DOCSLIB.ORG

Chemical Bonding in Solids Download Free

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Chemical Bonding in Solids Download Free CHEMICAL BONDING IN SOLIDS Author: Jeremy K. Burdett Number of Pages: 336 pages Published Date: 30 Mar 1995 Publisher: Oxford University Press Inc Publication Country: New York, United States Language: English ISBN: 9780195089929 DOWNLOAD: CHEMICAL BONDING IN SOLIDS Chemical Bonding in Solids PDF Book Eisenberg and W. Metallic solids have unusual properties: in addition to having high thermal and electrical conductivity and being malleable and ductile, they exhibit luster, a shiny surface that reflects light. Classify Ge, RbI, C 6 CH 3 6 , and Zn as ionic, molecular, covalent, or metallic solids and arrange them in order of increasing melting points. Electronic properties of some inorganic solids. In the late 's synthetic methods were developed for the synthesis of C 60 , and the ready availability of this form of carbon led to extensive research into its properties. Hydrogen bonding is a term describing an attractive interaction between a hydrogen atom from a molecule or a molecular fragment X—H in which X is more electronegative than H, and an atom or a group of atoms in the same or a different molecule, in which there is evidence of bond formation. The atoms within such a metallic solid are held together by a unique force known as metallic bonding that gives rise to many useful and varied bulk properties. Molecules 1. Toluene and m-xylene. The substances used are innocuous and do not require special handling. A piece of paper can be passed between the magnet and the paper clip to show that there is no direct, physical connection between the two. The material can stretch, but when snapped into pieces it can bond back together again through reestablishment of its hydrogen-bonding network without showing any sign of weakness. Covalent Network Solids Covalent solids are formed by networks or chains of atoms or molecules held together by covalent bonds. These molecules are held to one another by hydrogen bonds if they can form them , dispersion forces, and other dipolar forces—in that order of decreasing importance—and the molecules stack together in a pattern that minimizes their total energy. Molecular solids A solid that consists of molecules held together by relatively weak forces, such as dipole-dipole interactions, hydrogen bonds, and London dispersion forces. Although simple models of bonding are useful as rules of thumb for rationalizing the existence of compounds and the physical and chemical properties and structures of molecules, they need to be justified by appealing to more-sophisticated descriptions of bonding. A classic molecular solid consists of small, non-polar covalent molecules, and is held together by London dispersion forces van der Waals forces ; a classic example is paraffin wax. The Hume-Rothery Rules 8. Also of Interest. Given: compounds. The H2 Molecule: Localized Approach 1. Energy Levels of Cyclic Polyenes 1. What is the hybridization of carbon in diamond? Chemical Bonding in Solids Writer The full theory of the structure of metals is a highly technical subject as are the full theories of the other topics discussed here. Chemical Bonding in Ionic Compounds 4. Lewis suggested that the union of atoms by bonding in molecules like hydrogen , nitrogen, oxygen, chlorine, etc, and most of the organic chemical compounds like hydrocarbon , alcohols , organic acids, etc. In each bonding, the chemical atom attains its stable inert gas configuration. The basic ideas are illustrated in the lab involving chemical bonding in solids found on page 4. Classify Ge, RbI, C 6 CH 3 6 , and Zn as ionic, molecular, covalent, or metallic solids and arrange them in order of increasing melting points. Remove the conductivity tester from the first beaker and rinse its contacts wires with distilled water. Journal of the American Chemical Society. Magnetic Analogy for Bonding Forces … see page 2 c. One of the goals of this text is to bring some of these ideas together and show how a broader picture exists once some of the prejudices which isolate one area from another are removed. The name is a tribute to the American architect R. The variation in the relative strengths of these four types of interactions correlates nicely with their wide variation in properties. The strength of metallic bonds varies dramatically. Comparing the mechanical properties of an alloy with those of the parent metal could be used to decide whether the alloy were a substitutional or interstitial alloy. Clean the electrodes and then test solid sucrose light bulb remains dark. The packing efficiency in metallic crystals tends to be high, so the resulting metallic solids are dense, with each atom having as many as 12 nearest neighbors. How many valence electrons does a sodium, silicon, beryllium, and oxygen atom have? Bonding in metallic solids is quite different from the bonding in the other kinds of solids we have discussed. The metallic atoms will reorganize and squeeze through whereas