Predicting Geometry Using VSEPR Theory

Predicting Geometry Using VSEPR Theory Predict the electron and molecular geometry of PCI3. Predict the electron and molecular geometry of the [N03] ion.  

Draw a Lewis structure for the molecule. SOLUTION PCI3 has 26 electrons. SOLUTION [NOs] has 24 electrons.  

Determine the total number of electron groups around the central atom. 

Lone pairs, single bonds, double bonds, and triple bonds each count as one group. 

The central atom (N) has three electron groups (the double bond counts as one group). 

---

Methane, CH, has four hydrogen atoms bonded to a central carbon atom. Ammonia, NH3, has three hydrogen atoms bonded to a central nitrogen atom. Using VSEPR theory, predict the molecular geometry of each compound. 

Then predict the geometry around each atom using VSEPR theory. 

Use VSEPR theory to predict the geometries. Remember that multiple bonds count as one pair of electrons for the purpose of VSEPR theory. 

Use VSEPR theory to determine the geometry of the molecule. Assign bond dipoles to any polar bonds. Predict the overall dipole moment by estimating the result of vector addition of the bond dipoles. 

Valence shell electron pair repulsion theory (VSEPR) can be used to predict the shapes of molecules. According to this theory, the geometry of a molecule is such that the valence-electron pairs of the central atom are kept farthest apart to minimize the electron repulsions. Again, you have to view molecules in terms of Lewis structure so that the shape of the molecules can be predicted with the VSEPR theory. 

PRACTICE PROBLEM 1.27 Use VSEPR theory to predict the geometry of each of the following molecules and ions ... 

Predict the geometry of the following molecules using VSEPR theory (i) BFj (ii) CX l ... 

Use VSEPR theory to predict the molecular geometries of the molecules whose Lewis structures are given below. 

When VSEPR theory is used to predict molecular geometries, double and triple bonds are treated identically to single bonds as a single electron group, i.e. as a single place where you can find electrons. 

The Cl—F and Cl—Cl bonds in the cation are then formed by the overlap of the half-filled sp3 hybrid orbitals of the central chlorine atom with the half-filled p-orbitals of the terminal Cl and F atoms. Thus, by using sp3 hybridization, we end up with the same bent molecular geometry for the ion as that predicted by VSEPR theory (when the lone pairs on the central atom are ignored)... 

Molecular geometry, the arrangement of atoms in three-dimensional space, can be predicted using the VSEPR theory. This theory says the electron pairs around a central atom will try to get as far as possible from each other to minimize the repulsive forces. 

VSEPR) (Section 1.10) A theory that is used to predict geometry based on the principle that pairs of electrons in the valence shell of an atom repel each other and try to stay as far apart as possible. 

Using the principles of VSEPR theory, you can predict the geometry around any atom in any molecule, no matter how complex. Enanthotoxin is a poisonous compound isolated from a common variety of hemlock grown in England. Predict the geometry around the indicated atoms in enanthotoxin. 

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 ... 

How are double and triple bonds treated when the VSEPR theory is used to predict molecular geometry How is a single unshared electron treated ... 

Valence bond theory is one of the two quantum mechanical approaches that explain bonding in molecules. It accounts, at least qualitatively, for the stability of the covalent bond in terms of overlapping atomic orbitals. Using the concept of hybridization, valence bond theory can explain molecular geometries predicted by the VSEPR model. However, the assumption that electrons in a molecule occupy atomic orbitals of the individual atoms can only be an approximation, since each bonding electron in a molecule must be in an orbital that is characteristic of the molecule as a whole. 

VSEPR stands for valence shell electron pair repulsion. VSEPR theory can be used to predict actual geometries of molecules and composite ions. To be more precise it is a matter of determining bond directions and angles from the central atom in a molecule or composite ion to the other atoms. VSEPR theory can very shortly be formulated as follows ... 

When we are to determine how many electron groups that surround an atom, the Lewis structure can be of great help (see the previous section 2.23 Lewis structure). From the Lewis structure of a given molecule you can simply count how many bonds and lone pairs that surround an atom. That way you have the number of electron groups. The VSEPR theoiy tells us that these electron groups will be placed as far apart as possible. In the following example we will use the VSEPR theory to predict the molecular geometries of a water molecule and a carbon dioxide molecule. That way we will discover why a carbon dioxide molecule is linear and why a water molecule is V-shaped. 

Use the principles of VSEPR theory and molecular geometry to predict relative melting points, boiling points, and solubilities of compounds. 

---