VSEPR theory, determination

Based on the VSEPR theory, determine the structure and the symmetry point group of the following species. 

For each compound, draw the Lewis structure, determine the geometry using VSEPR theory, determine whether the molecule is polar, identify the hybridization of all interior atoms, and make a sketch of the molecule, according to valence bond theory, showing orbital overlap. 

The shapes of covalent compounds are determined by the tendency for bonding pairs to be as far apart as possible whilst lone pairs have a greater effect than bonding pairs (VSEPR theory). 

STRATEGY The existence of residual entropy at T = 0 suggests that the molecules are disordered. From the shape of the molecule (which can be obtained by using VSEPR theory), we need to determine how many orientations, W, it is likely to be able to adopt in a crystal then we can use the Boltzmann formula to see whether that number of orientations leads to the observed value of S. 

In using the VSEPR theory to determine the molecular geometry, start first with the electron group geometry, make the nonbonding electrons mentally invisible and then describe what remains. 

The VSEPR theory is only one way in which the molecular geometry of molecules may be determined. Another way involves the valence bond theory. The valence bond theory describes covalent bonding as the mixing of atomic orbitals to form a new kind of orbital, a hybrid orbital. Hybrid orbitals are atomic orbitals formed as a result of mixing the atomic orbitals of the atoms involved in the covalent bond. The number of hybrid orbitals formed is the same as the number of atomic orbitals mixed, and the type of hybrid orbital formed depends on the types of atomic orbital mixed. Figure 11.7 shows the hybrid orbitals resulting from the mixing of s, p, and d orbitals. 

Determine the shape of SiFe " using VSEPR theory. 

Use VSEPR theory to predict the shape of each of the following molecules. From the molecular shape and the polarity of the bonds, determine whether or not the molecule is polar. 

Q iai f For the compound, GeH4, use VSEPR theory to determine its molecular shape and indicate whether or not this molecule is polar. 

Use VSEPR theory to determine the shape of each molecule. 

The compounds with three ligands should have the T-shaped stereochemistry characteristic of 10-electron species on VSEPR theory. For three carbon ligands, triphenyliodine, prepared from diphenyliodine(III) iodide and phenyllithium at -80 °C in ether,61 decomposes at —10 °C, and even more stable compounds, with cyclic structures involving the iodine atom,62 still decompose over relatively short periods. No crystal structures have been determined, although NMR studies support the structural assignment.62... 

Place the atoms in the correct geometrical arrangement, as determined by experimental data or the prediction of VSEPR theory. 

The shapes of molecules are determined by actual experiments, not by theoretical considerations. But we do not want to have to memorize the shape of each molecule. Instead, we would like to be able to look at a Lewis structure and predict the shape of the molecule. Several models enable us to do this. One of the easiest to use is valence shell electron pair repulsion theory, which is often referred to by its acronym VSEPR (pronounced vesper ). As the name implies, the theory states that pairs of electrons in the valence shell repel each other and try to stay as far apart as possible. You probably remember this theory from your general chemistry class. The parts of VSEPR theory that... 

Use VSEPR theory to determine the geometry at each atom and the overall shape of the molecule. Then determine which bonds are polar based on the electronegativity differences of the atoms. Put in the directions for individual bond dipoles of these bonds. Estimate the result of vector addition of the bond dipoles to get the approximate direction for the overall dipole for the molecule. 

This chapter reviews molecular geometry and the two main theories of bonding. The model used to determine molecular geometry is the VSEPR (Valence Shell Electron Pair Repulsion) model. There are two theories of bonding the valence bond theory, which is based on VSEPR theory, and molecular orbital theory. A much greater amount of the chapter is based on valence bond theory, which uses hybridized orbitals, since this is the primary model addressed on the AP test. 

The other approach to molecular geometry is VSEPR theory. This theory holds that the shapes of molecules are determined by the repulsion between electron pairs around a central atom. Consider the bonding angle between two hydrogen atoms in a water molecule. One would a expect a 90° angle if hydrogen formed two... 

An elementary, but quite successful, model for determining the shapes of molecules is the valence-shell electron-pair repulsion (VSEPR) theory, first proposed by Sidgewick and Powell and popularized by Hillespic. The local arrangement ol atoms around each multivalent center in the molecule can be represented by... 

According to the VSEPR theory, the shape of a molecule is determined by the valence electrons surrounding the central atom. For example, examine the Lewis structure for CO2. 

The VSEPR theory predicts the three-dimensional shapes of molecules. It is based on simple electrostatics—electron pairs in a molecule will arrange themselves in such a way as to minimize their mutual repulsion. The steric number determines the geometry of the electron pairs (linear, trigonal pyramidal, tetrahedral, and so forth), whereas the molecular geometry is determined by the arrangement of the nuclei and may be less symmetric than the geometry of the electron pairs. 

Finally, water, H2O, has steric number 4 with two shared pairs and two unshared pairs on the oxygen atom. VSEPR theory predicts a bent structure, as a subcase of tetrahedral structure, with angles significantly less than the tetrahedral value of 109° due to repulsion between the two unshared pairs and the bonding pairs. Experimentally determined bond angles of 104° verify this prediction. 

Discuss the nature of the bonding in the nitrite ion (NO2). Draw the possible Lewis resonance diagrams for this ion. Use the VSEPR theory to determine the steric numbeg the hybridization of the central nitrogen atom, and the geometry of the ion. Show how the use of resonance structures can be avoided by introducing a de-localized 77 MO. What bond order does the MO model predict for the N—O bonds in the nitrite ion ... 

Apply the VSEPR theory to determine the arrangement of the regions of high electron density (the electronic geometry) about the central atom (Section 8-2 Tables 8-1 and 8-4). 

An important property of covalent molecules is that these covalent bonds have directional properties, and the molecules have three-dimensional shape. What determines this shape is the number of electron pair bonds in the valence shell configuration of the central atom (Figure 6.1), about which the shape of the molecule is described. The VSEPR theory... 

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