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Molecular Geometry and Bonding Theories

Molecular Geometry and Bonding Theories. The properties of a molecule depend on its shape and and the nature of its bonds. In this unit, we will discuss three models. . (1) a model for the geometry of molecules . -- valence-shell electron-pair repulsion (VSEPR) theory .

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Molecular Geometry and Bonding Theories

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  1. Molecular Geometry and Bonding Theories

  2. The properties of a molecule depend on its shape and and the nature of its bonds. In this unit, we will discuss three models. (1) a model for the geometry of molecules -- valence-shell electron-pair repulsion (VSEPR) theory (2) a model about WHY molecules form bonds and WHY they have the shape they do -- valence-bond theory (3) a model of chemical bonding that deals with the electronic structure of molecules -- molecular orbital (MO) theory

  3. bond angles: the angles made by the lines joining the nuclei of a molecule’s atoms carbon dioxide methane formaldehyde CO2 CH4 CH2O 180o 109.5o 120o

  4. H .. .. H– N –H N H H H VSEPR electron domain: a region in which at least two electrons are found -- they repel each other because… they are all (–) bonding domain: 2-to-6 e– that are shared by two atoms; they form a… covalent bond nonbonding domain: 2 e– that are located on a single atom; also called a… lone pair For ammonia, there are three bonding domains and one nonbonding domain. NH3 4 e– domains Domains arrange themselves so as to minimize their repulsions.

  5. .. .. N H H H The electron-domain geometry is one of five basic arrangements of domains. -- it depends only on the total # of e– domains, NOT the kind of each domain The molecular geometry describes the orientation of the atoms in space. -- it depends on how many of each kind of e– domain

  6. linear linear (CO2) trigonal planar trigonal planar (BF3), bent (NO2) tetrahedral tetrahedral (CH4), trigonal pyramidal (NH3), bent (H2O) “atoms – axial” trig. bipyramidal (PCl5), linear (XeF2) seesaw (SF4), T-shaped (ClF3) trigonal bipyramidal octahedral octahedral (SF6), sq. pyr. (BrF5), square planar (XeF4)

  7. Cl .. [ ] .. .. – .. .. .. .. .. .. .. Cl– Sn –Cl .. .. O .. .. .. –O .. Cl–Se–Cl .. .. .. .. O= .. .. .. .. .. .. .. O– .. O O= .. .. To find the electron-domain geometry (EDG) and/or molecular geometry (MG), draw the Lewis structure. Multiple bonds count as a single domain. Predict the EDG and MG of each of the following. SnCl3– EDG: tetrahedral MG: trig. pyramidal 26 e– O3 EDG: trig. planar MG: bent 18 e– SeCl2 EDG: tetrahedral MG: bent 20 e–

  8. [ ] .. .. 2– .. C= .. O– O .. .. .. .. O F F F .. .. .. .. F .. .. –F .. .. I –F F– .. .. .. .. .. .. .. .. F .. .. .. .. .. .. .. .. .. .. .. F– .. –F .. S F– –F .. .. Cl .. .. .. .. .. .. CO32– EDG: trig. planar (res.) MG: trig. planar 24 e– SF4 EDG: trig. bipyr. .. MG: seesaw 34 e– IF5 EDG: octahedral .. MG: sq. pyramidal 42 e– ClF3 EDG: trig. bipyr. .. MG: T-shaped 28 e–

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