Difference Between Crystalline And Amorphous Materials Pdf


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difference between crystalline and amorphous materials pdf

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Polymers are unlike other types of materials because of their high molecular weight. Molecular weight is the value used to express the size of a molecule.

Amorphous solid

These pranks work well because salt and sugar are almost indistinguishable by the naked eye: Both are crystalline solids with similar structures. Nonetheless, they have very different flavors, and they behave differently too. Differences arise from the different properties of the two crystals , including the atoms that compose them and the actual structure of the crystal itself. In this module we will explore different types of solids and discuss how their structures relate to their behavior.

From ancient Greece until the birth of modern chemistry in the 17th century, people may have been confused about what made salt and sugar so different. As scientists began identifying and characterizing elements in the 17th and 18th centuries, they would have been able to determine that salt is made of sodium and chlorine, while sugar consists of carbon, hydrogen, and oxygen, but they would probably still have wondered how such combinations of completely different elements lead to such similar-looking crystals.

In fact, salt was the first solid investigated by this method, called X-ray crystallography , which revealed a regular lattice of sodium and chlorine atoms. Applying X-ray crystallography to sugar reveals a similar but not identical well-ordered crystal Figure 3. Similarities in their crystal structure account for similarities in crystal appearance; however, the different types of atoms that make up each crystal and the different arrangements of the atoms account for the differences in behavior between the two solids.

X-ray crystallography has also become a critical tool in modern biology research , helping to reveal the double helix structure of DNA in the s see our DNA II: The Structure of DNA module and the structure of many simple and complex biological systems since that time.

Now that researchers can see this level of detail through X-ray crystallography and other methods , they can understand why some solids behave the way they do. And they can also use their understanding of the relationship between structure and behavior to design new and useful materials.

You may not think of salt and sugar as solids because when you see them in the kitchen they are such small particles. But each of these particles is as much a solid as a wooden table, a glass window, or a gold piece of jewelry. A solid is a collection of atoms or molecules that are held together so that, under constant conditions, they maintain a defined shape and size.

Solids, of course, are not necessarily permanent. Solid ice can melt to form liquid water at room temperature, and extremely high temperatures can be used to melt solid iron so it can be shaped into a skillet, for example.

Once that skillet is formed and cools back to room temperature, though, its shape and size will not change on its own, as opposed to molten metal, which can be made to drip and change shape by gravity and molds. Solids have constant shape and size because they are formed when the attractive forces between individual atoms or molecules are greater than the energy causing them to move apart.

See our States of Matter module for more about how solids differ from other states of matter. Salt and sugar are both crystalline solids. The other main category of solids is called amorphous. While crystalline solids are well ordered at the atomic level, with each atom or molecule inhabiting a specific point on a lattice , amorphous solids are disordered at an atomic level, with the atoms or molecules held together in a completely random formation.

Consider a game of checkers. A board carefully set up with a checker in each square is analogous to a crystalline solid, while an amorphous solid could be represented as a checker pieces randomly scattered across the board.

Quartz and glass are atomic-level examples of these two categories of solids. Quartz is a crystalline solid containing a high silicate SiO 2 content. If we were to examine the structure of quartz, we could see that the silicate subunits are arranged very precisely see Figure 4.

Glass, on the other hand, is an amorphous solid. Although its typical smooth, transparent appearance may make it seem like it must have a neat, organized microscopic structure, the opposite is true: The silicate units are unevenly scattered throughout the solid in a completely disordered fashion. Like quartz , glass has a very high silicate SiO2 content. The crucial difference between crystalline and amorphous solids is not what they are made of, but how they are made, and more precisely how their structures are arranged.

Quartz forms on a very slow, geological timescale so the atoms have time to achieve a highly ordered crystal structure, in which the atoms optimize the attractive forces and minimize the repulsive forces between them and which is therefore energetically favorable. Amorphous solids are often formed when atoms and molecules are frozen in place before they have a chance to reach the crystalline arrangement, which would otherwise be the preferred structure because it is energetically favored.

