Carbon tetrachloride molecular shape

When we look at the overall molecular structure of carbon tetrachloride, the net vectorial force in this molecule is zero as its shape is symmetrical so CC14 is a non-polar molecule. 

Compare two molecules with the same molecular shape CCI4 and CCI3H. Since the polarity of the C—Cl bond is different from that of the C—H bond, the polarities of these two molecules are different. The CCI4 molecule is symmetrical about any axis joining the two atoms of the C—Cl bond. The polarities of the C—Cl bonds counteract one another. Thus, the carbon tetrachloride molecule is non-polar. In the case of CCI3H, the polarity of the H — Cl bond is different from that of the three C—Cl bonds. Thus, the molecule is polar. 

In a review of the motions of guest molecules in hydrates, Davidson (1971) indicated that all molecules between the sizes of argon (3.8 A) and cyclobutanone (6.5 A) can form si and sll hydrates, if the above restrictions of chemical nature are obeyed. Ripmeester and coworkers note that the largest simple structure II former is tetrahydropyran (THP) (C5H10O) with a van der Waals diameter of 6.95 A (Udachin et al., 2002). Closely following THP are m- and p-dioxane and carbon tetrachloride, each with a molecular diameter of 6.8 A (Udachin et al., 2002). Molecules of size between around 7.1 and 9 A can occupy sH, provided that the below shape restrictions are obeyed and a help gas molecule such as methane is included. 

In these two cases the dipole arrows cancel each other out because of the shape of the molecules. The linear shape of the molecule of carbon dioxide puts the dipole arrows in opposite directions to counterbalance each other. The same holds true for the tetrahedral molecular geometry found in carbon tetrachloride. Despite having polar bonds, these two molecules are nonpolar. There is no overall dipole moment in these molecules because the dipole arrows are of the same magnitude but lie in opposite directions in the molecule. This counterbalance causes the molecule to be nonpolar. 

Just because elements have the same molecular structure doesn t mean they have the same symmetry. For example, if you take the methane molecule from Figiffe 7-4 and sum up all the symmetry elements, you find four Cj and three C2 axes, as well as six o planes. If you swap all the hydrogen atoms with chlorine atoms (CCI4 or carbon tetrachloride), your new molecule has the exact same symmetry. However, if you swap only three of the hydrogen atoms with chlorine atoms (CHCljOr chloroform), your symmetry decreases because the number of symmetry elements decrease in number (CHClj has only one Cj axis and only three o planes). So even though CH, CCl, and CHClj are all tetrahedral in shape, onty CH and CCl have the same symmetry. 

Carbon tetrachloride (CCI4) is nonpolar because the four C—Cl polar bonds are identical, and since these bonds emanate from the center to the corners of a tetrahedron in the molecule, their polarities cancel one another. Methane has the same molecular structure and is also nonpolar. We will discuss the shapes of molecules later in this chapter. 

In chloromethane, the tetrahedral shape is clear, but there is only one polarized bond and the dipole for the molecule is easily predicted. In dichloromethane, however, there are two bond moments, and the dipole for the molecrde is the vector sum of these two bond moments (magnitude and direction). The dipole is shown. For trichloromethane (chloroform), the magnitude and direction of the three polarized C-Cl bonds lead to the molecular dipole moment shown. Carbon tetrachloride is interesting. There are four C-Cl bonds with equal bond polarization and dipole moments. Summing all four dipole moments for the bonds, which are directed to the corners of a regular tetrahedron, leads to a dipole moment of zero because the magnitudes of the individual bond moments cancel. 

Solution (a) Bromine is more soluble in benzene. (b) Sodium iodide is more soluble in water. (c) Carbon tetrachloride is more soluble in benzene. (d) Formaldehyde is more soluble in water. Think About It Remember that molecular formula alone is not sufficient to determine the shape or the polarity of a polyatomic molecule. It must be determined... 

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