Intermolecular Forces & Physical Properties Concept 1

Jules Bruno
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in this video, we're gonna take a look at the direct relationship between the inter molecular forces and physical properties. Now recall that physical properties are measurable and observed. The senses that describe the states of matter. We're going to say the inter molecular forces themselves are just the attractive forces that exists between molecules and influence these physical properties. Now, when we say direct relationships realize that under direct relationships, we're gonna say the stronger the inter molecular force than the greater the physical property. And the four physical properties that we will observe are boiling point melting point. Uh surface tension and viscosity for the first one we deal with boiling point. Now, boiling point is just the temperature where a liquid and a gas are in equilibrium with each other. The liquid can get vaporizes into a gas and the gas can condense down into a liquid. So boiling point is just the equilibrium between these two states. And we're gonna say, the stronger the inter molecular force than the greater the boiling point. Next we have melting point melting point is the temperature or a solid and a liquid are in equilibrium going from a solid to a liquid that involves melting or fusion going from a liquid to a solid is freezing. The greater the inter molecular force than the higher the melting point. Next we have surface tension Surface tension is just a measure of attractive forces on a liquid surface. So, just imagine that below the surface itself, we have water molecules. These water molecules are hydrogen body into one another. This causes a strong attraction between them so much, in fact, that there's a cohesive force that results on the top of the water. This kind of creates a false floor for certain insects to be able to walk across the water. Okay, so this is the phenomenon that insects are an insects take advantage of in order to cross over bodies of water and then finally we have viscosity. Viscosity may not be as known as the other three. We're gonna say at constant temperature, Viscosity is just the resistance. So flow for a substance. So you might have heard a substance being very viscous, that means it moves very slowly. Thinking of something that's very viscous honey, honey doesn't move very quickly. It's a viscous substance. Water on the other hand, it moves pretty quickly very easily. So water has a low viscosity. Now, we're gonna say here, the greater viscosity than the slower the movement. Okay, so it deals with time. Now, how could I how could I reduce the viscosity of a substance? I can introduce heat. So let's say that I heat up some of this honey. If I heat it up enough, I can help make it flow a lot faster. So we can say here that if I increase my temperature, I could help to decrease my viscosity and we're gonna say just like the other three. Before it, the stronger the inter molecular force, the greater the viscosity