Crystal structure determines a lot more about a solid than simply how it breaks. Structure is directly related to a number of important properties, including, for example, conductivity and density , among others. To explain these relationships, we first need to introduce the four main types of crystalline solids — molecular, network, ionic, and metallic — which are each described below.

Individual molecules are composed of atoms held together by strong covalent bonds see our Chemical Bonding module for more about covalent bonding. To form molecular solids , these molecules are then arranged in a specific pattern and held together by relatively weak intermolecular forces.

The individual water and sugar molecules each exist as their own independent entities that interact with their neighbors in specific ways to create an ordered crystalline solid. See Figure 5. In network solids , on the other hand, there are no individually defined molecules. A continuous network of covalent bonds holds together all the atoms. For example, carbon can form two different network solids: diamond and graphite. These materials are made up of only carbon atoms that are arranged in two different ways.

Diamond is a three-dimensional crystal that is the hardest known natural material in the world. In contrast, graphite is a two-dimensional network solid. The carbon atoms essentially form flat sheets, which are relatively slippery and can slide past each other.

While these two materials are made of the same very simple component — just carbon atoms — their appearance and behavior are completely different because of the different types of bonding in the solids.

See our Defining Minerals module for more about diamond and graphite. This ability of a single element to form multiple solids is called allotropy. Network solids can also incorporate multiple elements. The chemical formula for quartz is SiO 2 , but this formula indicates the ratio of silicon to oxygen and is not meant to imply that there are distinct SiO 2 molecules present. Each silicon atom is bonded to four different oxygen atoms and each oxygen atom is bonded to two different silicon atoms, creating a large network of covalent bonds , as shown in Figure 6.

Ionic solids are similar to network solids in one way: There are no distinct molecules. But instead of atoms held together by covalent bonds , ionic solids are composed of positively and negatively charged ions held together by ionic bonds. See our Chemical Bonding module for more about ionic bonding.

In the case of sodium chloride, sodium is the metal and chloride is the non-metal. Finally, metallic solids are a type all their own. Although we are discussing them last here, about three quarters of the known elements are metals.

You can read more about these metallic elements in The Periodic Table of Elements module. Here we will focus on how these elements behave as metallic solids. Metal atoms are held together by metallic bonds , in which the atoms pack together and the outer electrons can easily move around within the solid Figure 7. Metallic bonds are nondirectional , meaning that metal atoms can remain bonded while they roll against each other as long as some parts of their surfaces are in contact. These unique properties of metallic bonds are largely responsible for some of the valuable behavior of metals, including their conductivity and malleability , which we discuss in the next section.

As described in the previous section, crystalline solids can vary in their atomic compositions, bonding , and structure. Together, these attributes determine how the different solids behave under different conditions. Solids have many different properties, including conductivity , malleability , density , hardness, and optical transmission, to name a few.

We will discuss just a handful of these properties to illustrate some of the ways that atomic and molecular structure drives function. Those wires are made of metal, probably copper, because metals generally have good electrical conductivity. Electricity is essentially a flow of electrons from one place to another, and in metallic bonds the outer electrons are relatively free to move between adjacent atoms.

This electron mobility means it is easy for an electrical current to move from one end of a piece of metal to the other. When an electron is introduced at one end of a piece of wire by an electric current, this causes electrons to move from one to another metal atom continuously down the wire, allowing the current to flow.

In other solids , though, the electrons are engaged in the covalent or ionic bonds and therefore are not able to conduct electricity, or do so only poorly. Materials that do not conduct electricity are called electrical insulators. Heat, or thermal , conductivity is closely related to electrical conductivity. To understand how this works, consider that temperature is a measurement of how much molecules are moving see our States of Matter and Temperature modules. For a solid to conduct heat, the movement of one molecule or atom needs to be easily transferrable to its neighbor.

