Which solid in each pair has the higher melting point and why?
a. TiO₂(s) or HOOH(s)
b. CCl₄(s) or SiCl₄(s)
c. Kr(s) or Xe(s)

Verified step by step guidance

1. Identify the type of forces involved: Both krypton (Kr) and xenon (Xe) are noble gases, and in their solid forms, they are held together by London dispersion forces, which are a type of van der Waals force.
2. Understand the relationship between atomic size and dispersion forces: London dispersion forces increase with the size of the electron cloud, which is related to the atomic size.
3. Compare the atomic sizes: Xenon (Xe) has a larger atomic size compared to krypton (Kr) because it is located further down the group in the periodic table.
4. Relate atomic size to melting point: Since xenon has a larger atomic size, it has stronger London dispersion forces compared to krypton. Stronger intermolecular forces generally lead to a higher melting point.
5. Conclude which has the higher melting point: Therefore, Xe(s) is expected to have a higher melting point than Kr(s) due to its larger atomic size and stronger dispersion forces.

Key Concepts

Intermolecular Forces

Intermolecular forces are the attractions between molecules that influence physical properties such as melting and boiling points. In solids, these forces can include van der Waals forces, dipole-dipole interactions, and hydrogen bonding. The strength of these forces determines how much energy is required to break them apart, thus affecting the melting point.

Atomic Size and Mass

Atomic size and mass play a significant role in determining the melting points of solids. Larger atoms generally have more electrons, which can lead to stronger van der Waals forces due to increased polarizability. In the case of noble gases like Kr and Xe, the larger atomic size of xenon contributes to a higher melting point compared to krypton.

Noble Gases and Their Properties

Noble gases are characterized by their complete valence electron shells, making them chemically inert. However, they still exhibit physical properties influenced by their atomic structure. Among noble gases, melting points increase with atomic number due to greater van der Waals forces, which is relevant when comparing the melting points of solid krypton and xenon.