Chemistry
Molecular Solid
A molecular solid is a type of solid material in which the constituent particles are individual molecules held together by intermolecular forces. These solids have relatively low melting points and are typically soft and easily deformable. Examples of molecular solids include ice, sugar, and organic compounds such as paraffin wax.
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12 Key excerpts on "Molecular Solid"
eBook - PDFChemistry
Structure and Dynamics
- James N. Spencer, George M. Bodner, Lyman H. Rickard(Authors)
- 2011(Publication Date)
- Wiley(Publisher)
and bronze), or intermolecular compounds (such as Li 3 As) are metallic bonds. Distinguishing among solids that are primarily held together by covalent, ionic, or metal bonds is useful because it allows us to predict many of the physical prop- erties of the solid. 9.2 Molecular and Network Covalent Solids Molecular SolidS The iodine (I 2 ) that dissolves in alcohol to make the antiseptic known as tinc- ture of iodine, the cane sugar (C 12 H 22 O 11 ) found in a sugar bowl, and the poly- ethylene used to make garbage bags all have one thing in common. They are all examples of compounds that are Molecular Solids at room temperature. Water and bromine are liquids that form Molecular Solids when cooled slightly; H 2 O freezes at 0°C and Br 2 freezes at 7°C. Many substances that are gases at room temperature will form Molecular Solids when cooled far enough; F 2 , at the extreme right of the bond-type triangle in Figure 9.1, freezes to form a molecu- lar solid at 220°C. Molecular Solids contain both intramolecular bonds and intermolecular forces, as described in Chapter 8. The atoms within the individual molecules are held together by relatively strong intramolecular covalent bonds. Molecular Solids are therefore found in the covalent region of a bond-type triangle. The molecules in these solids are held together by much weaker intermolecular forces. Because intermolecular forces are relatively weak, Molecular Solids are often soft sub- stances with low melting points. Dry ice, or solid carbon dioxide, is a perfect example of a Molecular Solid. The van der Waals forces holding the CO 2 molecules together are weak enough that at dry ice sublimes at a temperature of 78ºC––it goes directly from the solid to the gas phase. Changes in the strength of the van der Waals forces that hold Molecular Solids together can have important consequences for the properties of the solid.
eBook - PDF- Young, William Vining, Roberta Day, Beatrice Botch(Authors)
- 2017(Publication Date)
- Cengage Learning EMEA(Publisher)
In an amorphous solid , the particles that make up the solid are arranged in an irregular manner and the solid lacks long-range order. Many important solid materials, such as synthetic fibers, plastics, and glasses, are amorphous, but pure solid substances, such as elemental phosphorus or sulfur, may also exist in amorphous forms. Because the lack of a well-defined repeating structure means that amorphous materi-als are more difficult to describe systematically, we restrict our discussion here to crystal-line solids. Like liquids, solids are condensed phases in which the constituent particles are in contact and the properties are determined by the nature of the interactions holding the particles together. Solids can be broadly classified, based on these interactions, as molecu-lar, ionic, covalent, or metallic (Interactive Table 13.1.1). Molecular Solids (also called van der Waals solids ) consist of individual molecules held together by relatively weak intermolecular forces (IMFs), such as dipole–dipole IMFs, hydrogen bonds, dipole–induced dipole IMFs, and London dispersion forces. The strengths of the IMFs holding the molecules near one another in the solid ( 0.05 to 30 kJ/mol) are much weaker than the strengths of the intramolecular covalent bonds ( 200 to 600 kJ/mol) between atoms within the molecules that make up the solid. The weak, non ionic IMFs between the molecules result in Molecular Solids that are generally low melting, do not conduct electricity, and have low hardness (resistance to deformation). Ionic solids are composed of oppositely charged ions combined to produce a neutral solid. The forces holding the ions together are the coulombic forces between the oppositely charged ions.
