Atoms of a Solid Line Up in a Repeats Over and Over Again
12.1: Crystalline and Baggy Solids
- Folio ID
- 6402
Learning Objectives
- To empathize the difference between a crystalline and an baggy solid
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.
Introduction
With few exceptions, the particles that compose a solid material, whether ionic, molecular, covalent, or metallic, are held in place by strong bonny forces between them. When we discuss solids, therefore, nosotros 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 constituents of a solid can exist bundled in ii general ways: they can form a regular repeating iii-dimensional structure called a crystal lattice, thus producing a crystalline solid, or they can aggregate with no item order, in which case they form an baggy solid (from the Greek ámorphos, meaning "shapeless").
(left) Crystalline faces. The faces of crystals can intersect at correct angles, every bit in galena (PbS) and pyrite (FeS2), or at other angles, every bit in quartz.(Correct) Cleavage surfaces of an amorphous solid. Obsidian, a volcanic glass with the same chemic composition as granite (typically KAlSithreeO8), tends to have curved, irregular surfaces when cleaved.
Crystalline solids, or crystals, have distinctive internal structures that in plough lead to distinctive flat surfaces, or faces. The faces intersect at angles that are characteristic of the substance. When exposed to x-rays, each structure likewise produces a distinctive blueprint that can be used to place the material. The characteristic angles do not depend on the size of the crystal; they reverberate the regular repeating system of the component atoms, molecules, or ions in space. When an ionic crystal is cleaved (Effigy 12.1), for example, repulsive interactions cause it to interruption along fixed planes to produce new faces that intersect at the same angles as those in the original crystal. In a covalent solid such as a cut diamond, the angles at which the faces meet are also non arbitrary but are determined by the arrangement of the carbon atoms in the crystal.
Figure 12.ane: Cleaving a Crystal of an Ionic Compound along a Plane of Ions. Deformation of the ionic crystal causes one plane of atoms to slide along another. The resulting repulsive interactions between ions with like charges crusade the layers to separate.
Crystals tend to accept relatively abrupt, well-defined melting points because all the component atoms, molecules, or ions are the same distance from the same number and type of neighbors; that is, the regularity of the crystalline lattice creates local environments that are the same. Thus the intermolecular forces property the solid together are compatible, and the same corporeality of thermal energy is needed to suspension every interaction simultaneously.
Amorphous solids have two characteristic backdrop. When cleaved or broken, they produce fragments with irregular, often curved surfaces; and they have poorly defined patterns when exposed to x-rays because their components are not arranged in a regular array. An amorphous, translucent solid is called a glass. Almost whatever substance tin can solidify in amorphous grade if the liquid phase is cooled apace enough. Some solids, however, are intrinsically baggy, because either their components cannot fit together well enough to form a stable crystalline lattice or they contain impurities that disrupt the lattice. For instance, although the chemical composition and the basic structural units of a quartz crystal and quartz glass are the same—both are SiO2 and both consist of linked SiO4 tetrahedra—the arrangements of the atoms in space are not. Crystalline quartz contains a highly ordered arrangement of silicon and oxygen atoms, but in quartz glass the atoms are arranged almost randomly. When molten SiO2 is cooled rapidly (iv Thousand/min), it forms quartz drinking glass, whereas the large, perfect quartz crystals sold in mineral shops accept had cooling times of thousands of years. In contrast, aluminum crystallizes much more speedily. Amorphous aluminum forms but when the liquid is cooled at the extraordinary rate of 4 × 1013 Chiliad/south, which prevents the atoms from arranging themselves into a regular array.
The lattice of crystalline quartz (SiO2). The atoms class a regular organization in a structure that consists of linked tetrahedra.
In an amorphous solid, the local surround, including both the distances to neighboring units and the numbers of neighbors, varies throughout the material. Different amounts of thermal energy are needed to overcome these different interactions. Consequently, baggy solids tend to soften slowly over a wide temperature range rather than having a well-defined melting betoken like a crystalline solid. If an amorphous solid is maintained at a temperature just below its melting point for long periods of time, the component molecules, atoms, or ions can gradually rearrange into a more highly ordered crystalline form.
| Note |
|---|
| Crystals have abrupt, well-defined melting points; amorphous solids do not. |
Summary
Solids are characterized by an extended iii-dimensional system of atoms, ions, or molecules in which the components are generally locked into their positions. The components tin exist arranged in a regular repeating three-dimensional array (a crystal lattice), which results in a crystalline solid, or more or less randomly to produce an baggy solid. Crystalline solids have well-defined edges and faces, diffract x-rays, and tend to have abrupt melting points. In contrast, amorphous solids have irregular or curved surfaces, do non requite well-resolved x-ray diffraction patterns, and cook over a wide range of temperatures.
Conceptual Bug
1. Compare the solid and liquid states in terms of
a. rigidity of structure.
b. long-range order.
c. short-range order.
two. How do amorphous solids differ from crystalline solids in each characteristic? Which of the two types of solid is well-nigh similar to a liquid?
a. rigidity of structure
b. long-range order
c. short-range club
iii. Why is the arrangement of the elective atoms or molecules more of import in determining the backdrop of a solid than a liquid or a gas?
iv. Why are the structures of solids ordinarily described in terms of the positions of the constituent atoms rather than their motion?
5. What concrete characteristics distinguish a crystalline solid from an amorphous solid? Describe at least two ways to determine experimentally whether a material is crystalline or amorphous.
6. Explicate why each characteristic would or would non favor the germination of an baggy solid.
a. slow cooling of pure molten textile
b. impurities in the liquid from which the solid is formed
c. weak intermolecular bonny forces
7. A student obtained a solid product in a laboratory synthesis. To verify the identity of the solid, she measured its melting point and constitute that the material melted over a 12°C range. After it had cooled, she measured the melting point of the aforementioned sample once more and constitute that this time the solid had a sharp melting point at the temperature that is characteristic of the desired production. Why were the 2 melting points unlike? What was responsible for the alter in the melting point?
Conceptual Answers
3. The organisation of the atoms or molecules is more important in determining the backdrop of a solid because of the greater persistent long-range order of solids. Gases and liquids cannot readily be described by the spatial arrangement of their components because rapid molecular motion and rearrangement defines many of the backdrop of liquids and gases.
vii. The initial solid contained the desired compound in an amorphous land, every bit indicated by the wide temperature range over which melting occurred. Wearisome cooling of the liquid caused it to crystallize, as evidenced by the sharp 2d melting point observed at the expected temperature.
Source: https://chem.libretexts.org/Bookshelves/General_Chemistry/Book:_General_Chemistry:_Principles_Patterns_and_Applications_%28Averill%29/12:_Solids/12.01:_Crystalline_and_Amorphous_Solids
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