VSEPR theory ammonia

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. 

The VSEPR theory of the ammonia molecule starts with the nitrogen atom (2s22p3), to which is added the Is electrons from the three hydro-... 

The same kind of sp3 hybridization that describes the bonds to carbon in the tetrahedral methane molecule also describes bonds to nitrogen in the trigonal pyramidal ammonia molecule, to oxygen in the bent water molecule, and to all other atoms that VSEPR theory predicts to have a tetrahedral arrangement of four charge clouds. 

Again, the four electron pairs will arrange themselves as far apart as possible because of electrostatic repulsion, and the molecular structure will be like that of ammonia shown in Figure 1.266, the lone pair of electrons being in an orbital directed toward one corner of the tetrahedron. According to the VSEPR theory, lone-pair electrons are less localized, i.e, occupy more volume than the bond pairs. A lone pair therefore exerts a greater repulsion on the bond pairs than the bond pairs do on each other. 

Problem 3.19. What does VSEPR theory predict for the structure of ammonia ... 

Explain the shape of ammonia molecule on the basis of VSEPR theory. 

Ammonia, NHg, and water, H2O, are examples of molecules in which the central atom has both shared and unshared electron pairs (see Figure 5.4 on the next page for their Lewis structures). How does VSEPR theory account for the geometries of these molecules ... 

Next we will consider molecules that have both bonded and nonbonded pairs of electrons in the valence shell of the central atom. Water and ammonia have four electron pairs around the central atom. Some of the electron pairs in water and ammonia are bonded to hydrogen atoms, but the central atom also has unshared electron pairs. VSEPR theory describes the distribution of bonded and nonbonded electron pairs. However, molecular structure is defined by the positions of the nuclei. The four pairs of electrons in both water and ammonia are tetrahedrally arranged around the central atom. Water, with only three atoms, is angular, and ammonia, with four atoms, is pyramidal (Figure 1.7). 

Practice Problem A Predict whether iodine (L) is more soluble in liquid ammonia (NH3) or in structure and applying the VSEPR theory [M4 Section 9.2]. 

Ammonia, NH3. The nitrogen atom and the ion have the same number of electrons. They can combine with three hydrogen atoms to give NH3 and H30, respectively. In both cases, VSEPR theory predicts a pyramidal shape. 

The rules and principles of molecular geometry accurately predict the shapes of simple molecules such as methane (CH4), water (H2O), or ammonia (NH3). As molecules become increasingly complex, however, it becomes very difficult, but not impossible, to predict and describe complex geometric arrangements of atoms. The number of bonds between atoms, the types of bonds, and the presence of lone electron pairs on the central atom in the molecule critically influence the arrangement of atoms in a molecule. In addition, use of valance shell electron pair repulsion theory (VSEPR) allows chemists to predict the shape of a molecule. 

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