eBook - PDF- George C. King(Author)
- 2023(Publication Date)
- Wiley(Publisher)
8 Solids In Chapter 2, we discussed why a substance occurs in gaseous, liquid, or solid form. We saw that it was due to a competition between the binding energy of the constituent molecules and their thermal, kinetic energy. In gases, the kinetic energy dominates and the molecules are essentially free to move around their container, unaffected by their neighbours except for elastic collisions. Solids lie at the other extreme. In solids, the binding energy dominates and the molecules or atoms are tightly bound and closely packed together rigid. This results in the most characteristic property of solids. They have appreciable stiffness and maintain their shape. Solids appear in a wide variety of forms. Of these, crystalline solids provide an ideal form to understand the structure and properties of solids. This is because of their high degree of regularity; a reoccurring pattern of atomic positions that extends over many atoms. Consequently, we will focus most of our attention on the crystalline state of matter. Nearly everything we know about crystal structures has been learnt from dif- fraction experiments. In this chapter, we introduce the principles of X-ray crystallography and how it is used to determine crystal structure. We also relate the properties of solids to the forces acting between their constituent atoms. This follows on from our discussion of interatomic forces in Chapter 2. 8.1 Types of solids Solids may be classified as crystalline, amorphous, or polymeric. We may distinguish between crystalline and amorphous solids as follows. At sufficiently low temperatures, most substances will condense to form a solid. If the substance is cooled sufficiently slowly, the atoms have time to arrange themselves into a reg- ular array with long-range order. By this, we mean that there is a well-defined spatial relationship between atoms that are far from each other, i.e. much further than the mean distance between the atoms.
eBook - ePub- Jeffrey Gaffney, Nancy Marley(Authors)
- 2017(Publication Date)
- Elsevier(Publisher)
Most Molecular Solids are soft, but can also be ductile or brittle. While brittle solids fracture immediately when enough stress is applied, ductile solids undergo a period of deformation followed by fracture. The intermolecular forces in many Molecular Solids are directional, leading to mechanical properties that vary with the direction of the applied stress. Molecular Solids are usually insulators because the localization of electrons in the covalent bonds of the molecules prevents their movement in the crystal lattice. However, if an alkali metal is intercolated into the crystal lattice voids, the valence electrons on the alkali metal can be easily ionized allowing them to move freely in the crystal lattice. This gives the Molecular Solid electrical conductivity it would not otherwise have without significantly changing the other properties.11.4 Atomic Solids
Atomic solids , also called network solids, are composed of atoms connected by covalent bonds in a continuous network. There are two types of atomic solids: those that are totally composed of an extended three-dimensional covalent network and those that are composed of two-dimensional covalent networks, which are held together by weaker van der Waals forces (mixed bonding). In the three-dimensional networks, the covalent bonding extends throughout the solid and the result is a macroscopic interlocking covalent lattice structure. Any distortion of the crystal geometry can only occur through breaking the strong covalent bonds. In the two-dimensional networks, distortion of the three-dimensional geometry is more easily accomplished by disturbing the weaker intermolecular forces holding the two-dimensional planes together.The most common examples of atomic solids are the allotropes of carbon. These allotropes, different solid forms of carbon, are shown in Fig. 11.9
eBook - PDF- William Moebs, Samuel J. Ling, Jeff Sanny(Authors)
- 2016(Publication Date)
- Openstax(Publisher)
But the crystalline structures of semiconductors such as silicon have also made possible the electronics industry of today. In this chapter, we study how the structures of solids give them properties from strength and transparency to electrical conductivity. Chapter 9 | Condensed Matter Physics 401 9.1 | Types of Molecular Bonds Learning Objectives By the end of this section, you will be able to: • Distinguish between the different types of molecular bonds • Determine the dissociation energy of a molecule using the concepts ionization energy, electron affinity, and Coulomb force • Describe covalent bonding in terms of exchange symmetry • Explain the physical structure of a molecule in terms of the concept of hybridization Quantum mechanics has been extraordinarily successful at explaining the structure and bonding in molecules, and is therefore the foundation for all of chemistry. Quantum chemistry, as it is sometimes called, explains such basic questions as why H 2 O molecules exist, why the bonding angle between hydrogen atoms in this molecule is precisely 104.5° , and why these molecules bind together to form liquid water at room temperature. Applying quantum mechanics to molecules can be very difficult mathematically, so our discussion will be qualitative only. As we study molecules and then solids, we will use many different scientific models. In some cases, we look at a molecule or crystal as a set of point nuclei with electrons whizzing around the outside in well-defined trajectories, as in the Bohr model. In other cases, we employ our full knowledge of quantum mechanics to study these systems using wave functions and the concept of electron spin. It is important to remember that we study modern physics with models, and that different models are useful for different purposes. We do not always use the most powerful model, when a less-powerful, easier-to- use model will do the job. Types of Bonds Chemical units form by many different kinds of chemical bonds.