the ionic crystal will resist going through intact. The unit cell of diamond can be described as an fcc array of carbon atoms with four additional carbon atoms inserted into four of the tetrahedral holes. Friend Reviews. Every halogen atom has seven electrons in its outermost orbital. Although most of the chemical properties of the metal can explain by metallic bonding but the heat capacity of metals difficult to explain by the electron sea model definition. Briefly describe the bonding in metals that explains such properties. Magnetic Analogy for Bonding Forces. It was easily realized that the number of atoms or groups of atoms combines to form the ions or molecules. See Figure The Structure of NbO 4. Questions to consider What is the bonding geometry around each carbon? It is difficult to deform or melt these and related compounds because strong covalent C—C or Si—Si or polar covalent Si—C or Si—O bonds must be broken, which requires a large input of energy. The electrostatic forces bind together oppositely charged ions in chemical compounds responsible for the formation of ionic bonds. Solids can be classified according to the nature of the bonding between their atomic or molecular components. In any case, students should point out that polar covalent bonds, depending on molecular geometry, often give a molecule properties that affect its behavior. The structure of crystalline quartz SiO 2 , shown in Section What are valence electrons? The metallic chemical bonding may be the collection of positive atomic cores and mobile electrons in the electron sea model. Conceptual Problems Four vials labeled A—D contain sucrose, zinc, quartz, and sodium chloride, although not necessarily in that order. Metallic bonds tend to be weakest for elements that have nearly empty as in Cs or nearly full Hg valence subshells, and strongest for elements with approximately half-filled valence shells as in W. Chemical Bonding in Solids Reviews In addition, a single stick is drawn to represent a covalent bond irrespective of whether the bond is a single, double, or triple bond or requires resonance structures to represent. Determine the number of valence electrons in an atom from its position in the periodic table. Have the students assemble the ionic crystal lattice. When two pairs approach, new attractive forces arise between the "nucleus" of one pair and the "electron" of the other pair, and vice versa. For example, hydrogen has one valence electron; it's in the alkali metal family. Topological aspects of chemical bonding and structure explored through the method of moments. In network solids, conventional chemical bonds hold the chemical subunits together. Melting points are typically moderately high, but some combinations of molecular cations and anions yield an ionic liquid with a freezing point below room temperature. Because scientists can combine two or more metals in varying proportions to tailor the properties of a material for particular applications, most of the metallic substances we encounter are actually alloys. The Coloring Problem 8. Low Melting Point, Nonconducting. The electron donor forms a positively charged particle cation and the acceptor becomes negatively charged an anion. One is the attractive force between opposite charges of polar molecules. Britannica Quiz. What force holds the carbon sheets together in graphite? Activities: 1. A Germanium lies in the p block just under Si, along the diagonal line of semimetallic elements, which suggests that elemental Ge is likely to have the same structure as Si the diamond structure. The Importance of Structure and Composition 5. Covalent solids are formed by networks or chains of atoms or molecules held together by covalent bonds. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide. Although the elemental composition of most alloys can vary over wide ranges, certain metals combine in only fixed proportions to form intermetallic compounds with unique properties. Nonmetal atoms tend to gain electrons to acquire a noble gas electron configuration, giving them a net negative electric charge. Chemical Bonding in Solids Read Online Note the Pattern Valence electrons in a metallic solid are delocalized, providing a strong cohesive force that holds the atoms together. Materials: Styrofoam balls preferably different colors and sizes … blocks could be used as well , toothpicks and contact cement. Very little energy is needed to remove electrons from a solid metal because they are not bound to a single nucleus. Each orbital has a characteristic energy, and the range of energies spanned by the n orbitals is finite, however great the value of n. The a layer of the graphite structure consists of a repeating series of rings. The strength of the attractive forces depends on the charge and size of the ions that compose the lattice and determines many of the physical properties of the crystal. Although the elemental composition of most alloys can vary over wide ranges, certain metals combine in only fixed proportions to form intermetallic compounds with unique properties.
