1 OpenStax-CNX module: m Bohr's Theory of the Hydrogen Atom OpenStax College This work is produced by OpenStax-CNX and licensed under the Creative Commons Attribution License 4.0 Abstract Describe the mysteries of atomic spectra. Explain Bohr's theory of the hydrogen atom. Explain Bohr's planetary model of the atom. Illustrate energy state using the energy-level diagram. Describe the triumphs and limits of Bohr's theory. The great Danish physicist Niels Bohr ( ) made immediate use of Rutherford's planetary model of the atom. (Figure 1). Bohr became convinced of its validity and spent part of 1912 at Rutherford's laboratory. In 1913, after returning to Copenhagen, he began publishing his theory of the simplest atom, hydrogen, based on the planetary model of the atom. For decades, many questions had been asked about atomic characteristics. From their sizes to their spectra, much was known about atoms, but little had been explained in terms of the laws of physics. Bohr's theory explained the atomic spectrum of hydrogen and established new and broadly applicable principles in quantum mechanics. Version 1.6: Jul 15, :01 am
2 OpenStax-CNX module: m Figure 1: Niels Bohr, Danish physicist, used the planetary model of the atom to explain the atomic spectrum and size of the hydrogen atom. His many contributions to the development of atomic physics and quantum mechanics, his personal inuence on many students and colleagues, and his personal integrity, especially in the face of Nazi oppression, earned him a prominent place in history. (credit: Unknown Author, via Wikimedia Commons) 1 Mysteries of Atomic Spectra As noted in Quantization of Energy 1, the energies of some small systems are quantized. Atomic and molecular emission and absorption spectra have been known for over a century to be discrete (or quantized). (See Figure 2.) Maxwell and others had realized that there must be a connection between the spectrum of an atom and its structure, something like the resonant frequencies of musical instruments. But, in spite of years of eorts by many great minds, no one had a workable theory. (It was a running joke that any theory of atomic and molecular spectra could be destroyed by throwing a book of data at it, so complex were the spectra.) Following Einstein's proposal of photons with quantized energies directly proportional to their wavelengths, it became even more evident that electrons in atoms can exist only in discrete orbits. 1 "Quantization of Energy" <
3 OpenStax-CNX module: m Figure 2: Part (a) shows, from left to right, a discharge tube, slit, and diraction grating producing a line spectrum. Part (b) shows the emission line spectrum for iron. The discrete lines imply quantized energy states for the atoms that produce them. The line spectrum for each element is unique, providing a powerful and much used analytical tool, and many line spectra were well known for many years before they could be explained with physics. (credit for (b): Yttrium91, Wikimedia Commons) In some cases, it had been possible to devise formulas that described the emission spectra. As you might expect, the simplest atomhydrogen, with its single electronhas a relatively simple spectrum. The hydrogen spectrum had been observed in the infrared (IR), visible, and ultraviolet (UV), and several series of spectral lines had been observed. (See Figure 3.) These series are named after early researchers who studied them in particular depth. The observed hydrogen-spectrum wavelengths can be calculated using the following formula: ( 1 1 λ = R 1 ) n 2, (1) i n 2 f where λ is the wavelength of the emitted EM radiation and R is the Rydberg constant, determined by the experiment to be R = /m ( or m 1). (2) The constant n f is a positive integer associated with a specic series. For the Lyman series, n f = 1; for the Balmer series, n f = 2; for the Paschen series, n f = 3; and so on. The Lyman series is entirely in the UV, while part of the Balmer series is visible with the remainder UV. The Paschen series and all the rest are entirely IR. There are apparently an unlimited number of series, although they lie progressively farther into the infrared and become dicult to observe as n f increases. The constant n i is a positive integer, but it must be greater than n f. Thus, for the Balmer series, n f = 2 and n i = 3, 4, 5, 6,... Note that n i can approach
4 OpenStax-CNX module: m innity. While the formula in the wavelengths equation was just a recipe designed to t data and was not based on physical principles, it did imply a deeper meaning. Balmer rst devised the formula for his series alone, and it was later found to describe all the other series by using dierent values of n f. Bohr was the rst to comprehend the deeper meaning. Again, we see the interplay between experiment and theory in physics. Experimentally, the spectra were well established, an equation was found to t the experimental data, but the theoretical foundation was missing. Figure 3: A schematic of the hydrogen spectrum shows several series named for those who contributed most to their determination. Part of the Balmer series is in the visible spectrum, while the Lyman series is entirely in the UV, and the Paschen series and others are in the IR. Values of n f and n i are shown for some of the lines. Example 1: Calculating Wave Interference of a Hydrogen Line What is the distance between the slits of a grating that produces a rst-order maximum for the second Balmer line at an angle of 15º? Strategy and Concept For an Integrated Concept problem, we must rst identify the physical principles involved. In this example, we need to know (a) the wavelength of light as well as (b) conditions for an interference maximum for the pattern from a double slit. Part (a) deals with a topic of the present chapter, while part (b) considers the wave interference material of Wave Optics 2. Solution for (a) Hydrogen spectrum wavelength. The Balmer series requires that n f = 2. The rst line in the series is taken to be for n i = 3, and so the second would have n i = 4. The calculation is a straightforward application of the wavelength equation. Entering the determined values for n f and n i yields 1 λ = R ( 1 n 2 f 1 n 2 i ) = ( m 1) ( ) = m 1. (3) 2 "Introduction to Wave Optics" <
