DOCSLIB.ORG

LECTURE 23 SPECTROSCOPY and ATOMIC MODELS 29.1 Spectroscopy the Colorful Light from “Neon Signs” 29.2 Atoms Are Due to Atomic Transitions of Various Gas

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
LECTURE 23 SPECTROSCOPY and ATOMIC MODELS 29.1 Spectroscopy the Colorful Light from “Neon Signs” 29.2 Atoms Are Due to Atomic Transitions of Various Gas LECTURE 23 SPECTROSCOPY AND ATOMIC MODELS 29.1 Spectroscopy The colorful light from “neon signs” 29.2 Atoms are due to atomic transitions of various gas. The first nuclear physics experiment Using the nuclear model 29.3 Bohr’s model of atomic quantization 29.4 The Bohr hydrogen atom The stationary states of the hydrogen atom Hydrogen atom energy levels The hydrogen spectrum 29.1 Spectroscopy / demo ! A spectrum is recorded in a spectrometer. ! Self-luminous objects emit a continuous spectrum that depends on the temperature. ! Individual atoms produce atomic spectrum, a discrete spectrum with spectral lines. ! Gases also absorb discrete wavelengths. ! Demo: line spectra Quiz 29.1-1 ! These spectra are from the same element. Which is an emission spectrum, which an absorption spectrum? A. Top is emission; bottom absorption. B. Top is absorption; bottom emission. C. Can’t tell without knowing the element. Quiz 29.1-1 answer ! Top is emission; bottom absorption. ! Every wavelength that is absorbed by the gas is also emitted, but not every emitted wavelength is absorbed. Spectroscopy ! Balmer formula represents the wavelengths of the spectral lines of hydrogen. 91.1 nm ! = 1 1 − () +) ! where ( = 1, 2, 3, … and + can be any integer and + > (. 29.2 Atoms - the raisin-cake model of the atom 6 ! J. J. Thomson, soon after discovering electrons, proposed the raisin-cake model of the atom (“plum-pudding model” actually). ! It was known that electrons are much smaller and less massive than atoms. ! The first observations that atoms have an inner structure came from beta rays and alpha rays emitted from uranium crystal. ! Beta rays are high-speed electrons emitted by uranium. ! Alpha rays (now called alpha particles) consist of helium nuclei, with mass ! = 6.64 ×10)*+ kg, emitted at high speed from a sample. 29.2 The first nuclear physics experiment 7 ! The discovery of large-angle scattering of alpha particles led to the nuclear model of the atom in which negative electrons orbit a small, massive, positive nucleus. ! For fun: Rutherford said “It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.” 29.2 Using the nuclear model 8 ! In the nuclear model, an atom has a nucleus with positively charged protons and neutral neutrons, and negatively charged electrons are orbiting around it. ! Protons and neutrons are both much more massive than electrons. ! Orbiting electrons are very light and can be easily knocked off, creating a positive ion. Quiz: 29.3-1 9 ! Is there something wrong with the nuclear model (like a miniature solar system) of the atom? If so, what is wrong? Choose all that apply. A. No. Everything is fine with the model. B. Yes. Nothing is providing orbiting electrons the centripetal force. C. Yes. Orbiting electrons would collapse into the nucleus in a very short time. D. Yes. The frequency of radiation emitted by an orbiting electron would not agree with the emission spectra. Quiz: 29.3-1 answer 10 ! Yes. Orbiting electrons would collapse into the nucleus in a very short time. ! Yes. The frequency of radiation emitted by an orbiting electron would not agree with the emission spectra. ! The coulomb force by the nucleus is providing orbiting electrons the centripetal force. ! The frequency of radiation emitted by a continuously radiating electron would have a continuous spectrum, rather than the individual frequencies that are actually observed. 29.3 Bohr’s model of atomic quantization 11 ! Bohr model of the atom: ! An electron in an atom can exist only in a stationary state. ! Each stationary state has a discrete well- defined energy. ! An atom can undergo a transition by emitting or absorbing a photon with an energy equal to the difference in the energies of the states: !"