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LectureNote2 - Electronic structures of many-electron atoms...

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1 Electronic structures of many-electron atoms For a hydrogen-like atom Atomic orbitals E ? Atomic orbitals ? For a many-electron atom One-electron atoms Considering electron-electron repulsion
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2 Difference between one-electron (hydrogen-like) atoms and many-electron atoms E(2s) < E(2p) why ? Shielding ( 屏蔽 ) effects in many-electron systems Effective Nuclear Charge (Z eff ): the nuclear charge experienced the nuclear charge experienced by the outermost electrons by the outermost electrons Outer electrons are shielded from nuclear charge by inner electrons reduce electro- static attraction between positively-charged protons in nucleus and the outer electrons 3p Li 4p Be 5p B
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3 Electron configurations How are the electrons distributed in the various atomic orbitals? The set of four quantum numbers can be regarded as the "address" of an electron in an atom. Representations Letter representation: Box representation: H: 1s 1 He: 1s 2 B: 1s 2 2s 2 2p 1 H: He: B: 1s 2s 2p
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4 Three rules we have to follow when we write an electron configuration The aufbau principle: The electron configurations are built up from the bottom, using the lowest energy orbitals first. Hund's rule: The most stable arrangement of electrons in subshells is the the one with the greatest number of parallel spins. N: 1s 2s 2p The Pauli exclusion principle: No two electrons in an atom can have the same four quantum numbers. In other words, only two electrons may occupy the same atomic orbital having opposite spins.
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5 Abbreviated Electron Configurations
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6 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p
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7 Valence electrons + core electrons
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8 Periodic table and periodicity Electron configurations
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9 Valence electrons the outer electrons of an atom, which are those involved in chemical bonding, are often called the valence electrons. Elements in the same group of the periodic table have analogous valence-electron configurations.
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13 Periodic table and periodicity Exceptions Examples: Group 6 and Group 10 elements Valence electrons + Core electrons Periodic variation in physical properties Effective Nuclear Charge (Z eff ) Outer electrons are shielded from nuclear charge by inner electrons reduce electrostatic attraction between positively-charged protons in nucleus and the outer electrons
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14 Atomic Radius Measure distance between centers of bonded atoms decreases from left to right across a period; increases going down a column Ionic Radius (the size of a cation or an anion)
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LectureNote2 - Electronic structures of many-electron atoms...

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