5 OpenStax-CNX module: m Inverting to nd λ gives λ = m 1 = m = 486 nm. Discussion for (a) This is indeed the experimentally observed wavelength, corresponding to the second (blue-green) line in the Balmer series. More impressive is the fact that the same simple recipe predicts all of the hydrogen spectrum lines, including new ones observed in subsequent experiments. What is nature telling us? Solution for (b) Double-slit interference (Wave Optics 3 ). To obtain constructive interference for a double slit, the path length dierence from two slits must be an integral multiple of the wavelength. This condition was expressed by the equation (4) d sin θ = mλ, (5) where d is the distance between slits and θ is the angle from the original direction of the beam. The number m is the order of the interference; m = 1 in this example. Solving for d and entering known values yields (1) (486 nm) d = = m. (6) sin 15º Discussion for (b) This number is similar to those used in the interference examples of Introduction to Quantum Physics 4 (and is close to the spacing between slits in commonly used diraction glasses). 2 Bohr's Solution for Hydrogen Bohr was able to derive the formula for the hydrogen spectrum using basic physics, the planetary model of the atom, and some very important new proposals. His rst proposal is that only certain orbits are allowed: we say that the orbits of electrons in atoms are quantized. Each orbit has a dierent energy, and electrons can move to a higher orbit by absorbing energy and drop to a lower orbit by emitting energy. If the orbits are quantized, the amount of energy absorbed or emitted is also quantized, producing discrete spectra. Photon absorption and emission are among the primary methods of transferring energy into and out of atoms. The energies of the photons are quantized, and their energy is explained as being equal to the change in energy of the electron when it moves from one orbit to another. In equation form, this is E = hf = E i E f. (7) Here, E is the change in energy between the initial and nal orbits, and hf is the energy of the absorbed or emitted photon. It is quite logical (that is, expected from our everyday experience) that energy is involved in changing orbits. A blast of energy is required for the space shuttle, for example, to climb to a higher orbit. What is not expected is that atomic orbits should be quantized. This is not observed for satellites or planets, which can have any orbit given the proper energy. (See Figure 4.) 3 "Introduction to Wave Optics" < 4 "Introduction to Quantum Physics" <
6 OpenStax-CNX module: m Figure 4: The planetary model of the atom, as modied by Bohr, has the orbits of the electrons quantized. Only certain orbits are allowed, explaining why atomic spectra are discrete (quantized). The energy carried away from an atom by a photon comes from the electron dropping from one allowed orbit to another and is thus quantized. This is likewise true for atomic absorption of photons. Figure 5 shows an energy-level diagram, a convenient way to display energy states. In the present discussion, we take these to be the allowed energy levels of the electron. Energy is plotted vertically with the lowest or ground state at the bottom and with excited states above. Given the energies of the lines in an atomic spectrum, it is possible (although sometimes very dicult) to determine the energy levels of an atom. Energy-level diagrams are used for many systems, including molecules and nuclei. A theory of the atom or any other system must predict its energies based on the physics of the system.
7 OpenStax-CNX module: m Figure 5: An energy-level diagram plots energy vertically and is useful in visualizing the energy states of a system and the transitions between them. This diagram is for the hydrogen-atom electrons, showing a transition between two orbits having energies E 4 and E 2. Bohr was clever enough to nd a way to calculate the electron orbital energies in hydrogen. This was an important rst step that has been improved upon, but it is well worth repeating here, because it does correctly describe many characteristics of hydrogen. Assuming circular orbits, Bohr proposed that the angular momentum L of an electron in its orbit is quantized, that is, it has only specic, discrete values. The value for L is given by the formula L = m e vr n = n h (n = 1, 2, 3,... ), (8) 2π where L is the angular momentum, m e is the electron's mass, r n is the radius of the n th orbit, and h is Planck's constant. Note that angular momentum is L = Iω. For a small object at a radius r, I = mr 2 and ω = v/r, so that L = ( mr 2) (v/r) = mvr. Quantization says that this value of mvr can only be equal to h/2, 2h/2, 3h/2, etc. At the time, Bohr himself did not know why angular momentum should be quantized, but using this assumption he was able to calculate the energies in the hydrogen spectrum, something no one else had done at the time. From Bohr's assumptions, we will now derive a number of important properties of the hydrogen atom from the classical physics we have covered in the text. We start by noting the centripetal force causing the electron to follow a circular path is supplied by the Coulomb force. To be more general, we note that this analysis is valid for any single-electron atom. So, if a nucleus has Z protons (Z = 1 for hydrogen, 2 for helium,
8 OpenStax-CNX module: m etc.) and only one electron, that atom is called a hydrogen-like atom. The spectra of hydrogen-like ions are similar to hydrogen, but shifted to higher energy by the greater attractive force between the electron and nucleus. The magnitude of the centripetal force is m e v 2 /r n, while the Coulomb force is k (Zq e ) (q e ) /r 2 n. The tacit assumption here is that the nucleus is more massive than the stationary electron, and the electron orbits about it. This is consistent with the planetary model of the atom. Equating these, k Zq2 e r 2 n = m ev 2 r n (Coulomb = centripetal). (9) Angular momentum quantization is stated in an earlier equation. We solve that equation for v, substitute it into the above, and rearrange the expression to obtain the radius of the orbit. This yields: r n = n2 Z a B, for allowed orbits (n = 1, 2, 3,... ), (10) where a B is dened to be the Bohr radius, since for the lowest orbit (n = 1) and for hydrogen (Z = 1), r 1 = a B. It is left for this chapter's Problems and Exercises to show that the Bohr radius is h 2 a B = 4π 2 m e kq 2 = m. (11) e These last two equations can be used to calculate the radii of the allowed (quantized) electron orbits in any hydrogen-like atom. It is impressive that the formula gives the correct size of hydrogen, which is measured experimentally to be very close to the Bohr radius. The earlier equation also tells us that the orbital radius is proportional to n 2, as illustrated in Figure 6.