#$%$& = !( − !* = ℎ,. ! An atom can be exited by absorbing energy in collision (collisional excitation). Quiz: 29.3-2 ! An atom has the energy levels shown. A photon with a wavelength of 620 nm has an energy of 2.0 eV. Do you expect to see a spectral line with wavelength of 620 nm in this atom’s absorption spectrum? A. Yes B. No C. There’s not enough information to tell. Quiz: 29.3-2 answer ! No ! Absorption occurs from the ground state, in which nearly all the atoms are. ! No quantum jump from the ground state has ∆"#$%& = 2.0 eV. ! Every wavelength that is emitted by gas is not absorbed. Emission transitions Absorption transitions Quiz: 29.3-3 ! An atom has the energy levels shown. A beam of electrons with 5.5 eV kinetic energy collides with a gas of these atoms in the ground state. How many spectral lines will be seen? Quiz: 29.3-3 answer ! An atom has the energy levels shown. A beam of electrons with 5.5 eV kinetic energy collides with a gas of these atoms in the ground state. How many spectral lines will be seen? ! 3 ! A 5.5 eV electron can excite either the ! = 2 or the ! = 3 energy level. Quiz: 29.4-1 16 ! De Broglie showed that the allowed orbits of the Bohr model correspond to standing matter wave of the electrons. What is the relationship between the wavelengths of the electrons in an atom and the circumferences of the allowed orbits? A. The circumference must be an integer multiple of !. " B. The circumference must be an odd integer multiple of . # C. There is not relationship between the circumference and !. Quiz: 29.4-1 answer 17 ! The circumference must be an integer multiple of !. ! The circumference of an allowed orbit is 2#$ = &!, & = 1, 2, 3, ⋯. 29.4 The stationary states of the hydrogen atom 18 ! The allowed radii of the electron’s orbit in a hydrogen atom is % !" = $ &' ! $ = 1, 2, 3, ⋯ ! &' = 0.0529 nm is the Bohr radius. ! The possible orbits are quantized. 29.4 Hydrogen atom energy levels 19 ! There is an energy level in a hydrogen atom corresponding to each allowed state radius. ! 13.6 eV ! = − % = − " &' &' ! & = 1, 2, 3, ⋯ Quiz: 29.4-2 20 ! How much energy in eV does it take to ionize a hydrogen atom in its ground state? Quiz: 29.4-2 answer 21 ! 13.6 eV ! When a hydrogen atom in the ground state absorbs 13.6 eV of energy, the electron makes a transition to ! = ∞ state (ionization limit), which means that the electron is no longer associated to the nucleus. '(.* +, '(.* +, ! $ − $ = − − = 13.6 eV % ' %- '- 29.4 The hydrogen spectrum ! The Bohr hydrogen atom with discrete energy levels correctly predicts the discrete spectrum of the hydrogen atom..
Load more

Recommended publications
  • Pioneers of Atomic Theory Darius Bermudez Discoverers of the Atom
    Pioneers of Atomic Theory Darius Bermudez Discoverers of the Atom Democritus- Greek Philosopher proposed that if something was divided enough times, eventually the particles would be too small to divide any further. Ex: Identify this Greek philosopher who postulated that if an object was divided enough times, there would eventually be small particles that could not be divided any further. Discoverers of the Atom John Dalton- English chemist who made the “billiard ball” atom model. First to prove that rainfall was a result of temperature change. He was the first scientist after Democritus to build on atomic theory. He also created a law on partial pressures. Common Clues: Partial pressures, pioneer of atomic theory, and temperature change causes rainfall. The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. Discoverers of the Atom J.J. Thomson- English Scientist who discovered electrons through a cathode. Made the “plum pudding model” with Lord Kelvin (Kelvin Scale) which stated that negative charges were spread about a positive charged medium, making atoms neutral. Common Clues: Plum pudding, Electrons had negative charges, disproved by either Rutherford or Mardsen and Geiger The image cannot be displayed.
