CH110-120 Chapter 5 Lecture Notes Powerpoint

CH110-120 Chapter 5 Lecture Notes Powerpoint - Chapter 5...

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Chapter 5 – Atomic Energies and Periodicity 5.1 Orbital Energies 5.2 Structure of the Periodic Table 5.3 Electron Configurations 5.4 Periodicity of Atomic Properties 5.5 Energetics of Ionic Compounds 5.6 Ions and Chemical Periodicity
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Review: Atomic Orbitals Atomic orbitals are represented by 4 quantum numbers (n, l, m l and m s ) Orbitals have different energies Orbitals have shapes that describe the probable location of an electron
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5.1 Orbital Energies In the last chapter, we discussed atoms and energy levels. When an atom absorbed energy, an electron within the atom was promoted to a higher energy level. We also learned about the atomic orbitals which are represented by n, l, m l and m s
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Clicker Question: Which of the following set of quantum numbers is not possible? a. n =2, l = 1, m l = 0, m s =1/2 b. n =3, l = 2, m l = 2, m s =1/2 c. n =4, l = 2, m l = 2, m s = -1/2 d. n =3, l = 3, m l = 2, m s = -1/2 e. n = 2, l = 1, m l = 1, m s = -1/2
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Orbital Energy When a hydrogen atom absorbs light, the energy of the photon converts it from the ground state to an excited state . In the process, its electron transfers to an orbital that is larger and less stable. How do we measure the stability of an orbital?
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Ionization Energy Ionization Energy – energy required to remove one electron from an atom H H + + e - IE H = 2.18 x 10 -18 J He + He 2+ (g) + e - IE He+ = 8.72 x 10 -18 J Note that H and He + both have only one electron The IE for He + is 4X greater than for H….WHY?
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Effect of Nuclear Charge Let’s look at the atomic emission spectra and the energy level diagrams of H and He + :
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Screening As a free electron approaches a positive cation, it will be attracted to the nucleus. But, it is also repelled by any electrons orbiting the nucleus. The electron-electron repulsion is canceled by the attraction to the nucleus. This is referred to as screening. The higher the value of the l quantum number, the more that orbital is screened by electrons in smaller, more stable orbitals.
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Screening Electrons are only screened by inner electrons. An electron in the 2s orbital is screened only by the 1s. An electron in the 3s orbital is screened by the 1s and 2s.
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Example 5 - 1 Make an electron density plot showing the 1s, 2p and 3d orbitals to scale. Label the plot in a way that summarizes the screening properties of these orbitals. Suggested Problems: End of Chapter Exercises: 5.1, 5.3, 5.5
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It is more difficult to remove an electron from a positive species. The total number of electrons in an atom affects the ionization energy. A negatively charged electron in a multielectron atom is attracted to the positively charged nucleus, but repelled by the other negatively charged electrons. Energy level of orbital where the electron is found
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This note was uploaded on 10/14/2011 for the course CHEM 110 taught by Professor Maly during the Fall '10 term at Wilfred Laurier University .

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CH110-120 Chapter 5 Lecture Notes Powerpoint - Chapter 5...

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