eBook - PDFThermodynamics and Statistical Mechanics
An Integrated Approach
- M. Scott Shell(Author)
- 2015(Publication Date)
- Cambridge University Press(Publisher)
14 Solids 14.1 General properties of solids The term “solids” denotes materials that generally have the following properties. From a microscopic perspective, the molecules in a solid are in a condensed, closely packed state, and they vibrate around a fixed equilibrium position. That is, molecules can be considered tethered near a specific location in space, since their diffusion is very slow relative to the time scales of observation. From a macroscopic point of view, solids have an elastic modulus. This means that the application of a stress to the material produces a strain as well as an opposing force that tends to return the solid to its original, unstrained state once the stress is removed. This contrasts with viscous behavior in which an applied stress results in continuous, permanent deformation, such as the flow of a liquid. Generally speaking, there are two primary classes of solids. Crystalline solids are equilibrium states of matter in which the microscopic structure has a well-defined geometric pattern with long-range order: a crystalline lattice. In contrast to crystals, amorphous solids have no long-range order, meaning that they lack a lattice structure and regular positioning of the molecules. Glasses and many polymeric materials are amorphous. Frequently these systems are not at equilibrium, but evolve very slowly in time and are metastable with respect to a crystalline phase. They might be considered liquids of extremely high viscosity that are slowly en route to crystallization. However, typically the time scale to reach equilibrium is so long (perhaps longer than the age of the universe) that for all practical purposes the amorphous state appears solid and stable. Thus, in an empirical sense, often we can treat such systems as in quasi- equilibrium.
eBook - PDF- Edward J. Neth, Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson(Authors)
- 2019(Publication Date)
- Openstax(Publisher)
In this chapter, the nature of these interactions and their effects on various physical properties of liquid and solid phases will be examined. Figure 10.1 Solid carbon dioxide (“dry ice”, left) sublimes vigorously when placed in a liquid (right), cooling the liquid and generating a dense mist of water above the cylinder. (credit: modification of work by Paul Flowers) CHAPTER OUTLINE 10.1 Intermolecular Forces LEARNING OBJECTIVES By the end of this section, you will be able to: • Describe the types of intermolecular forces possible between atoms or molecules in condensed phases (dispersion forces, dipole-dipole attractions, and hydrogen bonding) • Identify the types of intermolecular forces experienced by specific molecules based on their structures • Explain the relation between the intermolecular forces present within a substance and the temperatures associated with changes in its physical state As was the case for gaseous substances, the kinetic molecular theory may be used to explain the behavior of solids and liquids. In the following description, the term particle will be used to refer to an atom, molecule, or ion. Note that we will use the popular phrase “intermolecular attraction” to refer to attractive forces between the particles of a substance, regardless of whether these particles are molecules, atoms, or ions. Consider these two aspects of the molecular-level environments in solid, liquid, and gaseous matter: • Particles in a solid are tightly packed together and often arranged in a regular pattern; in a liquid, they are close together with no regular arrangement; in a gas, they are far apart with no regular arrangement. • Particles in a solid vibrate about fixed positions and do not generally move in relation to one another; in a liquid, they move past each other but remain in essentially constant contact; in a gas, they move independently of one another except when they collide.
