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1 Ch 4 Electron Energies

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2 Electromagnetic Spectrum Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels though space. Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels though space. EM radiation is organized into a spectrum according to wavelength ( ) and frequency (v) of the waves. EM radiation is organized into a spectrum according to wavelength ( ) and frequency (v) of the waves. The spectrum includes the areas; radio waves, infrared, visible light, ultraviolet, x- rays, and gamma rays. The spectrum includes the areas; radio waves, infrared, visible light, ultraviolet, x- rays, and gamma rays.

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4 Mathematical Relationships Wavelength and frequency are inversely proportional. As one increases, the other decreases. Wavelength and frequency are inversely proportional. As one increases, the other decreases. The speed of EM waves is related to wavelength and frequency in the following way. c = v The speed of EM waves is related to wavelength and frequency in the following way. c = v Because the speed of light is constant, it is possible to conclude that wavelength and frequency are inversely proportional. Because the speed of light is constant, it is possible to conclude that wavelength and frequency are inversely proportional.

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5 Photons All areas on the electromagnetic spectrum carry particles of electromagnetic radiation called photons. All areas on the electromagnetic spectrum carry particles of electromagnetic radiation called photons. A photon has zero mass but carries a quantum of energy. A photon has zero mass but carries a quantum of energy. quantum of energy quantum of energy

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6 Quanta This minimum energy contained by the photon is called quantum energy. This minimum energy contained by the photon is called quantum energy. This quantum energy is determined by the frequency of the radiation carried by the photon. E = hv This quantum energy is determined by the frequency of the radiation carried by the photon. E = hvE = hvE = hv

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7 Planck It was Planck who discovered that all energy comes in these packets of quanta. It was Planck who discovered that all energy comes in these packets of quanta. He was able to prove photons of quantum energy existed by observing the photoelectric effect. He was able to prove photons of quantum energy existed by observing the photoelectric effect.

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8 Photoelectric Effect Photoelectric Effect When light shines on metal, photons in the light can knock electron’s off of the atoms in the metal. When light shines on metal, photons in the light can knock electron’s off of the atoms in the metal. This only occurs if the photon that hits the metal has at least the minimum energy required to knock the electron loose. This only occurs if the photon that hits the metal has at least the minimum energy required to knock the electron loose. Therefore, matter absorbs only whole numbers of photons of EM energy. Therefore, matter absorbs only whole numbers of photons of EM energy.

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10 Jumping Electrons Photons not only knock electrons lose from an atom, they can also be absorbed or released from an atom. Photons not only knock electrons lose from an atom, they can also be absorbed or released from an atom. Photons of energy can be absorbed by electrons in an atom causing the atom to be at an excited state. Photons of energy can be absorbed by electrons in an atom causing the atom to be at an excited state. Photons can also be released by electrons in an atom causing the atom to be at ground state. Photons can also be released by electrons in an atom causing the atom to be at ground state.

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11 Orbital Energy When current is passes through a gas at low pressure, the atoms within the gas become excited. When current is passes through a gas at low pressure, the atoms within the gas become excited. As an electron falls from the excited state to the ground state, energy is given off in the form of a photon of radiation. As an electron falls from the excited state to the ground state, energy is given off in the form of a photon of radiation. The energy of the photon is equal to the difference in energy between the two orbits. The energy of the photon is equal to the difference in energy between the two orbits. Ephoton = E2 - E1 Ephoton = E2 - E1

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12 Emission/absorption Spectra The released photon of radiation can be sent through a prism where it becomes separated into its specific frequencies, forming a line-emission spectrum. The released photon of radiation can be sent through a prism where it becomes separated into its specific frequencies, forming a line-emission spectrum. The color and position of the light on the emission spectrum relate to the wavelength and frequency of the photon and therefore its quantum energy. The color and position of the light on the emission spectrum relate to the wavelength and frequency of the photon and therefore its quantum energy.

