CHM1045 Exam #3 Study GuideChapter 7: Quantum Theory and the Electronic Structure of AtomsA Theory that Explains Electron Behavior- Electron behavior determines much of the behavior of atomsoNumber of valence electronsValence Electrons: Outermost shell electronsoNothing to do with the nucleus- Quantum-Mechanical Model: Explains the manner electrons exist and behave inatoms- Helps us understand & predict the properties of atoms that are directly related to the behavior of the electronsoWhy some elements are metals while others are nonmetalsoWhy some elements gain 1 electron when forming an anion, while others gain 2oWhy some elements are very reactive while others are practically inertoOther periodic patterns we see in the properties of the elementsThe Nature of Light: Wave Nature- Light is a form of electromagnetic radiationoComposed of perpendicular oscillating wavesOne 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 waveoMeasures how intense the light isoThe larger the amplitude, the brighter the light1CHM1045 Exam #3 Study Guide- Wavelength (): A measure of the distance covered by the waveoUnits 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 oUnits: hertz (Hz) or cycles/s = s-1ocycles / second 1 / second sec-1- The total energy is proportional to the amplitude and frequency of the wavesoThe larger the amplitude, the more force it hasoThe more frequently the waves strike, the more total force there isThe 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 proportionaloSince the speed of light is constant, if we know wavelength, we can find the frequency, and vice versa = c / = c / = hc / E2CHM1045 Exam #3 Study Guide mcssm1-- Practice Problem #7.1oCalculate the wavelength of a radio signal with a frequency of 100.7 mHz2.98 mColor- The color of light is determined by its wavelength (or frequency)- White light is a mixture of all the colors of visible lightoRedOrangeYellowGreenBlueViolet- The observed color of objects is predominantly the colors of white light that are reflectedThe 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 energyoRadiowave light has the lowest energyoGamma ray light has the highest energy3CHM1045 Exam #3 Study GuideThe Nature of Light: Particle Nature- Einstein proposed that light energy was delivered to atoms in packets called quanta or photonso“Particles” of lighto“Tiny packets of energy”oPhotons don’t have a mass (so not an actual particle)oOnly considered particles because they are the smallest indivisible part of light- The energy of a photon of light was directly proportional to its frequencyoInversely proportional to its wavelengthoPlanck’s Constant (h): Proportionality constant6.626 x 10-34 J-sE = hE = h-c / chhE-- Practice Problem #7.2oWhat 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 Hz16.67 m- Energy of the beam is not equal to the energy of the photons in itNature of Electrons: Wave Nature- de Broglie proposed that particles could have wave-like character4CHM1045 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 its momentum = h / m-u )s(m(kg)smkgm1-22velocitymassh---- Practice Problem #7.3oDetermine the wavelength of a neutron traveling at 1.00 x 102 m/soMassneutron = 1.675 x 10-24 kg3.96 nmBohr’s Model- Bohr proposed that the electrons could only have very specific amounts of energyoFixed amounts = quantized- The electrons traveled in orbits that were a fixed distance from the nucleus (stationary states)oTherefore, the energy of the electron was proportional to the distance the orbital was from the nucleus- Electrons emitted radiation when they “jumped” from an orbit with higher energy down to an orbit with lower energyoThe distance between the orbits determined the energy of the photon of light produced5CHM1045 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) oEmission- Ex) Electron falls from n = 3 to n = 2, electron emits red lightComplimentary Properties- 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 oAs you know more about one, you know less about the otheroHeisenberg’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 electronsSchrodinger Wave Function/Equation: Describing the Electron6CHM1045 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 Numberson: Principal quantum numberol: Angular momentum quantum numberom1: Magnetic quantum numberoms: Spin quantum numberPrincipal Quantum Number n - Characterizes the energy of the
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