Load more

Recommended publications
  • Bonding in Solids, Structural and Chemical Properties - R
    MATERIALS SCIENCE AND ENGINEERING – Vol. I – Bonding in Solids, Structural and Chemical Properties - R. W. Grimes BONDING IN SOLIDS, STRUCTURAL AND CHEMICAL PROPERTIES R. W. Grimes Imperial College, London, UK Keywords: Atomic structure, band structure, bonding, bulk modulus, conductivity, covalent, defects, electrons, energy level, hydrogen bonding, hybridization, insulators, ionic, metal, molecule, orbital, quantum, Schrödinger equation, semi-conductors, wave function. Contents 1. Introduction 2. Atomic Orbitals: their Origin and their Shapes 2.1. The Four Quantum Numbers 2.2. The Schrödinger Equation 2.3. Atoms with more than One Electron 3. Forming Bonds between like Atoms: Bonding and Anti-bonding Molecular Orbitals, Sigma and Pi-bonds 3.1. The Born-Oppenheimer Approximation 3.2. The Molecular Orbital Approximation 3.3. Linear Combination of Atomic Orbitals + 3.4. The Binding Curve for H2 3.5. Predicting the Stability of Other Simple Molecules 3.6. The Fluorine Diatomic Molecule: Another Homonuclear Molecule 4. Forming Bonds between Unlike Atoms: Polar Covalent and Ionic Bonds, Two Extremes of the Same Process 4.1. HF, a Polar Covalent Molecule 4.2. NaF, an Ionic Molecule 5. A Simple Model for an Ionic Solid: A Balance between Coulombic Attraction and Short-range Repulsion 5.1. Effective Potentials for Ionic Molecules 5.2. Extending the Model to Bulk NaF 5.3. CalculatingUNESCO the Bulk Modulus – EOLSS 6. From Hybridization to Conjugation to Band Structures: Why Diamond and Graphite have such Different Properties 6.1. Carbon 6.2. HybridizationSAMPLE and Molecular Orbitals CHAPTERS 7. More about Bands: Metals, Insulators and Semiconductors 7.1. Forming Bands in Metals 7.2.
    [Show full text]
  • BONDING in SOLIDS Engineering Physics
    Vignan BONDING IN SOLIDS Engineering Physics 1.1 Types of Bonding:- Different charge distributions in the atoms give rise to different types of bonding. They classified into five classes 1. Ionic bonding 2. Covalent bonding 3. Metallic bonding 4. Hydrogen bonding 5. Vander-Waals bonding Based on the bond strength atomic bonding can be grouped into “primary” and “secondary” bonding. Primary bonding:- Primary bonding have energies in the range of 1-10 eV. Ionic, covalent and metallic bonds are examples of primary bonding among these ionic and covalent bondings are generally stronger than the metallic bonding. Secondary bonding:- Secondary bonding have energies in the range of 0.01- 0.5 eV/ bond Hydrogen bonding and Vander Waals bonding are examples of secondary bonding. Generally, Vander Waals bonding is the weakest of all. 1 Vignan BONDING IN SOLIDS Engineering Physics 1.2 Ionic bonding (or) Hetro-Polar bond:- 1. Ionic bond is also called as “Hetro-Polar bond”. 2. Crystals in which ionic bond is present are known as “ionic crystals”. Ionic crystals are mostly insulating in character. Ex:-Nacl, NaBr, KBr, Mgo etc... 3. An Ionic bonding can only be formed between two different atoms, one electropositive and other electronegative. 4. Electropositive elements readily give up electrons and are usually group Ι (or) ΙΙ Elements e.g. Na, k, Ba. 5. Whereas electronegative elements readily take up electrons and are usually Group VΙ (or) VΙΙ elements e.g. Cl, Br and O. An example of the ionic bonding is NaCl. When neutral atom of a Na and Cl are brought close together it is easy for the valence electron of the sodium atom to be transferred to the chlorine atom so that both of them acquire a stable inert gas electronic configuration.