9 OpenStax-CNX module: m Figure 6: The allowed electron orbits in hydrogen have the radii shown. These radii were rst calculated by Bohr and are given by the equation r n = n2 ab. The lowest orbit has the experimentally veried Z diameter of a hydrogen atom. To get the electron orbital energies, we start by noting that the electron energy is the sum of its kinetic and potential energy: E n = KE + PE. (12) Kinetic energy is the familiar KE = (1/2) m e v 2, assuming the electron is not moving at relativistic speeds. Potential energy for the electron is electrical, or PE = q e V, where V is the potential due to the nucleus, which looks like a point charge. The nucleus has a positive charge Zq e ; thus, V = kzq e /r n, recalling an earlier equation for the potential due to a point charge. Since the electron's charge is negative, we see that PE = kzq e /r n. Entering the expressions for KE and PE, we nd E n = 1 2 m ev 2 k Zq2 e r n. (13) Now we substitute r n and v from earlier equations into the above expression for energy. Algebraic manipulation yields E n = Z2 n 2 E 0 (n = 1, 2, 3,...) (14)
10 OpenStax-CNX module: m for the orbital energies of hydrogen-like atoms. Here, E 0 is the ground-state energy (n = 1) for hydrogen (Z = 1) and is given by Thus, for hydrogen, E 0 = 2π2 q 4 em e k 2 h 2 = 13.6 ev. (15) 13.6 ev E n = n 2 (n = 1, 2, 3,...). (16) Figure 7 shows an energy-level diagram for hydrogen that also illustrates how the various spectral series for hydrogen are related to transitions between energy levels.
11 OpenStax-CNX module: m Figure 7: Energy-level diagram for hydrogen showing the Lyman, Balmer, and Paschen series of transitions. The orbital energies are calculated using the above equation, rst derived by Bohr. Electron total energies are negative, since the electron is bound to the nucleus, analogous to being in a hole without enough kinetic energy to escape. As n approaches innity, the total energy becomes zero. This corresponds to a free electron with no kinetic energy, since r n gets very large for large n, and the electric potential energy thus becomes zero. Thus, 13.6 ev is needed to ionize hydrogen (to go from 13.6 ev to 0, or unbound), an experimentally veried number. Given more energy, the electron becomes unbound with some kinetic energy. For example, giving 15.0 ev to an electron in the ground state of hydrogen strips it from the atom and leaves it with 1.4 ev of kinetic energy.
12 OpenStax-CNX module: m Finally, let us consider the energy of a photon emitted in a downward transition, given by the equation to be Substituting E n = ( 13.6 ev/n 2), we see that ( 1 hf = (13.6 ev) 1 n 2 i E = hf = E i E f. (17) n 2 f ). (18) Dividing both sides of this equation by hc gives an expression for 1/λ: hf hc = f c = 1 ( (13.6 ev) 1 = 1 ) λ hc n 2. (19) i It can be shown that ( ) 13.6 ev (13.6 ev) ( J/eV ) = ( hc J s ) ( m/s ) = m 1 = R (20) is the Rydberg constant. Thus, we have used Bohr's assumptions to derive the formula rst proposed by Balmer years earlier as a recipe to t experimental data. ( 1 1 λ = R 1 ) n 2 (21) i n 2 f We see that Bohr's theory of the hydrogen atom answers the question as to why this previously known formula describes the hydrogen spectrum. It is because the energy levels are proportional to 1/n 2, where n is a non-negative integer. A downward transition releases energy, and so n i must be greater than n f. The various series are those where the transitions end on a certain level. For the Lyman series, n f = 1 that is, all the transitions end in the ground state (see also Figure 7). For the Balmer series, n f = 2, or all the transitions end in the rst excited state; and so on. What was once a recipe is now based in physics, and something new is emergingangular momentum is quantized. 