Molecular shape tetrahedral arrangement

Step 3 The geometric arrangement of the electron groups is tetrahedral. Step 4 For 3 BPs and 1 LP, the molecular shape is trigonal pyramidal. 

Figure 3-17. The molecular configuration of zirconium borohydride, Zr(BH4)4, in two interpretations but described by the same polyhedral shape. Left, the zirconium atom is directly bonded to the four tetrahedrally arranged boron atoms [28] Right the zirconium and the tetrahedrally arranged boron atoms are not bonded direcdy their linkage is established by four times three hydrogen bridges [29].

The isoelectronic molecules CH4, NH3, and H2O (Figure 3-10) illustrate the effect of lone pairs on molecular shape. Methane has four identical bonds between carbon and each of the hydrogens. When the four pairs of electrons are arranged as far from each other as possible, the result is the familiar tetrahedral shape. The tetrahedron, with all H—C — H angles measuring 109.5°, has four identical bonds. 

Explain why the atoms in the CH4 molecule are arranged with a tetrahedral molecular shape. 

Molecular Shapes with Four Electron Groups (Tetrahedral Arrangement)... 

Name all the molecular shapes that have a tetrahedral electron-group arrangement. 

Figure 11.5 shows the bonding in other molecular shapes with the tetrahedral electron-group arrangement. The trigonal pyramidal shape of NH3 arises when a lone pair fills one of the four sp orbitals of N, and the bent shape of H2O arises when lone pairs fill two of the sp orbitals of O. 

See Practice Problem Exercise 12.4) The four pairs of electrons around the sulfur require a tetrahedral arrangement. In this case two pairs are shared with hydrogen atoms, leaving two lone pairs. Thus the molecular structure is bent or V-shaped (case 5 in Table 12.4). 

The VSEPR model, simple as it is, does a surprisingly good job at predicting molecular shape, despite the fact that it has no obvious relationship to the filling and shapes of atomic orbitals. For example, we would like to understand how to account for the tetrahedral arrangement of C—H bonds in methane in terms of the 2s and 2p orbitals of the central carbon atom, which are not directed toward the apices of a tetrahedron. How can we reconcile the notion that covalent bonds are formed from overlap of atomic orbitals with the molecular geometries that come from the VSEPR model ... 

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