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13 Continuous or Line Spectra Because they originally thought atoms would become excited by any amount of energy added, it was thought this spectrum would be continuous. Because they originally thought atoms would become excited by any amount of energy added, it was thought this spectrum would be continuous. Instead the spectrum that was produced had only lines of distinct frequencies. Instead the spectrum that was produced had only lines of distinct frequencies. This indicated that only fixed amounts of energy, quanta, were being released or absorbed as electrons moved between orbits. This indicated that only fixed amounts of energy, quanta, were being released or absorbed as electrons moved between orbits.

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15 Quantized Energy Levels This fixed line spectrum suggested that energy differences between the atom’s energy states were also fixed. This fixed line spectrum suggested that energy differences between the atom’s energy states were also fixed. These set energy levels were named orbits. These set energy levels were named orbits. The energy of the orbits increases with increasing distance from the nucleus. The energy of the orbits increases with increasing distance from the nucleus.

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16 Bohr Atomic Model Bohr Atomic Model Bohr proposed a hydrogen atom model that links the atom’s single electron with its photon line emission spectrum. Bohr proposed a hydrogen atom model that links the atom’s single electron with its photon line emission spectrum. Bohr found the wavelength from the radiation’s frequency on the line emission spectrum. Bohr found the wavelength from the radiation’s frequency on the line emission spectrum. Using the wavelength, he calculated the energies that an electron must have to have at each energy level. Using the wavelength, he calculated the energies that an electron must have to have at each energy level. This technique allowed him to model the hydrogen atom correctly, but doesn’t work very well with atoms containing more than one electron. This technique allowed him to model the hydrogen atom correctly, but doesn’t work very well with atoms containing more than one electron.

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18 Particle/Wave Duality It was already known that electrons exhibited particle like qualities. It was already known that electrons exhibited particle like qualities. However, the fact that electrons confined to orbits produce only certain frequencies, they were exhibiting wave like properties as well. However, the fact that electrons confined to orbits produce only certain frequencies, they were exhibiting wave like properties as well.

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19 De Broglie De Broglie found more evidence for the wave like properties of electrons De Broglie found more evidence for the wave like properties of electrons Electrons interact with one another just as waves do. Electrons interact with one another just as waves do. They diffract/bend as they pass by the edge of an object. They diffract/bend as they pass by the edge of an object. They can interfere with one another, producing areas of constructive and destructive interference. They can interfere with one another, producing areas of constructive and destructive interference.

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21 Quantum Theory Quantum theory mathematically describes the wave properties of very small objects such as electrons. Quantum theory mathematically describes the wave properties of very small objects such as electrons. It has become the leading branch of physics that deals with atomic and subatomic systems It has become the leading branch of physics that deals with atomic and subatomic systems

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22 Orbitals Based on Heisenberg’s principle, only the probability of the location of an electron can be determined. Based on Heisenberg’s principle, only the probability of the location of an electron can be determined. Therefore, Bohr’s theory of neat orbits was thrown out. Therefore, Bohr’s theory of neat orbits was thrown out. Instead, it is now thought that electrons orbit the nucleus in three dimensional regions called orbitals. Instead, it is now thought that electrons orbit the nucleus in three dimensional regions called orbitals. The orbital give the probable location of an electron. The orbital give the probable location of an electron.

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23 Heisenberg Uncertainty Principle Electrons are detected by their interaction with photons. But any attempt to locate an electron with a photon knocks the electron off its course. Electrons are detected by their interaction with photons. But any attempt to locate an electron with a photon knocks the electron off its course. As a result there is a basic uncertainty in trying to locate an electron. As a result there is a basic uncertainty in trying to locate an electron. Heisenberg’s principle states that it is impossible to determine the position and speed of an electron at the same time. Heisenberg’s principle states that it is impossible to determine the position and speed of an electron at the same time. Although difficult for scientists to accept, it has become one of the fundamental principles of our present understanding of light and matter. Although difficult for scientists to accept, it has become one of the fundamental principles of our present understanding of light and matter.