    [Show full text]
  • Representation of the States of Matter
    Chapter 10 Liquids & Solids Return to Slide 3 Representation of the states of Sublimation matter. Dry ice (solid CO2). Photo courtesy of American Color. PV = nRT ? ? Changes of State Intermolecular Forces • A change of state or phase transition is a Forces between (rather than within) molecules. change of a substance from one state to another. º dipole-dipole attraction: molecules with dipoles orient themselves so that “+” and gas “−” ends of the dipoles are close to each boiling condensation other. sublimation liquid condensation or º hydrogen bonds: dipole-dipole attraction in (see Figure 11.3) deposition which hydrogen is bound to a highly melting freezing electronegative atom. (F, O, N) solid 1 Hydrogen Bonding • Hydrogen bonding is a force that exists between a hydrogen atom covalently bonded to a very electronegative atom, X, and a lone pair of electrons on a very electronegative atom, Y. • To exhibit hydrogen bonding, one of the following three structures must be present. : : : H NOHFH • Only N, O, and F are electronegative enough to leave the hydrogen nucleus exposed. Dipole-Dipole Forces • Polar molecules can attract one another Figure 11.23: through dipole-dipole forces. Fluoromethane • The dipole-dipole force is an attractive and methanol. intermolecular force resulting from the tendency of polar molecules to align themselves positive end to negative end. δ+ H Cl δ− δ+ H Cl δ− Figure 11.21 shows the alignment of polar molecules. Hydrogen Bonding Figure 10.2: • A hydrogen atom bonded to an electronegative (a) The electrostatic interaction of two atom appears to be special. polar molecules. • The electrons in the O-H bond are drawn to the O (b) The interaction atom, leaving the dense positive charge of the of many dipoles in a hydrogen nucleus exposed.
    [Show full text]
  • Introduction • Bonding in Solids • Ionic Bond • Covalent Bond • Metallic Bond • Intermolecular Forces
    Topic 1: Introduction. Families of materials and applications Universidad Carlos III de Madrid MATERIALSCIENCIA E INGENIERÍA SCIENCE AND DE ENGINEERING MATERIALES www.uc3m.es TOPIC 1.2. BONDING IN SOLIDS. RELATION BETWEEN BONDING, STRUCTURE AND PROPERTIES OF MATERIALS • Introduction • Bonding in solids • Ionic bond • Covalent bond • Metallic bond • Intermolecular forces Dpt. Materials Sci. and Eng. and Chem. Eng. UC3M Sophia A. Tsipas / Dania Olmos 1 Topic 1: Introduction. Families of materials and applications INTRODUCTION Nature of bonding <> properties <> type of materials <> Processing and applications Applications Processing Structure Properties Dpt. Materials Sci. and Eng. and Chem. Eng. UC3M Sophia A. Tsipas / Dania Olmos 2 Topic 1: Introduction. Families of materials and applications IONIC BOND It forms between a metal and a non metal. There is electron transfer from the less electronegative atom to the more electronegative . Bonding forces ⇒ F electrostatic attraction between opposite charged ions. • Pure ionic bond: ideal. • ⇒ Always exists covalent participation Dpt. Materials Sci. and Eng. and Chem. Eng. UC3M Sophia A. Tsipas / Dania Olmos 3 Topic 1: Introduction. Families of materials and applications IONIC BOND Ionic compounds are crystalline solids It is a non directional bond formed by strong electrostatic interactions LATTICE ENERGY: Energy released when a mole of ionic solid is formed from its ions in the gas state. Born-Haber cycle for LiF. Step ΔH(kJ/mol) Na+ Sublimation of Li 155.2 Cl- Dissociation of F2 (g) 150.6 Ionization of Li(g) 520 - Gain of e of F(g) -328 Formation of LiF from Li(s) and -594.1 ½F2(g) Dpt. Materials Sci.
