Intermolecular forces explained

intermolecular

forces

, we will see how

intermolecular

forces

affect the physical properties of molecules and we will also see how we identify different types of intermolecular forces, so let's start with an example of water. Now water has a formula h2o which means that it is made up of water molecules, two hydrogen atoms and one oxygen atom and in the oxygen atom there are two lone pairs of electrons. Now remember that in the liquid state the particles or molecules are very close together and can move around each other, they are random. They are arranged but remain very close and those molecules are held together in a liquid state by attractive forces called intermolecular forces.

Intermolecular forces are always attractive, so you can imagine liquid water molecules moving around each other but also being attracted to each other. by these strong intermolecular forces that put inter means in the middle, for example, Intercity is a service that runs between cities, so it acts between molecules or forces that keep the molecules together in a liquid state, so if you imagine that you want to boil the water, spin it. In a gas we have to release the molecules. We call this change evaporation or boiling, but do not confuse the two. Boiling occurs at the boiling point, which would be one hundred degrees Celsius, while evaporation is a change from liquid to gas. below the boiling point and when the molecules enter the gaseous state, they fly freely in all directions with a lot of energy and occupy the entire available volume, they diffuse because they move randomly, but to enter this molecular state we have the freedom to overcome the forces intermolecular forces or act between molecules so we have to supply energy to the water to boil or evaporate we can say that boiling and evaporation in endothermic processes absorb energy from the environment and that the energies necessary to overcome intermolecular forces is attraction that was between the molecules, so let's look at these three types of intermolecular forces, then the first and weakest ones are called van der vowels and the W is pronounced as V, so the intermolecular forces of van der vowels are very weak.

Let's see how they occur in the case of a non-polar or aten molecule and this would be the strongest intermolecular force in action and the founding vale forces occur between any two atoms or molecules that have electron clouds, so basically everything in the molecular levels. attracted by these forces and it is because of their electron clouds that this intermolecular force occurs, so let's draw the electron clouds around: methane molecules for example, a blue line represents the electron cloud. Remember that it describes how electrons exist in these orbitals around atoms and them. We are a random system, so it is all about probability, so the electron density varies with time, for example if we have a small fluctuation in the electron density around hydrogen, you get a small Delta, which appears randomly and will repel electrons in nearby clouds. in molecules that will create a Delta plus and then we get this temporary attraction, so we can call it a temporary dipole induced dipole, which means that a temporary dipole induces or causes a dipole and an adjacent molecule.

The next type is called a permanent dipole, permanent dipole, so Now we're talking about dipoles that are just there in the molecules and not temporary random fluctuations and electrons and these things are there permanently and this is the Internet, it's a force between the molecules. polar, for example, hydrogen chloride molecules, so remember that chlorine is more electronegative. than hydrogen, which means it pulls the electrons in that covalent bond towards itself, the electron cloud is not evenly distributed around the molecule, there is more electron density in chlorine, so the hydrogen is left with a Delta plus charge and chlorines form a Delta minus charge, remember the opposites.

They attract each other, so in two different molecules there will be attraction between Delta plus in Delta, which will act to keep the molecules together. The third and final type of intermolecular force we will look at is the hydrogen bond now the term bond is a misnomer, it is not actually a proper bond, it is still weaker than covalent bonds but it is the strongest type of intermolecular force, but don't be confused by the name, it is not a real bond, it now acts between the lone pairs of fluorine, oxygen or nitrogen atoms. and very Delta positive hydrogen atoms and that is a strict definition so we will see how to apply it shortly, but let's take the example of hydrogen fluoride HF, it is a covalently bonded molecule and fluorine is the most electronegative element in the periodic table, so it actually pulled those electrons towards itself in the covalent bond let's also pop the lone pairs in the fluorine, this time you can see the lone pairs and it's a really big flat dipole that's actually pulling those electrons towards itself, it has a huge negative Delta charge on the fluorine coming off the very Delta plus hydrogen and that attraction between the Delta plus hydrogen and the lone pairs on the floor is called hydrogen bonding.

It is a very strong intermolecular force. So how are intermolecular forces calculated? Let's put together a flowchart and ask ourselves some questions. The first point is whether there are dipoles in the molecule and if we answer no, we are talking about a non-polar molecule, the strongest intermolecular force will be the vocal van der forces, but if there are dipoles, we must ask ourselves a few more questions. Are there fluorine, oxygen, or nitrogen atoms with lone pairs of electrons? Now, if we answer yes to that question, we will have to ask ourselves more questions. If we answer no, then the intermolecular forces, the permanent dipole, the permanent dipole, in words of love, if there is one. it is a dipole but there is no fo are in atoms with lone pairs and it will be a permanent dipole permanent dipole but if there is fo RM with lone pairs we want to ask if the hydrogen atoms are directly bonded within the molecule to those fo or n atoms now, yes we say yes, then it will be hydrogen bonds between the molecule, but if we say no, there are no hydrants directly attached to the FO or n, then its permanent dipole is permanent dipole, so you have these three types of intermolecular.

The force found the permanent dipole of the file, the permanent dipole and the hydrogen bond. If we use this flowchart, we can always calculate the type of intermolecular force in action, so let's take an example. Bromine B is two molecules. Now the bromine atoms are so electronegative to each other. They have the same attraction on electrons, so bromine is non-polar, which means that the strongest type of intermolecular force will be the van der Valles, there are no dipoles, let's look at another example of NH3 ammonia, like this The first question we will ask ourselves is: Are there dipoles, either because nitrogen is more electronegative than hydrogen.

Is there nitrogen for? There are n atoms. We have learned pairs, but nitrogen and hydrogen are directly bonded to nitrogen in the molecule. Yes, so our strongest type of intermolecular force. It's going to be a hydrogen bond, okay, taking the example of chloromethane ch3cl, are there dipoles in the molecule? Well, chlorine is more electronegative than carbon, so the answer is yes and there are atoms with lone pairs, no, and that's how it will end. being permanent dipole permanent dipole Delta minus the chlorines are attracted to the Delta plus the carbons, okay, take the example of water, you may already know that water molecules are attracted to hydrogen bonds, but let's take a look at why what we have Etha or in atoms. with lone pairs, yes, other hydrogen atoms bonded directly to fo.1, yes, then we will get hydrogen bonds acting between the Delta plus hydrogens and the oxygen lone pairs, okay, let's take another example, let's try something that is a alkane, now remember carbon.

Hydrogen bonds are non-polar, so ethane molecules and not polar molecules, are there dipoles? No, the strongest intermolecular force that holds the molecules of the Earth's spots together is a Van der Waals force, which is why ethane has such a low boiling point, even at room temperature, it is already a gas. well, let's look at another example of methane floor CH 3f, are there dipoles in the molecule? Yes, fluorines are more electronegative than carbon, so you have a dipole between carbon and fluorine and other Fon atoms with lone pairs. Yes, F has free pairs, but. Are there hydrogen atoms bonded directly to the F atoms?

No, so this is a permanent dipole, a permanent dipole, so this flow chart can really help you answer questions about intermolecular forces. I hope this has helped you. I hope to see you again.