3 Triumphs and Limits of the Bohr Theory Bohr did what no one had been able to do before. Not only did he explain the spectrum of hydrogen, he correctly calculated the size of the atom from basic physics. Some of his ideas are broadly applicable. Electron orbital energies are quantized in all atoms and molecules. Angular momentum is quantized. The electrons do not spiral into the nucleus, as expected classically (accelerated charges radiate, so that the electron orbits classically would decay quickly, and the electrons would sit on the nucleusmatter would collapse). These are major triumphs. But there are limits to Bohr's theory. It cannot be applied to multielectron atoms, even one as simple as a two-electron helium atom. Bohr's model is what we call semiclassical. The orbits are quantized (nonclassical) but are assumed to be simple circular paths (classical). As quantum mechanics was developed, it became clear that there are no well-dened orbits; rather, there are clouds of probability. Bohr's theory also did not explain that some spectral lines are doublets (split into two) when examined closely. We shall examine many of these aspects of quantum mechanics in more detail, but it should be kept in mind that Bohr did not fail. Rather, he made very important steps along the path to greater knowledge and laid the foundation for all of atomic physics that has since evolved. : How did scientists gure out the structure of atoms without looking at them? Try out dierent models by shooting light at the atom. Check how the prediction of the model matches the experimental results. n 2 f
13 OpenStax-CNX module: m Figure 8: Models of the Hydrogen Atom 5 4 Section Summary The planetary model of the atom pictures electrons orbiting the nucleus in the way that planets orbit the sun. Bohr used the planetary model to develop the rst reasonable theory of hydrogen, the simplest atom. Atomic and molecular spectra are quantized, with hydrogen spectrum wavelengths given by the formula ( 1 1 λ = R n 2 f 1 n 2 i ), (22) where λ is the wavelength of the emitted EM radiation and R is the Rydberg constant, which has the value R = m 1. (23) The constants n i and n f are positive integers, and n i must be greater than n f. Bohr correctly proposed that the energy and radii of the orbits of electrons in atoms are quantized, with energy for transitions between orbits given by E = hf = E i E f, (24) where E is the change in energy between the initial and nal orbits and hf is the energy of an absorbed or emitted photon. It is useful to plot orbital energies on a vertical graph called an energylevel diagram. Bohr proposed that the allowed orbits are circular and must have quantized orbital angular momentum given by L = m e vr n = n h (n = 1, 2, 3...), (25) 2π where L is the angular momentum, r n is the radius of the nth orbit, and h is Planck's constant. For all one-electron (hydrogen-like) atoms, the radius of an orbit is given by r n = n2 Z a B (allowed orbits n = 1, 2, 3,...), (26) Z is the atomic number of an element (the number of electrons is has when neutral) and a B is dened to be the Bohr radius, which is h 2 a B = 4π 2 m e kq 2 e = m. (27) 5
14 OpenStax-CNX module: m Furthermore, the energies of hydrogen-like atoms are given by where E0 is the ground-state energy and is given by E n = Z2 n 2 E 0 (n = 1, 2, 3...), (28) E 0 = 2π2 q 4 em e k 2 h 2 = 13.6 ev. (29) Thus, for hydrogen, 13.6 ev E n = n 2 (n, =, 1, 2, 3...). (30) The Bohr Theory gives accurate values for the energy levels in hydrogen-like atoms, but it has been improved upon in several respects. 5 Conceptual Questions Exercise 1 How do the allowed orbits for electrons in atoms dier from the allowed orbits for planets around the sun? Explain how the correspondence principle applies here. Exercise 2 Explain how Bohr's rule for the quantization of electron orbital angular momentum diers from the actual rule. Exercise 3 What is a hydrogen-like atom, and how are the energies and radii of its electron orbits related to those in hydrogen? 6 Problems & Exercises Exercise 4 (Solution on p. 16.) By calculating its wavelength, show that the rst line in the Lyman series is UV radiation. Exercise 5 Find the wavelength of the third line in the Lyman series, and identify the type of EM radiation. Exercise 6 (Solution on p. 16.) Look up the values of the quantities in a B = h 2 4π 2 m ekq, and verify that the Bohr radius a 2 B is e m. Exercise 7 Verify that the ground state energy E 0 is 13.6 ev by using E 0 = 2π2 q 4 e mek2 h. 2 Exercise 8 (Solution on p. 16.) If a hydrogen atom has its electron in the n = 4 state, how much energy in ev is needed to ionize it? Exercise 9 A hydrogen atom in an excited state can be ionized with less energy than when it is in its ground state. What is n for a hydrogen atom if ev of energy can ionize it? Exercise 10 (Solution on p. 16.) Find the radius of a hydrogen atom in the n = 2 state according to Bohr's theory.