    [Show full text]
  • 1 Chemical Bonding in Solids
    j1 1 Chemical Bonding in Solids In this chapter, we discuss different mechanisms that can lead to bonding between atoms so that they form solids. We will encounter different cases such as ionic, covalent, or metallic bonding. It has to be kept in mind that these are just idealized limiting cases. Often mixed bonding types are found, for example, a combination of metallic and covalent bonding in the transition metals. As in conventional chemistry, only a restricted number of all the electrons participate in the bonding. These so-called valence electrons are the electrons in the outermost shell(s) of an atom. The electrons in the inner shells, or core electrons, are bound so tightly to the nucleus that they do not feel the presence of other atoms in their neighborhood. 1.1 Attractive and Repulsive Forces Two different forces must be present to establish bonding in a solid or in a molecule. An attractive force is necessary for any bonding. Different types of attractive forces are discussed below. A repulsive force, on the other hand, is required in order to keep the atoms from getting too close to each other. An expression for an interatomic potential can be written as A B f(r) ¼ À ; ð1:1Þ rn rm where n > m, that is, the repulsive part has to prevail for short distances (sometimes this is achieved by assuming an exponential repulsion potential). Such a potential and the resulting force are shown in Figure 1.1. The reason for the strong repulsion at short distances is the Pauli exclusion principle.
    [Show full text]
  • Chapter 2 Bonding in Solids
    2‐1 Chapter 2 Bonding in Solids Crystalline materials exhibit the complete spectrum of bond types: ionic, covalent, van der Waals, metallic. * In salts of complex anions, e.g. Li2SO4 have both ionic and covalent bonds. * Commonly, bonds are a blend of different types, e.g. TiO is ionic/metallic; CdI2 is ionic/covalent/van der Waals * In discussing structures, it is convenient to ignore temporarily the complexities of mixed bond types and to treat bonds as though they were purely ionic. Ionic bonding− structure with high symmetry and coordination number as high as possible, such that the electrostatic attractive force is maximized. Alkali and alkaline earth elements usually form ionic structures (Be is an exception), especially in combination with small electronegative anions such as O2- and F-. Covalent bonding− highly directional bonds irrespective of other atoms that are present, and CN is usually small. Covalent structure occur with (a) small atoms with high valence which, in the cationic state, would 3+ 4+ 4+ 4+ be highly polarizing 具極化能力, e.g. B , Si , P , S , etc.; (b) large atoms which in the anionic state are highly polarizable 易被極化但不丟電子, e.g. I-, S2-. Most non-molecular materials have mixed ionic and covalent bonding: * Ionicity ≡ percentage of ionic character in the bond * Transition metal compounds: the occurrence of metallic bonding 2‐2 2.1 Ionic bonding Purely ionic bonding rarely occurs. Even NaCl and CaO have some partial covalent character. The degree of covalent bonding increases with valence and ions with a net charge greater than +1 or −1 are unlikely to exist.