    [Show full text]
  • Lecture #3, Atomic Structure (Rutherford, Bohr Models)
    Welcome to 3.091 Lecture 3 September 14, 2009 Atomic Models: Rutherford & Bohr Periodic Table Quiz 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 Name Grade /10 Image by MIT OpenCourseWare. La Lazy Ce college Pr professors Nd never Pm produce Sm sufficiently Eu educated Gd graduates Tb to Dy dramatically Ho help Er executives Tm trim Yb yearly Lu losses. © source unknown. All rights reserved. This image is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse. La Loony Ce chemistry Pr professor Nd needs Pm partner: Sm seeking cannot be referring Eu educated to 3.091! Gd graduate Tb to must be the “other” Dy develop Ho hazardous chemistry professor Er experiments Tm testing Yb young Lu lab assistants. © source unknown. All rights reserved. This image is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse. 138.9055 920 57 3455 3 6.146 * 1.10 57 5.577 La [Xe]5d16s2 Lanthanum CEase not I to slave, back breaking to tend; PRideless and bootless stoking hearth and fire. No Dream of mine own precious time to spend Pour'ed More to sate your glutt'nous desire.
    [Show full text]
  • Electron Charge Density: a Clue from Quantum Chemistry for Quantum Foundations
    Electron Charge Density: A Clue from Quantum Chemistry for Quantum Foundations Charles T. Sebens California Institute of Technology arXiv v.2 June 24, 2021 Forthcoming in Foundations of Physics Abstract Within quantum chemistry, the electron clouds that surround nuclei in atoms and molecules are sometimes treated as clouds of probability and sometimes as clouds of charge. These two roles, tracing back to Schr¨odingerand Born, are in tension with one another but are not incompatible. Schr¨odinger'sidea that the nucleus of an atom is surrounded by a spread-out electron charge density is supported by a variety of evidence from quantum chemistry, including two methods that are used to determine atomic and molecular structure: the Hartree-Fock method and density functional theory. Taking this evidence as a clue to the foundations of quantum physics, Schr¨odinger'selectron charge density can be incorporated into many different interpretations of quantum mechanics (and extensions of such interpretations to quantum field theory). Contents 1 Introduction2 2 Probability Density and Charge Density3 3 Charge Density in Quantum Chemistry9 3.1 The Hartree-Fock Method . 10 arXiv:2105.11988v2 [quant-ph] 24 Jun 2021 3.2 Density Functional Theory . 20 3.3 Further Evidence . 25 4 Charge Density in Quantum Foundations 26 4.1 GRW Theory . 26 4.2 The Many-Worlds Interpretation . 29 4.3 Bohmian Mechanics and Other Particle Interpretations . 31 4.4 Quantum Field Theory . 33 5 Conclusion 35 1 1 Introduction Despite the massive progress that has been made in physics, the composition of the atom remains unsettled. J. J. Thomson [1] famously advocated a \plum pudding" model where electrons are seen as tiny negative charges inside a sphere of uniformly distributed positive charge (like the raisins|once called \plums"|suspended in a plum pudding).
    [Show full text]
  • Cbiescss05.Pdf
    Science IX Sample Paper 5 Solved www.rava.org.in CLASS IX (2019-20) SCIENCE (CODE 086) SAMPLE PAPER-5 Time : 3 Hours Maximum Marks : 80 General Instructions : (i) The question paper comprises of three sections-A, B and C. Attempt all the sections. (ii) All questions are compulsory. (iii) Internal choice is given in each sections. (iv) All questions in Section A are one-mark questions comprising MCQ, VSA type and assertion-reason type questions. They are to be answered in one word or in one sentence. (v) All questions in Section B are three-mark, short-answer type questions. These are to be answered in about 50-60 words each. (vi) All questions in Section C are five-mark, long-answer type questions. These are to be answered in about 80-90 words each. (vii) This question paper consists of a total of 30 questions. 4. What is the S.I. unit of momentum ? [1] SECTION -A (a) kgms (b) mskg−1 −1 −1 DIRECTION : For question numbers 1 and 2, two statements (c) kgms (d) kg() ms are given- one labelled Assertion (A) and the other labelled Ans : (c) kgms−1 Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below. 5. Which of the following is not a perfectly in elastic collision ? [1] (a) Both A and R are true and R is correct explanation (a) Capture of an electron by proton. of the assertion. (b) Man jumping on to a moving cart. (b) Both A and R are true but R is not the correct explanation of the assertion.