15 OpenStax-CNX module: m Exercise 11 Show that (13.6eV ) /hc = m = R (Rydberg's constant), as discussed in the text. Exercise 12 (Solution on p. 16.) What is the smallest-wavelength line in the Balmer series? Is it in the visible part of the spectrum? Exercise 13 Show that the entire Paschen series is in the infrared part of the spectrum. To do this, you only need to calculate the shortest wavelength in the series. Exercise 14 (Solution on p. 16.) Do the Balmer and Lyman series overlap? To answer this, calculate the shortest-wavelength Balmer line and the longest-wavelength Lyman line. Exercise 15 (a) Which line in the Balmer series is the rst one in the UV part of the spectrum? (b) How many Balmer series lines are in the visible part of the spectrum? (c) How many are in the UV? Exercise 16 (Solution on p. 16.) A wavelength of µm is observed in a hydrogen spectrum for a transition that ends in the n f = 5 level. What was n i for the initial level of the electron? Exercise 17 A singly ionized helium ion has only one electron and is denoted He +. What is the ion's radius in the ground state compared to the Bohr radius of hydrogen atom? Exercise 18 (Solution on p. 16.) A beryllium ion with a single electron (denoted Be 3+ ) is in an excited state with radius the same as that of the ground state of hydrogen. (a) What is n for the Be 3+ ion? (b) How much energy in ev is needed to ionize the ion from this excited state? Exercise 19 Atoms can be ionized by thermal collisions, such as at the high temperatures found in the solar corona. One such ion is C +5, a carbon atom with only a single electron. (a) By what factor are the energies of its hydrogen-like levels greater than those of hydrogen? (b) What is the wavelength of the rst line in this ion's Paschen series? (c) What type of EM radiation is this? Exercise 20 (Solution on p. 16.) Verify Equations r n = n2 Z a h B and a B = 2 4π 2 m ekq = m using the approach stated 2 e in the text. That is, equate the Coulomb and centripetal forces and then insert an expression for velocity from the condition for angular momentum quantization. Exercise 21 The wavelength of the four Balmer series lines for hydrogen are found to be 410.3, 434.2, 486.3, and nm. What average ( percentage ) dierence is found between these wavelength numbers and those predicted by 1 λ = R 1? It is amazing how well a simple formula (disconnected n 2 f 1 n 2 i originally from theory) could duplicate this phenomenon.
16 OpenStax-CNX module: m Solutions to Exercises in this Module Solution ( to Exercise ) (p. 14) [ ] 1 λ = R 1 1 λ = 1 (ni n f ) 2 n 2 n 2 R ; n n 2 i = 2, n f = 1, so that n2 f i i f ( ) [ ] m λ = (2 1) = m = 122 nm, which is UV radiation. 2 Solution to Exercise (p. 14) h a B = 2 4π 2 m ekzq = 2 e Solution to Exercise (p. 14) ev Solution to Exercise (p. 14) m Solution to Exercise (p. 15) 365 nm It is in the ultraviolet. Solution to Exercise (p. 15) No overlap 365 nm 122 nm Solution to Exercise (p. 15) 7 Solution to Exercise (p. 15) (a) 2 (b) 54.4 ev Solution to Exercise (p. 15) kzq 2 e r 2 n = mev 2 r n ( J s) 2 4π 2 ( kg)( N m 2 /C 2 )(1)( C), so that r n = kzq2 e m ev 2 velocity, giving: r n = kzq2 e m e Glossary 4π2 m 2 e r2 n n 2 h 2 = kzq2 e m e 1 V 2. From the equation m e vr n = n h 2π so that r n = n2 Z 2 = m h 2 4π 2 m ekq = n2 2 e Z a h B, where a B = 2 4π 2 m ekq. 2 e, we can substitute for the Denition 1: hydrogen spectrum wavelengths ( ) the wavelengths of visible light from hydrogen; can be calculated by 1 λ = R 1 1 n 2 n 2 f i Denition 2: Rydberg constant a physical constant related to the atomic spectra with an established value of m 1 Denition 3: double-slit interference an experiment in which waves or particles from a single source impinge upon two slits so that the resulting interference pattern may be observed Denition 4: energy-level diagram a diagram used to analyze the energy level of electrons in the orbits of an atom Denition 5: Bohr radius the mean radius of the orbit of an electron around the nucleus of a hydrogen atom in its ground state Denition 6: hydrogen-like atom any atom with only a single electron Denition 7: energies of hydrogen-like atoms Z Bohr formula for energies of electron states in hydrogen-like atoms: E n = 2 n E 2 0 ( n = 1, 2, 3,
Review of the isotope effect in the hydrogen spectrum 1 Balmer and Rydberg Formulas By the middle of the 19th century it was well established that atoms emitted light at discrete wavelengths. This is in
Experiment #12: The Bohr Atom Purpose: To observe the visible spectrum of hydrogen and helium and verify the Bohr model of the hydrogen atom. Equipment: Spectroscope Hydrogen and Helium Gas Discharge Tubes,
ConcepTest 27.1 Photons Which has more energy, a photon of: 1) red light 2) yellow light 3) green light 4) blue light 5) all have the same energy 400 nm 500 nm 600 nm 700 nm ConcepTest 27.1 Photons Which
Atoms Absorb & Emit Light Spectra The wavelength of the light that an element emits or absorbs is its fingerprint. Atoms emit and absorb light First Test is Thurs, Feb 1 st About 30 multiple choice questions
TIME OF COMPLETION NAME SOLUTION DEPARTMENT OF NATURAL SCIENCES PHYS 3650, Exam 2 Section 1 Version 1 October 31, 2005 Total Weight: 100 points 1. Check your examination for completeness prior to starting.
Chapter 18: The Structure of the Atom 1. For most elements, an atom has A. no neutrons in the nucleus. B. more protons than electrons. C. less neutrons than electrons. D. just as many electrons as protons.
