Now the most fundamental distinction between solids is that they can be classified as either crystalline or amorphous solids. Now when we say crystalline solid, we're going to say here that's atoms, ions, or molecules that have highly ordered arrangements throughout. And amorphous solids are particles that are randomly arranged throughout with no discernible pattern.
Now when we say crystalline solids, we're referring to ionic solids, molecular solids, covalent network solids, and metals. Now here we're going to say for ionic solids the smallest unit is the ionic part and that's because its electrostatic forces are the attraction between a positive ion and a negative ion. Remember we know the definition of ionic compounds is a cation connected to an anion. That cation can be a metal or ammonium ion. That anion is just some non-metals.
Now we can say here also their properties are that ionic solids tend to be brittle and yet hard. And we're going to say here that they have high melting points. A good example is if we're looking at solid sodium chloride for our ionic compound.
Molecular solids, their smallest unit is the molecule. Their electrostatic force is the intermolecular forces. We're going to say here that they have soft textures to them. We're going to say they have low to moderate melting points. A good example of a molecular solid that we can think of is ice, which is just H2O solid.
Covalent network solids, their smallest unit is the atoms. They are covalent bonds for their electrostatic force. Now if you want to understand the hardest materials in nature, you're referring to the covalent network solids. They have very hard textures and they have very high melting points, even higher than our ionic solids. A great example, one of the hardest natural substances in nature, is diamonds. Remember, diamonds are just a form of carbon, so carbon diamond. But that's not the only form that carbon can take within nature. It could also take carbon graphite as well.
Metals, of course, are composed of metal atoms. We're going to say here that we're dealing with metallic bonds, and that's just the pooling of electrons on the surface of your metal. We're going to say they can be lustrous, which means that they are shiny. They can be from soft textures with sodium to hard textures like titanium. We're going to say they also have high melting points, so here an example is the ones we gave, sodium or titanium.
Finally, we have our amorphous solids, which are different from all these other crystalline solids. Here they are composed of atoms, ions, molecules, or what we'll refer to as polymers. When we say polymers, we're talking about different forms of plastics. Because they don't have a discernible pattern, they kind of resemble some of the crystalline solids we mentioned above. So that means their electrostatic force can be any of the ones mentioned above. Because of their weird nature and composition, they tend to not have a distinct melting point, and what's really weird about them is that they're solids, but they're able to flow, so that's not a normal thing. The ability to flow is usually reserved for liquids and gases.
Now a great example here you could say is glass or tar. So tar, the material that we use on roads, is an example of an amorphous solid. And if you can understand what tar looks like, black sticky stuff, it's able to flow. All right, so these are the different types of crystalline solids and how they're different from an amorphous solid.
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