    [Show full text]
  • Coercing Magnetism Into Diamagnetic Ceramics: a Case Study in Alumina Erik Nykwest University of Connecticut - Storrs, [email protected]
    University of Connecticut Masthead Logo OpenCommons@UConn Doctoral Dissertations University of Connecticut Graduate School 4-25-2019 Coercing Magnetism into Diamagnetic Ceramics: A Case Study in Alumina Erik Nykwest University of Connecticut - Storrs, [email protected] Follow this and additional works at: https://opencommons.uconn.edu/dissertations Recommended Citation Nykwest, Erik, "Coercing Magnetism into Diamagnetic Ceramics: A Case Study in Alumina" (2019). Doctoral Dissertations. 2136. https://opencommons.uconn.edu/dissertations/2136 Coercing Magnetism into Diamagnetic Ceramics: A Case Study in Alumina Erik Carl Nykwest, Ph.D. University of Connecticut, 2019 Ceramics are very diverse class of materials whose properties can vary greatly. It is this diversity that make ceramics so useful in advanced technology. The relatively open crystal structure of ceramics makes it pos- sible to impart functionalities via judicious doping. This work focuses on developing a generalized method for introducing magnetism into normally non-magnetic (diamagnetic) ceramics, using the example case of alumina (Al2O3).Here, substitutional doping of Al atoms with 3d transition metal in α- and θ-alumina was studied. Density functional theory was used to predict the structural, electronic, and magnetic properties of doped alumina, as well as its stability. The results show that adding small concentrations of transition metals to alumina may increase magnetic activity by generating unpaired electrons whose net magnetic moments may couple with external magnetic fields. The dopant species and dopant coordination environment are the most important factors in determining the spin density distribution (localized or delocalized from the dopant atom) and net magnetic moment, which strongly direct the ability of the doped alumina to couple with an ex- ternal field.
    [Show full text]
  • Lesson 37: Thomson's Plum Pudding Model
    Lesson 37: Thomson's Plum Pudding Model Remember back in Lesson 18 when we looked at trapping moving particles in a circular path using a magnetic field? • In this lesson we look at how using this type of set up eventually helped physicists start to figure out the nature of the atom. Early Theories about Atoms In 1803 John Dalton presented his theory that the elements of the periodic table were made of atoms. • The main reason he was proposing this idea was to be able to explain the chemistry that he was studying. • Dalton believed that atoms were solid pieces of matter that could not be broken down any further. ◦ This is why his model is often referred to as the Solid Sphere Model. • Although Dalton's model was able to explain the way he saw chemical reactions working, he was unable to really prove that matter was made up of these atoms, or how chemical bonding could happen between them. During the late 1800's experiments with cathode ray tubes (CRTs) were starting to The negative give the first glimpses into what an atom might be. electrode is referred ● A cathode ray tube is just a vacuum tube with two electrodes at the ends. to as the cathode. That's the reason ○ When a really high voltage is applied, mysterious “cathode rays” this is called a moved from the negative electrode to the positive electrode. cathode ray tube. ○ Sometimes you could see a glow at the opposite end of the tube when the tube was turned on. ● William Crookes used a really high quality cathode ray tube in 1885.
