Chapter07-PREVIEW-SPRING2008

Chapter07-PREVIEW-SPRING2008 - Development of the Periodic...

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Development of the Periodic Table Elements in the same group generally have similar chemical properties. Properties are not identical , however.
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Brief History of the Periodic Table 1829: Johann Dobereiner found several groups of 3 elements (Dobereiner’s Triads) that had similar properties. Examples include (Ca, Sr, Ba) and (Cl, Br, I). 1864: John Newlands suggested that elements should be arranged in “octaves” (groups of eight). 1872: Dmitri Mendeleev and Julius Lothar Meyer Independently developed the Periodic Table, in which elements were ordered by increasing atomic mass . 1913: Henry Moseley realized that elements should be arranged by atomic number ( Z = number of protons in nucleus), rather than atomic mass.
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Brief History of the Periodic Table By arranging elements by atomic number (instead of atomic weight) we can account for some anomalies and put similar elements in the same group. Examples of Anomalies Element Atomic Mass Atomic Number Co 58.933200 27 Ni 58.6934 28 Te 127.60 52 I 126.90447 53
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Development of the Periodic Table Dmitri Mendeleev and Lothar Meyer independently came to the same conclusion about how elements should be arranged in groups.
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Development of the Periodic Table Mendeleev predicted the discovery of germanium (which he called eka -silicon) as an element with an atomic weight between that of zinc and arsenic, but with chemical properties similar to those of silicon.
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Periodic Trends We will rationalize observed trends in Sizes of atoms and ions. Ionization energy. Electron affinity.
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The Aufbau Principle Revisited We use the Aufbau Principle to construct the electron configuration. This is a theoretical construct in which an atomic with a nuclear charge (atomic number) of Z+1 is derived from an atom of nuclear charge Z by simultaneously adding one proton to the nucleus and one electron to the electron configuration . The order in which we add electrons does not necessarily reflect the relative energies of the orbitals in the final electron configuration. The ion M + is derived by removing an electron from the orbital with the highest principle quantum number ( n ) even if the last electron
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ns 1 2 np 3 4 5 6 d 10 4f 5f Ground State Electron Configurations of the Elements
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The Aufbau Principle Revisited Consider the following electron configurations: Even though we added the last electron for Mn and Zn to the 3d orbital, we take out two 4s electrons to produce Mn 2+ ( [Ar]3d 5 ) and Zn 2+ ( [Ar]3d 10 )
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In a many-electron atom, an electron is attracted by the nucleus , but is also repelled by other electrons . The nuclear charge
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This note was uploaded on 04/29/2008 for the course CHE 101 taught by Professor Churchhill during the Spring '08 term at SUNY Buffalo.

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Chapter07-PREVIEW-SPRING2008 - Development of the Periodic...

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