Chapter 2 - Electron - Wave or particle? Electron beam...

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Electron - Wave or particle? Electron beam exerts a measurable pressure. Electrons have a finite mass. It is impossible to determine the exact position for an electron. A diffraction pattern is observed when a beam of electrons is passed through a narrow slit.
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Wave Properties of Electrons Standing wave vibrates in fixed location. Wave function, ψ , mathematical description of size, shape, orientation Amplitude may be positive or negative Node: amplitude is zero + _ + - =>
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Atomic and Molecular Orbitals Position of an electron at an atom is defined by an atomic orbital. Position of an electron at a molecule is defined by a molecular orbital . Atomic orbitals are used to construct molecular orbitals.
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Conservation of orbitals. Number of atomic orbitals = number of molecular orbitals Two atomic orbitals combine to form: One bonding molecular orbital that contains two electrons One anti-bonding molecular orbital that contains zero electrons Most stable molecules contain even number of electrons. Odd (radical) electrons are placed into nonbonding molecular orbitals.
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H 2 : s-s overlap =>
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Sigma Bonding Electron density lies between the nuclei. A bond may be formed by s-s , p-p , s-p , or hybridized orbital overlaps. Single region of overlap The bonding MO is lower in energy than the original atomic orbitals. The antibonding MO is higher in energy than the atomic orbitals. =>
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Cl 2 : p-p overlap => Constructive overlap along the same axis forms a sigma bond.
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Pi Bonding Pi bonds form across a framewrok of sigma bonds. Sideways overlap of parallel p orbitals. =>
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Multiple Bonds A double bond (2 pairs of shared electrons) consists of a sigma bond and a pi bond. A triple bond (3 pairs of shared electrons) consists of a sigma bond and two pi bonds. =>
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Tetrahedral Planar Linear VSEPR [valence shell electron pair repulsion] theory provides rationalization for geometry Bonding can not be obtained with s and p orbitals Molecular orbitals obtained by hybridation of s and p orbitals.
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sp Hybrid Orbitals 2 VSEPR pairs Linear electron pair geometry 180° bond angle =>
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sp 2 Hybrid Orbitals 3 VSEPR pairs Trigonal planar e - pair geometry 120° bond angle =>
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This note was uploaded on 01/12/2009 for the course CHE 201 taught by Professor Bong during the Fall '08 term at SUNY Buffalo.

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Chapter 2 - Electron - Wave or particle? Electron beam...

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