    [Show full text]
  • First-Principles Density Functional Theory Studies on Perovskite Materials
    New Jersey Institute of Technology Digital Commons @ NJIT Dissertations Electronic Theses and Dissertations 5-31-2021 First-principles density functional theory studies on perovskite materials Aneer Lamichhane New Jersey Institute of Technology Follow this and additional works at: https://digitalcommons.njit.edu/dissertations Part of the Condensed Matter Physics Commons, and the Materials Science and Engineering Commons Recommended Citation Lamichhane, Aneer, "First-principles density functional theory studies on perovskite materials" (2021). Dissertations. 1518. https://digitalcommons.njit.edu/dissertations/1518 This Dissertation is brought to you for free and open access by the Electronic Theses and Dissertations at Digital Commons @ NJIT. It has been accepted for inclusion in Dissertations by an authorized administrator of Digital Commons @ NJIT. For more information, please contact [email protected]. Copyright Warning & Restrictions The copyright law of the United States (Title 17, United States Code) governs the making of photocopies or other reproductions of copyrighted material. Under certain conditions specified in the law, libraries and archives are authorized to furnish a photocopy or other reproduction. One of these specified conditions is that the photocopy or reproduction is not to be “used for any purpose other than private study, scholarship, or research.” If a, user makes a request for, or later uses, a photocopy or reproduction for purposes in excess of “fair use” that user may be liable for copyright infringement,
    [Show full text]
  • Basic Properties of Atoms Emission Spectral Lines
    Atomic Models The purpose of this chapter is to build a simplest atomic model that will help us to understand the structure of atom. This is attained by referring to some basic experimental facts that have been gathered since 1900’s (e.g. Rutherford scattering experiment, atomic spectral lines etc.) For this we need to explore the wave nature of electron. Basic properties of atoms 1) Atoms are of microscopic size, ~ 10−10 m. Visible light is not enough to resolve (see) the detail structure of an atom as its size is only of the order of 100 nm. 2) Atoms are stable. The force (EM force) that hold an atom together is attractive. 3) Atoms contain negatively charges (e.g. as seen in Compton and photoelectric effect), electrons, but are electrically neutral. An atom with Z electrons must also contain a net positive charge of +Ze. 4) Atoms emit and absorb EM radiation (because of this, EM wave is usually used to probe the structure of an atom). Emission spectral lines A single atom or molecule which rarely interacts with other molecules (such as a gas in a tube with very diluted concentration) emit radiation characteristic of the particular atom/molecule species. This happen when the atoms/molecules are ``excited’’ e.g. by heating or passing electric current through it The emitted radiation displays characteristic discrete sets of spectrum which contains certain specific wavelengths only. The spectral lines are analysed with spectrometer, which give important physical information of the atom/molecules by analysing the wavelengths composition and pattern of these lines.
    [Show full text]
  • Atomic Models
    Atomic Models Article to be checked Check of this article is requested. Suggested reviewer: RNDr. Petr Heřman Atomic models There has been a variety of atomic models throughout history of atomic physics, that refers mainly to a period from the beginning of 19th century to the first half of 20th century, when a final model of atom which is being used nowadays (or accepted as the most accurate one) was invented. Although the awareness of atom existence goes way back to the antique period of the world history (Greek conception of atom), this article will be mainly about five basic atomic models, from which each one has somehow contributed to how we percept the structure of atom itself - Dalton´s Billiard Ball Model, J.J Thomson's "plum pudding" model, Rutherford's Planetary model, Bohr's Atomic model, Electron Cloud Model/Quantum Mechanics Model. John Dalton’s atomic model John Dalton was an English scientist, who came up with an idea that all matter is composed of very small things. It was the first complete attempt to describe all matter in terms of particles. He called these particles atoms and formed an atomic theory. In this theory he claims that: All matter is made of atoms. Atoms are indivisible and indestructible All atoms of a given element are identical in mass and properties Compounds are formed by a combination of two or more different kinds of atoms A chemical reaction is a rearrangement of atoms Parts of his theory had to be modified based on the discovery of subatomic particles and isotopes.