The non-directional nature of the metallic bond makes this type of transfer relatively easy, so metals conduct heat well. In a network solid, on the other hand, where the bonds are more rigid and the angles between the atoms are strictly defined, such transfer is more difficult.

Such solids would be expected to have low heat conductivity and would be called heat insulators. Graphite is an interesting exception to this trend. Because of the specific energy and orientation of the typical bonds in graphite sheets, they are relatively good at conducting heat and electricity. You may have heard about carbon nanotubes, which are similar to graphite sheets but exist in the form of tubes Figure 8. These tubes can conduct electricity and heat from one end to the other and are being tested for many possible applications, including in electrical circuits, solar cells, and textiles.

Two additional properties, malleability and ductility , follow trends similar to those for electrical and thermal conductivity. Malleability describes the ability to hammer a solid into a sheet without breaking it, and ductility refers to whether a solid can be stretched to form a wire. As you may have guessed, metals tend to be both malleable and ductile , largely due to the non-directionality of metallic bonds.

In contrast, covalent and ionic bonds , which are directional and require specific geometries resulting in fixed three-dimensional lattice structures, make many other types of solids brittle so they break under force.

Metallic malleability and ductility are a crucial reason that metals are so useful. They also create some drawbacks though. Manufacturers must consider all the properties of the materials they plan to work with to find the best option for each application. Another way to deform a solid is to melt it. For molecular solids , melting means breaking the weak intermolecular forces the forces between different molecules , not the strong covalent bonds that hold the individual molecules together, so a compound like sugar can be easily melted on your stovetop.

For network solids held together by covalent bonds , ionic solids held together by ionic bonds , and metallic solids held together by metallic bonds , though, the melting temperature depends on the strength of the specific bonds in each solid.

Ionic bonds tend to be weaker than covalent and metallic bonds , which is why the melting points for these salts are somewhat lower than most of the other example melting points included here.

Another approach is dissolving the solid into some type of liquid , in this case referred to as a solvent. The extent to which a solid dissolves in a particular solvent is called its solubility. Solids can be dissolved into a variety of types of solvents, but for now we will focus on solubility in water.

difference between crystalline and amorphous solids pdf

Crystalline solids have regular ordered arrays of components held together by uniform intermolecular forces, whereas the components of amorphous solids are not arranged in regular arrays. The learning objective of this module is to know the characteristic properties of crystalline and amorphous solids. With few exceptions, the particles that compose a solid material, whether ionic, molecular, covalent, or metallic, are held in place by strong attractive forces between them. When we discuss solids, therefore, we consider the positions of the atoms, molecules, or ions, which are essentially fixed in space, rather than their motions which are more important in liquids and gases. The faces of crystals can intersect at right angles, as in galena PbS and pyrite FeS 2 , or at other angles, as in quartz. Right Cleavage surfaces of an amorphous solid. Obsidian, a volcanic glass with the same chemical composition as granite typically KAlSi 3 O 8 , tends to have curved, irregular surfaces when cleaved.

Properties of Solids

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These pranks work well because salt and sugar are almost indistinguishable by the naked eye: Both are crystalline solids with similar structures.

12.1: Crystalline and Amorphous Solids

Polymer Morphology. They have characteristic geometrical shape 2. It provides guidance for solubility and dissolution testing of amorphous dispersions. Main Difference.

Mechanical Properties and Testing of Polymers pp Cite as. Amorphous is used as a description of the structure of a material and it implies that there is no long-range order such as that found in crystalline or liquid crystalline substances. Such disordered arrangements are found in melts.

Register Now. Hey there! We receieved your request. Difference between Crystalline and Amorphous Solids. On the basis of the arrangement of constituent particles, the solids are classified into two categories, namely:.


The major difference between crystalline and amorphous is crystalline solid is In crystalline solids the particles are arranged in a 3 dimensional order.


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