    [Show full text]
  • Bonding in Solids Bonding in Solids • There Are Four Types of Solid: 1
    Bonding in Solids Bonding in Solids • There are four types of solid: 1. Molecular (formed from molecules) - usually soft with low melting points and poor conductivity. 2. Covalent network -veryhardwithveryhigh melilting points and poor condiiductivity. 3. Ionic (formed form ions) - hard, brittle, high melting poitintsand poor condtiitductivity. 4. Metallic (formed from metal atoms) - soft or hard, high melting points, good conductivity, malleable and ductile. – NB: A solid with only one type of atom is also called ‘atomic’ Copyright © Houghton Mifflin Company. All rights reserved. 16a–1 Copyright © Houghton Mifflin Company. All rights reserved. 16a–2 Bonding in Solids Bonding in Solids Covalent Network Solids Covalent Network Solids • Intermolecular forces: dipole-dipole, London dispersion and H- bonds. • Atoms held together in large networks. • Exampp,gp,q(les: diamond, graphite, quartz (SiO2), silicon carbide ( SiC), and boron nitride (BN). • In diamond: – each C atom has a coordination number of 4; – each C atom is tetrahedral; – there is a three -dimensional array of atoms. – Diamond is hard, and has a high melting point (3550 °C). Copyright © Houghton Mifflin Company. All rights reserved. 16a–3 Copyright © Houghton Mifflin Company. All rights reserved. 16a–4 Diamond -Hard Structure - Tetrahedral atomic arrangement What hybrid state do you think the carbon has? Copyright © Houghton Mifflin Company. All rights reserved. 16a–5 Copyright © Houghton Mifflin Company. All rights reserved. 16a–6 Bonding in Solids Covalent Network Solids • In graphite – each C atom is arranged in a planar hexagonal ring; – layers of interconnected rings are placed on top of each other; – the distance between C atoms is close to benzene (1.42 ÅÅÅ vs.
    [Show full text]
  • Chemical Bonding in Crystals: New Directions
    Z. Kristallogr. 220 (2005) 399–457 399 # by Oldenbourg Wissenschaftsverlag, Mu¨nchen Chemical bonding in crystals: new directions Carlo Gatti* CNR-ISTM Istituto di Scienze e Tecnologie Molecolari, via Golgi 19, 20133 Milano, Italy Received November 8, 2004; accepted January 3, 2005 Chemical bonding / Crystals / Topological descriptors / Introduction QTAIMAC Quantum Theory of Atoms in Molecules and Crystals / ELF Electron Localization Function / Studies of chemical bonding in solids have experienced a Computational crystallography true blossoming over the past decade. The situation has clearly changed since when, in 1988, Roald Hoffman pro- Abstract. Analysis of the chemical bonding in the posi- vocatively observed [1] that “many solid chemists have tion space, instead of or besides that in the wave function isolated themselves from their organic or even inorganic (Hilbert) orbital space, has become increasingly popular for crystalline systems in the past decade. The two most colleagues by choosing not to see bonds in their materi- frequently used investigative tools, the Quantum Theory of als”. Many are the reasons behind this change and many Atoms in Molecules and Crystals (QTAIMAC) and the are the grafts from other scientific disciplines that have Electron Localization Function (ELF) are thoroughly dis- contributed to renovating the interest towards a local de- cussed. The treatment is focussed on the topological pecu- scription of bonding in solids beyond the tremendously liarities that necessarily arise from the periodicity of the successful, though empirical, Zintl–Klemm concept [2–4]. crystal lattice and on those facets of the two tools that A reason, on the one hand, is the continuously increasing have been more debated, especially when these tools are complexity (and reduced size) of new materials and the applied to the condensed phase.
    [Show full text]
  • Chapter 6 Cohesion (Bonding) in Solids
    Chapter 6 Cohesion (Bonding) in Solids 6.1 Introduction Solids often adopt well ordered crystalline structures with well defined lattice constants. Having discussed the many-body Hamiltonian of a solid and its calculation in some detail in previous chapters, it is now natural to ask why a given element chooses a particular crystal structure, and what kind of properties are connected with it. In particular, what types and strengths of forces, i.e. what bonds hold the solid together. This topic is called ’cohesion’ and it is very much to do with the nature of chemical bonding in solids. Just like in all previous chapters, we will restrict ourselves to the situation T 0K, i.e. suffi- ciently low temperatures. This is because at higher temperatures, the properties≈ of matter do not only follow from the total energy alone, but are also governed by other free energy contri- butions. Differing vibrational properties of different crystalline structures can induce structural phase transitions to other configurations upon heating. In fact most elements switch their crystal structure several times before they melt. Another issue is the configurational entropy e.g. due to defects such as vacancies interstials, and impurities. At low enough temperatures, however, the cohesive properties follow predominantly from the chemical binding in a perfect lattice, i.e. from the electrostatic interaction of the electron density with the ions and the ion-ion interac- tion. And this is what we will study in this chapter. The central property of low temperature cohesion is the cohesive energy Ecoh, which is the en- ergy needed to rip a sample apart into widely separated atoms.