Atomic Structure: Chapter Problems Bohr Model Class Work 1. Describe the nuclear model of the atom. 2. Explain the problems with the nuclear model of the atom. 3. According to Niels Bohr, what does n stand
Wave Function, ψ Chapter 28 Atomic Physics The Hydrogen Atom The Bohr Model Electron Waves in the Atom The value of Ψ 2 for a particular object at a certain place and time is proportional to the probability
Electron Orbits In an atom model in which negatively charged electrons move around a small positively charged nucleus stable orbits are possible. Consider the simple example of an atom with a nucleus of
THE BOHR QUANTUM MODEL INTRODUCTION When light from a low-pressure gas is subject to an electric discharge, a discrete line spectrum is emitted. When light from such a low-pressure gas is examined with
The Nature of Light Light and other forms of radiation carry information to us from distance astronomical objects Visible light is a subset of a huge spectrum of electromagnetic radiation Maxwell pioneered
The Photoelectric Effect. The Wave particle duality of light Light, like any other E.M.R (electromagnetic radiation) has got a dual nature. That is there are experiments that prove that it is made up of
From lowest energy to highest energy, which of the following correctly orders the different categories of electromagnetic radiation? From lowest energy to highest energy, which of the following correctly
WAVES AND ELECTROMAGNETIC RADIATION All waves are characterized by their wavelength, frequency and speed. Wavelength (lambda, ): the distance between any 2 successive crests or troughs. Frequency (nu,):
5. The Nature of Light Light travels in vacuum at 3.0. 10 8 m/s Light is one form of electromagnetic radiation Continuous radiation: Based on temperature Wien s Law & the Stefan-Boltzmann Law Light has
Atomic Structure Ron Robertson r2 n:\files\courses\1110-20\2010 possible slides for web\atomicstructuretrans.doc I. What is Light? Debate in 1600's: Since waves or particles can transfer energy, what is
Physics 111 Homework Solutions Week #9 - Tuesday Friday, February 25, 2011 Chapter 22 Questions - None Multiple-Choice 223 A 224 C 225 B 226 B 227 B 229 D Problems 227 In this double slit experiment we
614 Chapter 28 Atomic Physics GOALS After you have mastered the contents of this chapter, you will be able to achieve the following goals: Definitions Define each of the following terms and use it in an
AP* Atomic Structure & Periodicity ree Response Questions KEY page 1 1980 a) points 1s s p 6 3s 3p 6 4s 3d 10 4p 3 b) points for the two electrons in the 4s: 4, 0, 0, +1/ and 4, 0, 0, - 1/ for the three
PHOTOELECTRIC EFFECT AND DUAL NATURE OF MATTER AND RADIATIONS 1. Photons 2. Photoelectric Effect 3. Experimental Set-up to study Photoelectric Effect 4. Effect of Intensity, Frequency, Potential on P.E.
Section 7: In this section, we present a basic description of atomic nuclei, the stored energy contained within them, their occurrence and stability Basic Nuclear Concepts EARLY DISCOVERIES [see also Section
PAM1014 Introduction to Radiation Physics Basic Atomic Theory Objectives Introduce and Molecules The periodic Table Electronic Energy Levels Atomic excitation & de-excitation Ionisation Molecules Constituents
Unit 1: Atoms Level 3 Achievement Scale Can state the key results of the experiments associated with Dalton, Rutherford, Thomson, Chadwick, and Bohr and what this lead each to conclude. Can explain that
Name: Period: Due Date: Lab Partners: CHARGED PARTICLES & MAGNETIC FIELDS - WebAssign Purpose: Use the CP program from Vernier to simulate the motion of charged particles in Magnetic and Electric Fields
Quantum Mechanics and Atomic Structure 1 INTRODUCTION The word atom is derived from the Greek word, atomos, which means uncut or indivisible. It was Dalton (1808) who established that elementary constituents
u Chapter 15 Infrared Spectroscopy: Theory An important tool of the organic chemist is Infrared Spectroscopy, or IR. IR spectra are acquired on a special instrument, called an IR spectrometer. IR is used
DSH 2004 THE CURRENT-VOLTAGE CHARACTERISTICS OF AN LED AND A MEASUREMENT OF PLANCK S CONSTANT Physics 258/259 I. INTRODUCTION Max Planck (1858-1947) was an early pioneer in the field of quantum physics.
Electrons in Atoms & Periodic Table Name Warm-Ups (Show your work for credit) Date 1. Date 2. Date 3. Date 4. Date 5. Date 6. Date 7. Date 8. Electrons in Atoms & Periodic Table 2 Study Guide: Things You
SPECIMEN MATERIAL A-level PHYSICS (7408/1) Paper 1 Specimen 2014 Morning Time allowed: 2 hours Materials For this paper you must have: a pencil a ruler a calculator a data and formulae booklet. Instructions
Outline MAE 493R/593V- Renewable Energy Devices Solar Energy Electromagnetic wave Solar spectrum Solar global radiation Solar thermal energy Solar thermal collectors Solar thermal power plants Photovoltaics
DO PHYSICS ONLINE FROM QUANTA TO QUARKS QUANTUM (WAVE) MECHANICS Quantum Mechanics or wave mechanics is the best mathematical theory used today to describe and predict the behaviour of particles and waves.
