Of each pair of solids, which one has the higher melting point?

a) HCl and KCl
b) Cu and Kr.

Can you please explain? How do you know the melting point? Is it the type of intermolecular force that they have?

thanks!

There are a number of things to look at. For a, HCl is largely a covalent bond (although polar covalent) while KCl is an ionic solid. Ionic solids melt higher than most covalently bonded materials because the ionic solids must break the crystal lattice bonds. Cu has metallic bonding and Kr has only dispersion forces.

Ah, the battle of the melting points, let the showdown begin!

a) HCl and KCl:

In this corner, we have HCl, also known as hydrogen chloride. It's a linear molecule composed of a hydrogen atom and a chlorine atom. And in the other corner, we have KCl, otherwise known as potassium chloride. This compound consists of a potassium atom and a chlorine atom.

Now, which one has the higher melting point? Drumroll, please... and the winner is KCl!

Potassium chloride reigns supreme in the melting point department because it has stronger intermolecular forces than hydrogen chloride. KCl has ionic bonds, which are quite strong, thanks to the attraction between the positively charged potassium ion and the negatively charged chloride ion. On the other hand, HCl has polar covalent bonds, which are not as strong as the ionic bonds found in KCl. So, in the battle for the higher melting point, KCl takes the victory!

b) Cu and Kr:

In this corner, we have Cu, our friendly copper, known for its shiny appearance and great conductivity. And in the other corner, we have Kr, also known as krypton, an inert gas of the noble gases family.

Now, who will take the win in the battle of melting points? Wait for it... and the winner is Cu!

Copper (Cu) has a much higher melting point compared to krypton (Kr). Copper exhibits metallic bonding, where the metal atoms are arranged in a regular pattern and share a pool of delocalized electrons. These delocalized electrons create a strong binding force, resulting in a high melting point.

Krypton, on the other hand, is a noble gas that exists as individual atoms. These atoms have weak London dispersion forces holding them together, which are much weaker than metallic bonding. As a result, krypton has a significantly lower melting point compared to copper.

So, there you have it! The melting point battle is over, and the champions are KCl and Cu, respectively. Interactions like intermolecular forces and the type of bonding play a vital role in determining the melting points.

To determine which solid has a higher melting point in each pair, we need to consider the intermolecular forces present in each substance.

a) HCl and KCl: HCl is a molecular solid, and KCl is an ionic solid. In molecular solids, the intermolecular forces are primarily van der Waals forces. In ionic solids like KCl, the intermolecular forces are electrostatic attractions between oppositely charged ions. Generally, ionic solids have higher melting points compared to molecular solids because the electrostatic forces between ions are stronger than the van der Waals forces. Therefore, KCl has a higher melting point than HCl.

b) Cu and Kr: Cu is a metallic solid, and Kr is a noble gas in the gaseous state. Metallic solids have a unique type of bonding called metallic bonding, where positive metal ions are held together by a sea of delocalized electrons. Noble gases, on the other hand, are monatomic substances that exist as individual atoms. Metallic solids generally have higher melting points than noble gases because the metallic bonding is stronger than the weak intermolecular forces present in noble gases. Therefore, Cu has a higher melting point than Kr.

The melting point of a substance is related to the strength of the intermolecular forces. Stronger intermolecular forces require more energy to break, resulting in a higher melting point.

To determine which solid has a higher melting point in each pair, we need to consider the type of intermolecular forces present in the substances. The strength of these intermolecular forces affects the energy required to break the bonds and convert the solid into a liquid state.

In the case of HCl and KCl, both are ionic compounds composed of positively charged ions (cations) and negatively charged ions (anions). The intermolecular forces holding them together are called ionic bonds. These bonds are quite strong, requiring a significant amount of energy to break them. Therefore, both HCl and KCl have relatively high melting points. However, KCl has a slightly higher melting point compared to HCl because potassium and chloride ions have stronger attractive forces between them due to stronger ionic charges.

Cu (copper) is a metallic solid, and Kr (krypton) is a noble gas. Metals have metallic bonds, which are a type of strong intermolecular force. Noble gases, on the other hand, have weak intermolecular forces called London dispersion forces. Although copper has a higher melting point compared to krypton, it is essential to note that copper's high melting point is primarily due to its strong metallic bonding and not the intermolecular forces alone.

To determine melting points experimentally, chemists typically use techniques such as differential scanning calorimetry (DSC) or data available in chemical databases. These methods provide accurate measurements of melting points for various substances under specific conditions.

In summary, the type and strength of intermolecular forces present in solids determine their melting points. Ionic compounds tend to have higher melting points than noble gases, while metals generally have high melting points due to metallic bonding.