Draw the Lewis structure of (a) \(\mathrm{CF}_{4}\), (b) \(\mathrm{SF}_{4}\), name the molecular shape, and indicate whether each can participate in dipole- dipole interactions.

When predicting the shape of a molecule, we rely on the Valence Shell Electron Pair Repulsion (VSEPR) theory. This theory posits that electron pairs around a central atom will position themselves as far apart as possible to minimize repulsion. Each pair, whether part of a bond or not, has a region of negative charge. By spreading out, these regions reduce the energy of the system.

VSEPR theory categorizes electron pairs into two groups: bonding pairs, which are shared between atoms, and lone pairs, which belong exclusively to one atom. The combination of bonding pairs and lone pairs determines the molecular geometry. For instance, the CF4 molecule has four bonding pairs and no lone pairs on the central carbon atom, leading to a tetrahedral shape, as all positions are equivalent and maximally spaced around the carbon atom.

Contrastingly, the SF4 molecule has four bonding pairs as well but also a lone pair on the sulfur atom. The presence of this lone pair distorts the shape, resulting in a see-saw geometry. The lone pair occupies more space than a bonding pair, causing the surrounding bonds to adjust their positions slightly, hence the 'see-saw' designation.

Molecular shape, also known as molecular geometry, significantly impacts a molecule's properties and reactivity. The three-dimensional arrangement of atoms in a molecule defines its geometry. As shown by our sample exercises, CF4 is tetrahedral, with the fluorine atoms symmetrically arrayed around the central carbon atom. This symmetrical arrangement is favored because it minimizes the repulsion between the electron pairs as per VSEPR theory.

On the other hand, SF4's see-saw shape is an example of what happens when a lone pair is introduced to the surrounding bonding pairs' dynamics. The geometry is not as symmetrical as that of a tetrahedral CF4 molecule. Understanding molecular shapes is crucial for predicting how molecules will interact with one another and their potential energy minima, which are important for visualizing reactions and understanding the physical properties of substances.

Dipole-dipole interactions occur between polarized molecules, where one end of the molecule carries a slight positive charge, and the other end carries a slight negative charge. This phenomenon is caused by the uneven distribution of electrons, which creates a dipole moment. CF4, being a nonpolar molecule due to its symmetry and equal distribution of charge, lacks a dipole moment and thus, cannot engage in dipole-dipole interactions. The electronegativity difference between Carbon and Fluorine is not great enough to create poles within the molecule.

SF4, in contrast, exhibits a clear see-saw shape and has polar bonds. The asymmetrical distribution of electrons due to the presence of the lone pair leads to a net dipole moment. As a result, SF4 can take part in dipole-dipole interactions. These interactions are significant because they influence the boiling points, melting points, and solubilities of substances. Molecules that can engage in dipole-dipole interactions often have higher boiling points due to the additional energy required to overcome these interactions during the phase change from liquid to gas.