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25 Quantum Numbers Quantum numbers describe the properties of orbits and the electrons within the orbits. Quantum numbers describe the properties of orbits and the electrons within the orbits. Quantum numbers Quantum numbers Using these, it is possible to figure out why each orbit contains its specified amount of electrons. Using these, it is possible to figure out why each orbit contains its specified amount of electrons.

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26 Principle Quantum Number The principle quantum number, n, gives the main energy level occupied by the electron. The principle quantum number, n, gives the main energy level occupied by the electron. Electrons that share the same main energy level are said to be in the same shell. Electrons that share the same main energy level are said to be in the same shell. n=11 st shell n=11 st shell n=22 nd shell n=33 rd shell

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27 Angular Momentum Quantum Number Angular momentum quantum number, L, indicates the sublevels in the main shell. Angular momentum quantum number, L, indicates the sublevels in the main shell. L values are zero and all numbers less than n. L values are zero and all numbers less than n. The L values correspond to certain shapes of orbits. The L values correspond to certain shapes of orbits. 0 = s-shaped and spherical 0 = s-shaped and sphericals-shaped 1 = p-shaped and dumbbell shaped 2 = d-shaped and cross shaped

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28 Magnetic Quantum Number Magnetic quantum number, m, gives the orientation of an orbital around a nucleus. Magnetic quantum number, m, gives the orientation of an orbital around a nucleus. s = 1 orientation s = 1 orientation p = 3 orientations d = 5 orientations The total number of orbitals within each shell is n 2. The total number of orbitals within each shell is n 2. Each orientation of an orbital can hold two electrons. Each orientation of an orbital can hold two electrons. Therefore the total number of electrons per shell is 2n 2. Therefore the total number of electrons per shell is 2n 2.

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30 Spin Quantum Number Spin quantum number indicates the spin of the electrons in each orbit Spin quantum number indicates the spin of the electrons in each orbit The spin of electrons in the same orbit must be opposites. The spin of electrons in the same orbit must be opposites. The two values of these spins are + ½ and – ½. The two values of these spins are + ½ and – ½.

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31 Electron Configuration Notation Gives the main energy levels and sublevels of the element. Gives the main energy levels and sublevels of the element. The number of electrons in each sublevel is also shown in superscript. The number of electrons in each sublevel is also shown in superscript. You start at 1s and continue filling up until the correct number of electrons are used. You start at 1s and continue filling up until the correct number of electrons are used. 1s 2 2s 2 2p 6 …… 1s 2 2s 2 2p 6 …… 1s 2 2s 2 2p 6 1s 2 2s 2 2p 6

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32 Noble Gas Notation This shortened version of electron configuration allows noble gas symbols to represent part of the configuration. This shortened version of electron configuration allows noble gas symbols to represent part of the configuration. The noble gas that occurs before the element on the periodic table is the one used. The noble gas that occurs before the element on the periodic table is the one used. Only the notation after that noble gas has to be written. Only the notation after that noble gas has to be written.notation

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33 Orbital Notation In this notation, an orbital is represented by a line with the main level and sublevel written underneath it. In this notation, an orbital is represented by a line with the main level and sublevel written underneath it.orbital Arrows showing electrons and their spin is written above the line. Each line can only hold two electrons. Arrows showing electrons and their spin is written above the line. Each line can only hold two electrons. It is necessary to write the notation for the level as may times as there is orientations for that level. It is necessary to write the notation for the level as may times as there is orientations for that level.

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34 Three Principles There are three principles that must be followed when writing electron configurations and orbital notations. There are three principles that must be followed when writing electron configurations and orbital notations. Aufbau principle- an electrons occupies the lowest-energy orbital it can. Aufbau principle- an electrons occupies the lowest-energy orbital it can. Pauli exclusion principle- no two electrons in the same orbit can have the same spin quantum number. Pauli exclusion principle- no two electrons in the same orbit can have the same spin quantum number. Hund’s rule- orbitals of equal energy must each have one electron before any is allowed to have a second. Hund’s rule- orbitals of equal energy must each have one electron before any is allowed to have a second.

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