Substances’ physical properties get affected by attractive forces existing between molecules. It’d be interesting to find out exactly what happens to these physical properties as the strength of intermolecular forces increases?
- Some of the Physical Properties of Substances Affected by Intermolecular Forces
- Different types of IMF or intermolecular forces
- How do these affect the physical properties of substances? Let’s look at a few examples
- Wrapping it up
By definition, intermolecular forces (or IMF) are what mediates molecular interaction in the matter, and these forces may include repulsion or attraction between molecules and their neighboring particles (ions and atoms being examples).
Some of the physical properties of substances affected by these intermolecular forces include melting point, viscosity (the ability of a fluid to flow), evaporation, boiling point, freezing point, and vapor pressure.
Just like there are numerous options for substances you’d use to hold together a broken glass flower vase- glue, adhesive tape- so are there different IMF forces. And, yes, they too differ in strength-wise much the same way. The four are here-below noted:
1. Ionic Forces
Ions are bonded mainly by electrostatic forces making ionic solids. Here, the great attraction between opposite charges, form the strongest IMF forces.
2. Dipolar Forces
These are attractions between poles or “ends” of molecules that give them partial opposite charges causing intermolecular attractions.
The other two are hydrogen bonding and induced dipole forces.
a. Melting, Boiling, and Vaporisation
As IMF increases from low to high in substances, it causes them to have different physical strengths or weaknesses. For instance, a substance with very high IMF forces will have a higher melting and boiling point compared to others with lower intermolecular forces.
A small iron rod has very high ionic forces thus high IMF and will thus melt at considerably high temperatures compared to your standard soldering wire. As ions in iron strongly attract one another, it is very hard to melt such a rod compared to soldering wire. An aluminum
the strip will not melt as easily as would do candle wax.
The same case applies to ease of evaporation in compounds. The higher the IMF, the lower the rate of their evaporation. Compare for instance tap water and milk. Which one would be harder to evaporate?
The higher the IMF, the lower the rate of their evaporation.
Have you ever tried to pour out grease from a container? It resists flowing out. How about milk from a glass? Very easy to pour out. The difference between these two fluid’s ability or inability to flow out freely is their viscosity. IMF when high in a liquid leads to higher resistance to flow (that is, greater viscosity).
Not to be confused with intramolecular forces, intermolecular forces (IMF) are what bonds molecules together in a given substance. They play a very important role in affecting some matter’s physical properties.
As a general rule, the higher the IMF (whether ionic, dipolar, hydrogen bonding or induced bipolar) forces, the higher the melting, boiling and vaporization points of a given substance. Also, viscosity in liquids is higher where IMF is high and vice versa.