chemistry-intermolecular forces-predicting melting point
Without intermolecular forces holding molecules together we would not exist. .. To investigate boiling point and to determine the relation between boiling point. Intermolecular forces exist between molecules and influence the physical When the temperature reaches 0oC, the melting point of ice, further addition of heat. In this lesson we will review what intermolecular forces are and how they will affect physical properties such as boiling point, freezing point.
In order to predict the forces acting we need to know if the molecule: Finally we need to know the number of electrons in the molecule in order to determine its relative size.
Melting and boiling temperatures of substances are an indication of the relative strength of their intermolecular bonds, the stronger the intermolecular bonds the greater the melting temperature of the substance.
Consider the simple diagram on the right. It is only used as a guide to sort molecules of the same size. As we follow the diagram downwards the substance furthest to the left has the highest melting temperature.
- Covalent bonds
- Intermolecular Forces and Physical Properties
- Intermolecular Forces
Keep in mind this a simple method and overlap does occur between symmetrical molecules and asymmetrical molecules. A prime example is iodine I2 which exists as a solid at room temperature due to its size which generates sizeable dispersion forces.
The Four Intermolecular Forces and How They Affect Boiling Points
Melting and boiling points are both indicators of the strength of inter-molecular bonding. Solid carbon dioxide and ice water are placed in a sealed vessel and heated.
Which molecular substance has the highest melting point? Since water is the molecular substance on the left it has the highest melting point. Consider methane CH4 and carbon dioxide CO2.
Which has the highest melting point? The Velcro junctions will fall apart while the sewed junctions will stay as is.
Effect of Intermolecular Forces on Physical Properties
The attachment created by Velcro is much weaker than the attachment created by the thread that we used to sew the pairs of towels together. A slight force applied to either end of the towels can easily bring apart the Velcro junctions without tearing apart the sewed junctions.
Exactly the same situation exists in molecules. Just imagine the towels to be real atoms, such as hydrogen and chlorine.Intermolecular Forces - Hydrogen Bonding, Dipole-Dipole, Ion-Dipole, London Dispersion Interactions
These two atoms are bound to each other through a polar covalent bond—analogous to the thread. Each hydrogen chloride molecule in turn is bonded to the neighboring hydrogen chloride molecule through a dipole-dipole attraction—analogous to Velcro. The polar covalent bond is much stronger in strength than the dipole-dipole interaction.
The former is termed an intramolecular attraction while the latter is termed an intermolecular attraction. Figure of towels sewn and Velcroed representing bonds between hydrogen and chlorine atoms, illustrating intermolar and intramolar attractions So now we can define the two forces: Intramolecular forces are the forces that hold atoms together within a molecule.
Intermolecular forces are forces that exist between molecules.
Figure of intermolecular attraction between two H-Cl molecules and intramolecular attraction within H-Cl molecule Types of intramolecular forces of attraction Ionic bond: This bond is formed by the complete transfer of valence electron s between atoms. It is a type of chemical bond that generates two oppositely charged ions.