What are the factors affecting the melting point of the substance?

Answer 1

There are basically two types of bonding in substances that affect the boiling point. Some compounds are composed of extensive networks of atoms held together by either ionic or covalent bonds. These network substances have very high melting and boiling points. NaCl is an example of an ionic network and SiO2 is an example of a covalent network.

The key factors that affect the boiling points of molecular compounds are the intermolecular forces which attract one molecule to another.

For covalent compounds these intermolecular forces are called van der Waals forces and consist of hydrogen bonding, dipole-dipole attraction, and London dispersion forces. Hydrogen bonding is usually stronger than dipole-dipole interactions. London dispersion forces, often weaker forces, are found between all molecules, even if other van der Waals forces are present.

The boiling point of a solution is also affected by the ambient pressure. Boiling occurs at a temperature where the vapor pressure of the liquid is equal to the ambient pressure.

The third thing that affects the boiling point of a solution is any substance that is dissolved in the liquid. The more particles (ions or molecules) there are dissolved in the solution, the higher the boiling point.

Answer 2

Entirely different things affect the melting points of covalent compounds and ionic compounds.

The melting points of covalent compounds are affected by which intermolecular force affects it and how strong they are: The intermolecular forces are: London forces, dipole to diploe forces and hydrogen bonding. Which ones are happening depends on the molecule. You'll have to research each force to understand how it works.

For ionic compounds it is due to charge density of either the anion or the cation: which is the relative charge/ionic radii. A greater charge density means a higher boiling point.

Answer 3

Both pressure and the presence of a catalyst will reduce the melting point of an object. Most melting points are given at 1 ATM (the pressure of Earth's atmosphere at sea level) without the aid of a catalyst.

Answer 4

The dominant factor is intermolecular forces

Answer 5

1-impurities present, 2-pressure.