2.1 Composition of the Atom Atomic Calculations number of protons + number of neutrons = mass number number of neutrons = mass number - number of protons number of protons = number of electrons IF positive
PRACTICE EXAM IV P202 SPRING 2004 1. In two separate double slit experiments, an interference pattern is observed on a screen. In the first experiment, violet light (λ = 754 nm) is used and a second-order
P19: INTRODUCTORY PHYSICS III Experiment IV: Atomic Spectra and the Bohr model Department of Physics and Astronomy Dartmouth College 6127 Wilder Laboratory Hanover, NH 03755 USA Overview In this lab, we
Spectrophotometry and the Beer-Lambert Law: An Important Analytical Technique in Chemistry Jon H. Hardesty, PhD and Bassam Attili, PhD Collin College Department of Chemistry Introduction: In the last lab
Electromagnetic Spectrum: Refer to Figure 12.1 Molecular Spectroscopy: Absorption of electromagnetic radiation: The absorptions and emissions of electromagnetic radiation are related molecular-level phenomena
Main properties of atoms and nucleus. Atom Structure.... Structure of Nuclei... 3. Definition of Isotopes... 4. Energy Characteristics of Nuclei... 5. Laws of Radioactive Nuclei Transformation... 3. Atom
Astronomy 110 Homework #04 Assigned: 02/06/2007 Due: 02/13/2007 Name: Directions: Listed below are twenty (20) multiple-choice questions based on the material covered by the lectures this past week. Choose
Blackbody radiation derivation of Planck s radiation low 1 Classical theories of Lorentz and Debye: Lorentz (oscillator model): Electrons and ions of matter were treated as a simple harmonic oscillators
Vocabulary: Define the following terms. Law of Universal Gravitation Gravity Study Guide Weight Weightlessness Gravitational Field Black hole Escape velocity Math: Be able to use the equation for the law
Chemistry 2 Chapter 13: Electrons in Atoms Please do not write on the test Use an answer sheet! 1 point/problem 45 points total 1. Calculate the energy in joules of a photon of red light that has a frequency
Chapter 2 Quantum Theory 2.0 Introduction 2.6 Orbital Shapes, Signs, and Sizes 2.1 The Nature of Light 2.7 Electron Configurations 2.2 Quantization 2.8 Quantum Theory and the Periodic Table 2.3 Bohr Model
2B30: PRACTICAL ASTROPHYSICS FORMAL REPORT: O6: The Diffraction Grating Spectrometer Adam Hill Lab partner: G. Evans Tutor: Dr. Peter Storey 1 Abstract The calibration of a diffraction grating spectrometer
Basics of Nuclear Physics and Fission A basic background in nuclear physics for those who want to start at the beginning. Some of the terms used in this factsheet can be found in IEER s on-line glossary.
Quantum Phenomena and the Theory of The Mechanics of the Very Small Waseda University, SILS, Introduction to History and Philosophy of Science . Two Dark Clouds In 1900 at a Friday Evening lecture at the
OpenStax-CNX module: m42356 1 Resistors in Series and Parallel OpenStax College This work is produced by OpenStax-CNX and licensed under the Creative Commons Attribution License 3.0 Abstract Draw a circuit
OpenStax-CNX module: m42217 1 Kinetic Theory: Atomic and Molecular Explanation of Pressure and Temperature OpenStax College This work is produced by OpenStax-CNX and licensed under the Creative Commons
Assignment 06 A 1- What is the energy in joules of an electron undergoing a transition from n = 3 to n = 5 in a Bohr hydrogen atom? a) -3.48 x 10-17 J b) 2.18 x 10-19 J c) 1.55 x 10-19 J d) -2.56 x 10-19
Determination of Molecular Structure by MOLEULAR SPETROSOPY hemistry 3 B.Z. Shakhashiri Fall 29 Much of what we know about molecular structure has been learned by observing and analyzing how electromagnetic
PHYSICS PAPER 1 (THEORY) (Three hours) (Candidates are allowed additional 15 minutes for only reading the paper. They must NOT start writing during this time.) ---------------------------------------------------------------------------------------------------------------------
As you know, some substances are made up of only one kind of atom and these substances are called elements. You already know something about a number of elements you ve heard of hydrogen, helium, silver,
Orbits of the Lennard-Jones Potential Prashanth S. Venkataram July 28, 2012 1 Introduction The Lennard-Jones potential describes weak interactions between neutral atoms and molecules. Unlike the potentials
OpenStax-CNX module: m32633 1 Quadratic Sequences Rory Adams Free High School Science Texts Project Sarah Blyth Heather Williams This work is produced by OpenStax-CNX and licensed under the Creative Commons
INFRARED SPECTROSCOPY (IR) Theory and Interpretation of IR spectra ASSIGNED READINGS Introduction to technique 25 (p. 833-834 in lab textbook) Uses of the Infrared Spectrum (p. 847-853) Look over pages
13 C NMR Spectroscopy Introduction Nuclear magnetic resonance spectroscopy (NMR) is the most powerful tool available for structural determination. A nucleus with an odd number of protons, an odd number
Chapter 3 Bohr model of hydrogen Figure 3.1: Democritus The atomic theory of matter has a long history, in some ways all the way back to the ancient Greeks (Democritus - ca. 400 BCE - suggested that all
Proton Nuclear Magnetic Resonance Spectroscopy Introduction: The NMR Spectrum serves as a great resource in determining the structure of an organic compound by revealing the hydrogen and carbon skeleton.
