For each pair of solids, determine which solid has the higher melting point and explain why. (a) \(\mathrm{Fe}(s)\) and \(\mathrm{CCl}_{4}(s)\) (b) \(\mathrm{KCl}(\mathrm{s})\) or \(\mathrm{HCl}(\mathrm{s})\) (c) \(\mathrm{TiO}_{2}(\mathrm{~s})\) or \(\mathrm{HOOH}(\mathrm{s})\)

Metallic bonding is a type of chemical bonding that arises from the electrostatic attractive force between conduction electrons, in the form of an electron cloud of delocalized valence electrons, and positively charged metal ions. Imagine a structure where metal atoms release their outermost electrons to create a sea of electrons that surrounds a lattice of positively charged ions. This 'sea of electrons' is highly mobile and allows metals to conduct electricity and heat efficiently.

The strength of metallic bonding is one of the primary reasons that metals typically have high melting points. This is because a considerable amount of energy is required to break the bonds between the positively charged ions and the electron cloud. For example, iron, with its metallic bonding, has a higher melting point than molecular solids like carbon tetrachloride, which are bound by weaker forces.

Molecular solids are substances where the individual molecules are held together in a lattice or structured arrangement by intermolecular forces, rather than ionic or metallic bonds. The molecules in these solids are typically nonmetals and can be held together by varying types of intermolecular forces such as London dispersion forces, dipole-dipole interactions, or hydrogen bonding.

Since these forces are significantly weaker than the bonds in metallic or ionic solids, molecular solids usually have lower melting points. An example from the exercise is carbon tetrachloride (CCl4), where the individual molecules are held together by London dispersion forces, resulting in a comparatively low melting point.

Ionic solids are composed of ions held together in a rigid three-dimensional lattice structure by ionic bonds. These bonds are formed from the electrostatic attraction between oppositely charged ions, typically occurring between metal cations and nonmetal anions.

The lattice energy, which is the energy required to separate the ions, is a measure of the strength of these bonds, and thus, the melting point of an ionic solid. This energy is extensive due to the strong electrostatic forces of attraction between oppositely charged ions. Consequently, ionic solids, like potassium chloride (KCl) and titanium dioxide (TiO2), have high melting points, reflecting the strength of their ionic bonds.

Intermolecular forces are the forces of attraction or repulsion which act between neighboring particles (atoms, molecules, or ions). These include dispersion forces (also known as London forces), dipole-dipole interactions, and hydrogen bonds. They are the driving force behind the physical properties of molecular solids and liquids, including melting points, boiling points, and solubilities.

Dispersion forces are the weakest intermolecular force and arise from temporary dipoles in molecules. Dipole-dipole interactions are stronger and occur when polar molecules interact. Hydrogen bonds are the strongest of the intermolecular forces and occur when hydrogen is bonded to a highly electronegative atom like oxygen, nitrogen, or fluorine. Every different type of intermolecular force considerably affects the melting points of molecular solids, like those between hydrogen chloride (HCl) molecules.

Ionic bonds are one of the primary types of chemical bonds that occur between atoms with a significant difference in electronegativity. This type of bond involves the transfer of electrons from one atom to another, resulting in a cation (positively charged) and an anion (negatively charged). The ionic bond is the attractive force that holds these oppositely charged ions together in an ionic compound.

The strength of an ionic bond is a major factor in determining a compound's melting point. Ionic compounds, like KCl and TiO2 mentioned in the exercise, require a lot of energy to overcome the strong electrostatic forces between the ions, therefore, they have high melting points compared to molecular solids which are bound by intermolecular forces.