrons i. Atoms are neutral, so there must be positive charges to balance the negatives ii. Electrons have little mass, so atoms must contain other particles that account for most of the mass www.thechembook.com Page 10 Learning Guide: 11 Lesson 40: Rutherford’s model Text 11.1 1a. Students know how to relate the position of an element in the periodic table to its atomic number and atomic mass. An atom consists of a nucleus made of protons and neutrons that is orbited by electrons. The number of protons, not electrons or neutrons, determines the unique properties of an element. This number of protons is called the atomic number. Elements are arranged on the periodic table in order of increasing atomic number. Historically, elements were ordered by atomic mass, but now scientists know that this order would lead to misplaced elements (e.g., tellurium and iodine) because differences in the number of neutrons for isotopes of the same element affect the atomic mass but do not change the identity of the element. D. Structure of the Nucleus 1. The Nucleus a. The Rutherford Experiment (1911) b. Alpha particles (helium nuclei) fired at a thin sheet of gold i. Assumed that the positively charged particles were bounced back if they approached a positively charged atomic nucleus head-on (Like charges repel one another) Results from gold foil experiment 1. Very few particles were greatly deflected back from the gold sheet a. nucleus is very small, dense and positively charged b. most of the atom is empty space 2. Structure of the Nucleus a. Protons i. Positive charge, mass of 1.673x10-27kg ii. The number of protons in the nucleus determines the atom's identity and is called the atomic number (Z) b. Neutrons i. James Chadwick (1932) ii. No charge, mass of 1.675x10-27kg c. Nuclear Forces i. Short range attractive forces: a. neutron-to-neutron, proton-to-proton, www.thechembook.com proton-to-neutron Page 11 Learning Guide: 11 Unanswered Questions What are the electrons doing? How are the electrons arranged? How do electrons move? Why aren’t electrons (negatively charged) attracted to the positive nucleus? Lesson 41: Bohr’s model Text 11.5 The energy of the electrons is restricted to certain discrete values; that is, the energy is quantized. Consider the rungs of a ladder. There is no “in between” on a ladder. Your foot is either on a rung or it is not. The electrons move from each orbital. Photons (packets of light) are either absorbed or released. If it is at the lowest it’s called ground state and the highest is called excited state. Image from http://imagine.gsfc.nasa.gov/docs/teachers/lessons/xray_spectra/background-atoms.html The flame test shows the spectra changes based on the elements. Lesson 42: Wave model Introduction Text 11.6 The Bohr model explained the hydrogen spectrum very well but it failed to explain the spectra of all other atoms. Additional spectra analysis of elements supported a new model of the atom, called the wave model. In this model, orbits do not exist. Instead, orbitals that match spectra are discussed. These orbitals are s (sharp), p (principal), d (diffuse), and f (fundamental). Orbitals do not describe the path or motion of the electron. Instead, they describe the probability of finding an electron at a particular time. www.thechembook.com Page 12 Learning Guide: 11 QUESTIONS AND PROBLEMS 1. How is Thomson’s model of the atom different from Dalton’s model of the atom? Draw a picture of each. 2. How is the Rutherford model different from the previous models? 3. What was wrong with Rutherford’s model of the atom? Why did it need to be modified? www.thechembook.com Page 13 Learning Guide: 11 JOURNAL What points in the material strike you as important? _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ What new material have you learned? _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ List several questions about what you learned? _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ How does what you learned relate to other information that you have learned in this course? _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ How did the class work stimulate your thinking? _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ www.thechembook.com Page 14