    [Show full text]
  • Section 28-2: Models of the Atom
    Answer to Essential Question 28.1: (a) In general, four energy levels give six photon energies. One way to count these is to start with the highest level, –12 eV. An electron starting in the –12 eV level can drop to any of the other three levels, giving three different photon energies. An electron starting at the –15 eV level can drop to either of the two lower levels, giving two more photon energies. Finally, an electron can drop from the –21 eV level to the –31 eV level, giving one more photon energy (for a total of six). (b) The minimum photon energy corresponds to the 3 eV difference between the –12 eV level and the –15 eV level. The maximum photon energy corresponds to the 19 eV difference between the –12 eV level and the –31 eV level. 28-2 Models of the Atom It is amazing to think about how far we have come, in terms of our understanding of the physical world, in the last century or so. A good example of our progress is how much our model of the atom has evolved. Let’s spend some time discussing the evolution of atomic models. Ernest Rutherford probes the plum-pudding model J. J. Thomson, who discovered the electron in 1897, proposed a plum-pudding model of the atom. In this model, electrons were thought to be embedded in a ball of positive charge, like raisins are embedded in a plum pudding. Ernest Rutherford (1871 - 1937) put this model to the test by designing an experiment that involved firing alpha particles (helium nuclei) at a very thin film of gold.
    [Show full text]
  • Of 67 the Diagrams Show Two Different Models of an Atom. 'Plum Pudding'
    Q1. The diagrams show two different models of an atom. ‘Plum pudding’ model Model used today (a) The particles labelled ‘Xߣ in the plum pudding model are also included in the model of the atom used today. What are the particles labelled ‘X’ ? _________________________ (1) (b) Scientists decided that the ‘plum pudding’ model was wrong and needed replacing. Which one of the following statements gives a reason for deciding that a scientific model needs replacing? Tick ( ) one box. The model is too simple. The model has been used by scientists for a long time. The model cannot explain the results from a new experiment. (1) (c) The table gives information about the three types of particle that are in the model of the atom used today. Page 1 of 67 Particle Relative mass Relative charge 1 +1 very small –1 1 0 Complete the table by adding the names of the particles. (2) (Total 4 marks) Q2. (a) The diagram represents an atom of beryllium. Use words from the box to label the diagram. electron ion isotope molecule nucleus (2) (b) Use crosses (x) to complete the diagram to show the electronic structure of a magnesium atom. The atomic (proton) number of magnesium is 12. (2) (Total 4 marks) Page 2 of 67 Q3. The diagram represents an atom. Choose words from the list to label the diagram. electron ion neutron nucleus (Total 3 marks) Q4. About 100 years ago a scientist called J. J. Thomson thought that an atom was a ball of positive charge with negative particles stuck inside.
    [Show full text]
  • Lecture 36 (Atomic Spectra)
    Lecture 36 (Atomic Spectra) Physics 2310-01 Spring 2020 Douglas Fields Fraunhofer Lines • In the late 1700s and early 1800s, one of the premier skills was that of glassmaker. Joseph Fraunhofer became one of the most skilled and sought after glassmakers. • He discovered a large set of missing colors in the solar spectrum while looking for a bright line instead. Thus in 1814, Fraunhofer invented the spectroscope. In the course of his experiments he discovered the bright fixed line which appears in the orange color of the spectrum when it is produced by the light of fire. This line enabled him afterward to determine the absolute power of refraction in different substances. Experiments to ascertain whether the solar spectrum contained the same bright line in the orange as that produced by the light of fire led him to the discovery of 574 dark fixed lines in the solar spectrum; millions of such fixed absorption lines are now known. - Wikipedia He missed a few… Emission Lines • About the same time, people were using flame emission spectroscopy to see that different materials emitted light of specific frequencies when heated to high enough temperatures that they became heated gases. Emission Lines • Another way to do this is to pass an electric current through a gas, thermally heating it and seeing the spectra of light emission using a diffraction grating. Absorption & Emission • The other aspect that was noticed is that spectra emitted by an heated element was the same as the spectra of absorption when continuous light was passed through the same cool element (as a gas).
    [Show full text]