CHM1045 Exam 3 Study Guide Chapter 7 Quantum Theory and the Electronic Structure of Atoms A Theory that Explains Electron Behavior Electron behavior determines much of the behavior of atoms o Number of valence electrons Valence Electrons Outermost shell electrons o Nothing to do with the nucleus Quantum Mechanical Model Explains the manner electrons exist and behave in Helps us understand predict the properties of atoms that are directly related to atoms the behavior of the electrons o Why some elements are metals while others are nonmetals o Why some elements gain 1 electron when forming an anion while others gain 2 o Why some elements are very reactive while others are practically inert o Other periodic patterns we see in the properties of the elements The Nature of Light Wave Nature Light is a form of electromagnetic radiation o Composed of perpendicular oscillating waves One for the electric field one for the magnetic field Electric Field A region where an electrically charged particle experiences a force Magnetic Field A region where a magnetized particle experiences a force All electromagnetic waves move through space at the same constant speed Speed of Light c 3 00 x 108 m s in a vacuum Characterizing Waves Amplitude The height of the wave o Measures how intense the light is o The larger the amplitude the brighter the light 1 CHM1045 Exam 3 Study Guide Wavelength A measure of the distance covered by the wave o Units of wavelength are usually in nanometers nm Frequency The number of waves number of cycles that pass a point in a given period of time o Units hertz Hz or cycles s s 1 o cycles second 1 second sec 1 The total energy is proportional to the amplitude and frequency of the waves o The larger the amplitude the more force it has o The more frequently the waves strike the more total force there is The Relationship Between Wavelength and Frequency For waves or electromagnetic radiation traveling at the same speed the shorter the wavelength the more frequently they pass The wavelength and frequency of electromagnetic waves are inversely o Since the speed of light is constant if we know wavelength we can find the frequency and vice versa proportional c c hc E 2 CHM1045 Exam 3 Study Guide s 1 c m s m Practice Problem 7 1 2 98 m Color o Calculate the wavelength of a radio signal with a frequency of 100 7 mHz The color of light is determined by its wavelength or frequency White light is a mixture of all the colors of visible light o RedOrangeYellowGreenBlueViolet The observed color of objects is predominantly the colors of white light that are reflected The Electromagnetic Spectrum Visible light comprises only a small fraction of all the wavelengths of light Electromagnetic Spectrum All the wavelengths of light Amplitude tells you about the frequency or brightness Short wavelength high frequency light has high energy o Radiowave light has the lowest energy o Gamma ray light has the highest energy 3 CHM1045 Exam 3 Study Guide The Nature of Light Particle Nature Einstein proposed that light energy was delivered to atoms in packets called quanta or photons o o Particles of light Tiny packets of energy Photons don t have a mass so not an actual particle o o Only considered particles because they are the smallest indivisible part of light The energy of a photon of light was directly proportional to its frequency Inversely proportional to its wavelength o o Planck s Constant h Proportionality constant 6 626 x 10 34 J s E h E h c hE ch Practice Problem 7 2 o What is the frequency of radiation required to supply 1 0 x 102 J of energy from 8 5 x 1027 photons What is the wavelength of this radiation 1 8 x 107 s 1 or Hz 16 67 m Energy of the beam is not equal to the energy of the photons in it Nature of Electrons Wave Nature de Broglie proposed that particles could have wave like character 4 CHM1045 Exam 3 Study Guide Because it is so small the wave character of electrons is significant de Broglie s Formula The wavelength of a particle is inversely proportional to 2 mkg 2 s h velocity m 1 s its momentum h m u m mass kg Practice Problem 7 3 3 96 nm Bohr s Model o Determine the wavelength of a neutron traveling at 1 00 x 102 m s o Massneutron 1 675 x 10 24 kg Bohr proposed that the electrons could only have very specific amounts of energy o Fixed amounts quantized The electrons traveled in orbits that were a fixed distance from the nucleus o Therefore the energy of the electron was proportional to the distance the Electrons emitted radiation when they jumped from an orbit with higher energy stationary states orbital was from the nucleus down to an orbit with lower energy light produced o The distance between the orbits determined the energy of the photon of 5 CHM1045 Exam 3 Study Guide n 1 is the lowest energy state The higher the n the higher the energy of that state It s easier to take an electron away or ionize and electron from the n 5 orbital than the n 1 orbital Exciting an electron with some form of light makes it go up levels Energy released in the form of a photon when an electron falls o Emission Complimentary Properties Ex Electron falls from n 3 to n 2 electron emits red light When you try to observe the wave nature of the electron you cannot observe its particle nature and vice versa The wave and particle nature of the electron are complimentary properties o As you know more about one you know less about the other o Heisenberg s Uncertainty Principle The best we can do is to describe the probability an electron will be found in a particular region using statistical functions Orbitals The regions in the atom of high probability of finding electrons Schrodinger Wave Function Equation Describing the Electron 6 CHM1045 Exam 3 Study Guide Calculations show that the size shape and orientation in space of an orbital are determined by three integer terms in the wave function There is a fourth number that determines the spin of an electron The wave function is a mathematical function that explains and characterizes the position and energy of an electron in the atom Quantum Numbers o n Principal quantum number l Angular momentum quantum number o o m1 Magnetic quantum number o ms Spin quantum number n Principal Quantum Number Characterizes the energy of the electron in a particular orbital o Bohr s energy levels Can be any integer greater than 1 The larger the value of n the more energy the orbital has As n gets larger the amount of energy between orbitals gets smaller Energies are
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