eBook - PDFChemistry
An Atoms First Approach
- Steven Zumdahl, Susan Zumdahl, Donald J. DeCoste, , Steven Zumdahl, Steven Zumdahl, Susan Zumdahl, Donald J. DeCoste(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
These substances all have atoms at the lattice points that describe the structure of the solid. Therefore, we call solids of this type atomic solids. Examples of these three types of solids are shown in Fig. 9.27. To summarize, we find it convenient to classify solids according to what type of component occupies the lattice points. This leads to the classifications atomic solids (atoms at the lattice points), Molecular Solids (discrete, relatively small molecules at the lattice points), and ionic solids (ions at the lattice points). In addition, atomic solids are placed into the following subgroups based on the bonding that exists among the atoms in the solid: metallic solids, network solids, and Group 8A (18) solids. In metal- lic solids, a special type of delocalized nondirectional covalent bonding occurs. In network solids, the atoms bond to each other with strong directional covalent bonds that lead to giant molecules, or networks, of atoms. In the Group 8A (18) solids, the noble gas elements are attracted to each other with London dispersion forces. The clas- sification of solids is summarized in Table 9.7. The markedly different bonding present in the various atomic solids leads to dra- matically different properties for the resulting solids. For example, although argon, copper, and diamond all are atomic solids, they have strikingly different properties. Buckminsterfullerene, C 60 , is a particular member of the fullerene family. The internal forces in a solid determine the properties of the solid. 387 9.5 An Introduction to Structures and Types of Solids Copyright 2021 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience.
eBook - PDF- William R. Robinson, Edward J. Neth, Paul Flowers, Klaus Theopold, Richard Langley(Authors)
- 2016(Publication Date)
- Openstax(Publisher)
In the following description, the term particle will be used to refer to an atom, molecule, or ion. Note that we will use the popular phrase “intermolecular attraction” to refer to attractive forces between the particles of a substance, regardless of whether these particles are molecules, atoms, or ions. Consider these two aspects of the molecular-level environments in solid, liquid, and gaseous matter: • Particles in a solid are tightly packed together and often arranged in a regular pattern; in a liquid, they are close together with no regular arrangement; in a gas, they are far apart with no regular arrangement. • Particles in a solid vibrate about fixed positions and do not generally move in relation to one another; in a liquid, they move past each other but remain in essentially constant contact; in a gas, they move independently of one another except when they collide. The differences in the properties of a solid, liquid, or gas reflect the strengths of the attractive forces between the atoms, molecules, or ions that make up each phase. The phase in which a substance exists depends on the relative extents of its intermolecular forces (IMFs) and the kinetic energies (KE) of its molecules. IMFs are the various forces of attraction that may exist between the atoms and molecules of a substance due to electrostatic phenomena, as will be detailed in this module. These forces serve to hold particles close together, whereas the particles’ KE provides the energy required to overcome the attractive forces and thus increase the distance between particles. Figure 10.2 illustrates how changes in physical state may be induced by changing the temperature, hence, the average KE, of a given substance. Figure 10.2 Transitions between solid, liquid, and gaseous states of a substance occur when conditions of temperature or pressure favor the associated changes in intermolecular forces.
eBook - PDFChemistry
The Molecular Nature of Matter
- Neil D. Jespersen, Alison Hyslop(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
578 CHAPTER 11 Intermolecular Attractions and the Properties of Liquids and Solids forces holding the solid together. Even though we can’t make exact predictions about such properties, some generalizations do exist. In discussing them, it is convenient to divide crystals into four types: ionic, molecular, covalent, and metallic. Ionic Crystals Ionic crystals have ions at the lattice sites and the binding between them is mainly electro- static, which is essentially nondirectional. As a result, the kind of lattice formed is determined mostly by the relative sizes of the ions and their charges. When the crystal forms, the ions arrange themselves to maximize attractions and minimize repulsions. Because electrostatic forces are strong, ionic crystals tend to be hard. They also tend to have high melting points because the ions have to be given a lot of kinetic energy to enable them to break free of the lattice and enter the liquid state. The forces between ions can also be used to explain the brittle nature of many ionic compounds. For example, when struck by a hammer, a salt crystal shatters into many small pieces. A view at the atomic level reveals how this could occur (Figure 11.51). The slight movement of a layer of ions within an ionic crystal suddenly places ions of the same charge next to each another, and for that instant there are large repulsive forces that split the solid. In the solid state, ionic compounds do not conduct electricity because the charges pres- ent are not able to move. However, when melted, ionic compounds are good conductors of electricity. Melting frees the electrically charged ions to move. Molecular Crystals Molecular crystals are solids in which the lattice sites are occupied either by atoms (as in solid argon or krypton) or by molecules (as in solid sulfur, (S 8 ), PF 5 , SO 2 , or H 2 O).
