Syllabus Problem 2D 19

[nicole_ershaghi 3F]

Could someone walk me through the process of this problem: Use the covalent radii to calculate the bond lengths in the following molecules. Account for the trends in your calculated values: (a) CF4 ; (b) SiF4 ; (c) SnF4.

[Ellie_Keenan_2A]

In order to solve this problem, you need to use the chart labeled Figure 2D.11 in the textbook. Using this chart, you can find the atomic radii of each atom. For example, for the first one (CF4), the radius of a Carbon single bond is 77 and the radius of a Fluorine single bond is 58. Adding these two values together gives the bond length for this bond.

[Erika Patel 3I]

Figure 2D.11 gives you the covalent radii of each atom in these structures. For each of these, you have the central atom (C, Si, or Sn) bonded to 4 fluorine atoms. Therefore, you know that your bonds are going to be C--F, Si--F, and Sn--F. To find the bond length, you simply add the radii of the central atom to the radii of the fluorine atom. So for C--F, you would add 77+58 to get 135 pm. The bond length should increase as the central atom gets further down the periodic table. This is because the atomic radius of the atom is larger since there are more orbital shells and shielding between electrons expanding the structure. Therefore, the distance between the two atoms would be greater.