Friday 18 January 2013 Morning AS GCE PHYSICS B (ADVANCING PHYSICS) G492/01 Understanding Processes / Experimentation and Data Handling *G411640113* Candidates answer on the Question Paper. OCR supplied
Chapte 5 Example The helium atom has 2 electonic enegy levels: E 3p = 23.1 ev and E 2s = 20.6 ev whee the gound state is E = 0. If an electon makes a tansition fom 3p to 2s, what is the wavelength of the
Nuclear Physics Nuclear Physics comprises the study of: The general properties of nuclei The particles contained in the nucleus The interaction between these particles Radioactivity and nuclear reactions
Electrons In Atoms Mr. O Brien (SFHS) Chapter 5 Standard 1D Electrons in Atoms (std.1d) What are Bohr Models? planetary model in which the negatively-charged electrons orbit a small, positively-charged
The Advanced Placement Examination in Chemistry Part I Multiple Choice Questions Part II Free Response Questions Selected Questions from1970 to 2010 Atomic Theory and Periodicity Part I 1984 1. Which of
2. Molecular stucture/basic spectroscopy The electromagnetic spectrum Spectral region for atomic and molecular spectroscopy E. Hecht (2nd Ed.) Optics, Addison-Wesley Publishing Company,1987 Spectral regions
MASS DEFECT AND BINDING ENERGY The separate laws of Conservation of Mass and Conservation of Energy are not applied strictly on the nuclear level. It is possible to convert between mass and energy. Instead
Chapter 5 Matter Waves. Home Work s 5.1 Problem 5.10 (In the text book) An electron has a de Broglie wavelength equal to the diameter of the hydrogen atom. What is the kinetic energy of the electron? How
Chapter 5. Gravitation Notes: Most of the material in this chapter is taken from Young and Freedman, Chap. 13. 5.1 Newton s Law of Gravitation We have already studied the effects of gravity through the
Principles of Imaging Science I (RAD119) Electromagnetic Radiation Energy Definition of energy Ability to do work Physicist s definition of work Work = force x distance Force acting upon object over distance
Lesson Topics Covered SCH 3UI Unit 2 Outline Up to Quiz #1 Atomic Theory and the Periodic Table 1 Note: History of Atomic Theory progression of understanding of composition of matter; ancient Greeks and
Forensic Spectral Anaylysis: Warm up! The study of triangles has been done since ancient times. Many of the early discoveries about triangles are still used today. We will only be concerned with the "right
.1.1 Measure the motion of objects to understand.1.1 Develop graphical, the relationships among distance, velocity and mathematical, and pictorial acceleration. Develop deeper understanding through representations
Bohr Model Calculations for Atoms and Ions Frank Riou Department of Chemistry College of St. nedict St. Johnʹs University St. Joseph, MN 56374 Abstract A debroglie Bohr model is described that can be used
P.S./PHYSICS The University of the State of New York REGENTS HIGH SCHOOL EXAMINATION PHYSICAL SETTING PHYSICS Friday, June 20, 2014 1:15 to 4:15 p.m., only The possession or use of any communications device
The Models of the Atom All life, whether in the form of trees, whales, mushrooms, bacteria or amoebas, consists of cells. Similarly, all matter, whether in the form of aspirin, gold, vitamins, air or minerals,
Chapter 13 Spectroscopy NMR, IR, MS, UV-Vis Main points of the chapter 1. Hydrogen Nuclear Magnetic Resonance a. Splitting or coupling (what s next to what) b. Chemical shifts (what type is it) c. Integration
Monday 11 June 2012 Afternoon A2 GCE PHYSICS B (ADVANCING PHYSICS) G495 Field and Particle Pictures *G412090612* Candidates answer on the Question Paper. OCR supplied materials: Data, Formulae and Relationships
Lecture 3: Optical Properties of Bulk and Nano 5 nm The Previous Lecture Origin frequency dependence of χ in real materials Lorentz model (harmonic oscillator model) 0 e - n( ) n' n '' n ' = 1 + Nucleus
5.1 Evolution of the Atomic Model Studying the atom has been a fascination of scientists for hundreds of years. Even Greek philosophers, over 2500 years ago, discussed the idea of there being a smallest
Sample Exercise 6.1 Concepts of Wavelength and Frequency Two electromagnetic waves are represented in the margin. (a) Which wave has the higher frequency? (b) If one wave represents visible light and the
Chapter 28: MAGNETIC FIELDS 1 Units of a magnetic field might be: A C m/s B C s/m C C/kg D kg/c s E N/C m 2 In the formula F = q v B: A F must be perpendicular to v but not necessarily to B B F must be
activity 4 Atomic Structure OBJECTIVES Students are introduced to the structure of the atom and the nature of subatomic particles. The students are introduced to the properties of protons, neutrons, and
Curriculum for Excellence Higher Physics Success Guide Electricity Our Dynamic Universe Particles and Waves Electricity Key Area Monitoring and Measuring A.C. Monitoring alternating current signals with
PHYSICS FOUNDATIONS SOCIETY THE DYNAMIC UNIVERSE TOWARD A UNIFIED PICTURE OF PHYSICAL REALITY TUOMO SUNTOLA Published by PHYSICS FOUNDATIONS SOCIETY Espoo, Finland www.physicsfoundations.org Printed by