eBook - PDF- Peter Hedvig(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
8.1 STRUCTURE AND MOLECULAR MOBILITIES OF ORGANIC SOLIDS The chemical properties of organic solids are basically determined by their physical structure. On the other hand the physical structure of the solid is connected with the structure of the molecules of which it is com-posed. It has been shown in Chapter 6 that the symmetry of a molecule is determined by the symmetry of the atomic orbitals. The tetragonal sym-metry of methane for example is a direct consequence of the tetragonal symmetry of the sp* hybrid orbital of the carbon atom. Similarly the sym-metry properties of crystals are determined by the symmetries of the mo-lecular orbitals. From this point of view all organic solids are expected to be crystalline. Crystallinity of a solid means translational symmetry. In a crystalline solid it is possible to find such groups of molecules which can be made coin-cide by simple translation. Such a group is referred to as the unit cell of the crystal: the molecular configuration of the unit cell is repeated over all the crystal. The unit cell may contain several atoms or molecules arranged to result in a structure of definite symmetry. In a perfect crystal all lattice sites are occupied with atoms or molecules and no other molecules are pres-ent. In a real crystal some lattice sites may be missing, some atoms or molecules may be dislocated from their correct place (dislocations) and some foreign impurity molecules may be present. These irregularities of the crystal lattice are called lattice defects. It has been found that even in the most carefully grown perfect looking crystals quite a high defect con-centration is present [8.2]. The translational symmetry of a crystal is usually three dimensional. There are, however, such organic crystals which exhibit only two dimension-al translational symmetry, i.e. the unit cell is only repeated in a plane, the third dimension is not ordered. These are referred to as liquid crystals or smectic phases.
eBook - PDF- Lesley E Smart, J M F Gagan(Authors)
- 2007(Publication Date)
- Royal Society of Chemistry(Publisher)
Part I Crystals L Y You will be aware how atoms sometimes bond together to make individual molecules, as in carbon dioxide, chlorine and iodine for instance, but how in other cases, like diamond, silica, and sodium chloride, it is not possible to distinguish individual molecules (Figures 1. la-d). You should also remember that bonding, and thus the arrangement of electrons, influences the shape of a molecule such as ammonia (Figure 1. le). Many chemicals are solids at normal temperatures, and in the first part of this Book we are going to investigate the variety of structures adopted by elements and compounds in the crystalline solid state. The second part of the Book will concentrate only on the structure and shape of individual molecules. Figure 1.1 (a) Uncut and cut diamonds; (b) a sample of chlorine; (c) the structure of diamond; (d) the structure of the chlorine molecule; (e) the distribution of outer electrons i n the ammonia molecule dictates its pyramidal shape. 1 * * This symbol, 8, indicates that this Figure is available in WebLab ViewerLiteTM on one of the CD-ROMs associated with this Book. To begin with, we are going to look at the structure of metals and of ionic solids. Such materials are very different from those containing individual molecules, in that they comprise extended arrays of atoms or ions in which discrete molecules are not identifiable. For instance, as well as diamond (Figure 1 . lc) we can consider another familiar example, sodium chloride (common salt, Figure 1.2a), which has the empir- ical formula NaC1. Although the formula gives us the highly important information that there is one sodium atom present for every chlorine atom, it disguises the fact that crystalline sodium chloride does not comprise discrete NaCl molecules.
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