Chapter8 - 1 Chapter Eight Electron Configurations, Atomic...

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1 Chapter Eight Chapter Eight Electron Configurations, Atomic Properties, and the Periodic Table
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2 Orbital Energy Diagrams Subshells within a shell are at the same energy level in hydrogen: 2 s = 2 p. Subshells are split in a multielectron atom: 2 s < 2 p. Orbital energies are lower in a multielectron atom … …than in the hydrogen atom.
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3 An electron configuration describes the distribution of electrons among the various orbitals in the atom. Electron configuration is represented in two ways. Electron Configurations The spdf notation uses numbers to designate a principal shell and letters ( s, p, d, f ) to identify a subshell; a superscript indicates the number of electrons in a designated subshell.
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4 In an orbital (box) diagram a box represents each orbital within subshells, and arrows represent electrons. The arrows’ directions represent electron spins; opposing spins are paired. Electron Configurations N:
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5 1. Electrons ordinarily occupy orbitals of the lowest energy available. 2. Pauli exclusion principle : one atomic orbital can accommodate only two electrons, and these electrons must have opposing spins. Therefore, no two electrons in the same atom may have all four quantum numbers alike. 3. Hund’s rule : Electrons in the same subshell occupy the orbitals singly, with spins parallel, before they are paired Rules for Electron Configurations
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6 Order of Subshell Energies Follow the arrows from the top: 1 s , 2 s , 2 p , 3 s , 3 p , 4 s , 3 d , 4 p , etc. Subshells that are far from the nucleus may exhibit exceptions to the filling order.
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7 The Aufbau principle describes a hypothetical “building- up” of an atom from the one that precedes it in atomic number. ( Z = 1) H 1 s 1 ( Z = 2) He 1 s 2 ( Z = 3) Li 1 s 2 2 s 1 Noble-gas-core abbreviation : we can replace the portion that corresponds to the electron configuration of a noble gas with a bracketed chemical symbol. It’s easier to write … ( Z = 3) Li [He] 2 s 1 ( Z = 22) Ti [Ar] 4 s 2 3 d 2 The Aufbau Principle To get He, add one electron to H. To get Li, add one electron to He.
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8 The main group elements are those in which the orbital being filled in the aufbau process is an s or a p orbital of the outermost shell . Main Group and Transition Elements In transition elements , the subshell being filled in the aufbau process is in an inner principal shell.
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9 Using the Periodic Table to Write Electron Configurations The electron configuration of Si ends with 3 s 2 3 p 2 The electron configuration of Rh ends with 5 s 2 4 d 7
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10 Example 8.2 Give the complete ground-state electron configuration of a strontium atom (a) in the spd f notation and (b) in the noble- gas-core abbreviated notation.
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11 Exceptions to the Aufbau Principle Half-filled d subshell plus half-filled s subshell has slightly lower in energy than s 2 d 4 . Filled
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Chapter8 - 1 Chapter Eight Electron Configurations, Atomic...

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