    [Show full text]
  • Bonding in Solids & Crystal Structures and X-Ray Diffraction
    UNIT 1 Bonding in Solids & Crystal Structures and X-ray Diffraction 1.1 BONDING IN SOLIDS 1.1.1 INTRODUCTION The most convenient basis for solid state theory is a classification scheme based on the character of the interatomic bonding forces in various classes of crystalline materials. According to this scheme of classification, all solids fall into one of the five general categories: molecular, ionic, covalent, metallic and hydrogen bonded crystals. The distinction is not a sharp one, because some may belong to more than one class. It is a too fundamental fact that inert gases like helium, neon, argon, etc. exist in the atomic form and not easily combine with other atoms to form new compounds because of the magic number 2 in Helium and 8 in other cases. Interatomic force among the atoms in a solid is one of the tools to classify the solids and then to study their physical properties. 1.1.2 FORCES BETWEEN ATOMS AND BOND ENERGY The attractive electrostatic interaction between the electrons and positive charge of the nuclei is totally responsible to group them and then for holding together. Gravitational forces and magnetic forces are negligible compared with the said interaction. When two atoms (or ions) come close to one another, there will be repulsion between negatively charged electrons of both atoms. The repulsive force increases very rapidly as the distance of separation decreases. However when the distance of separation is large, there is attraction between positive nucleus and negative electrons. At some optimum distance (say r = ro), the attractive and repulsive forces just balance and hence the resultant force becomes 2 Applied Physics zero.
    [Show full text]
  • Bonding in Solids
    Module 6 : PHYSICS OF SEMICONDUCTOR DEVICES Lecture 32 : Bonding in Solids Objectives In this course you will learn the following Bonding in solids. Ionic and covalent bond. Structure of Silicon Concept of effective mass. Bonding in Solids Crystals can be classified on the basis of bonding of atoms to form a solid. There are primarily four types of bonding in solids, viz., molecular, ionic, covalent and metallic bonds. Molecular solids are formed by weak inter-molecular forces between molecules. Because of weak binding, the solids have low melting points Metallic solids are characterized by free electrons which move freely through the crystal being bonded to different atoms at different times. Ionic Bond In ionic solids, one of the specis of atoms donates electrons to another specis so that each of the atoms may become more stable by having a noble gas (octet) configuration of electrons. For instance in sodium chloride crystal, Sodium with an atomic number 11 has an electronic configuration while chlorine with the atomic number 17 has the configuration . When the atoms come together, Na gives away one electron and becomes positively ionized while Cl receives one electron and acquires a net negative charge. The negative an the positive ions are held together by electrostatic interaction. Ionic solids are hard, brittle, have high melting points and are poor electrical conductors. Covalent Bond Atoms can also achieve stable octet configuration by sharing of electrons. For instance, in forming hydrogen molecule a pair of hydrogen atoms share two electrons. Other examples of covalent bonded crystals are diamond, graphite, quartz (SiO ) etc.
    [Show full text]
  • Part II: Bonding in Solids 1 Van Der Waals Bonds
    Part II: Bonding in solids Since we are now familiar with the elements and their properties, we can start to discuss how they can be put together to create bigger structures – ultimately, we’re interested in crystalline solids. 1 Van der Waals bonds Let’s start with the noble elements, from group 8, and consider what are the possible interactions between two such atoms, for example two Ne atoms. At first sight, it would be tempting to say that they don’t interact at all with one another. As we’ve seen, because they have completely filled shells, they have very large ionization energies (it’s very hard to remove an electron away from them) and vanishing electron affinity (they don’t want an extra electron). So each Ne keeps its electrons in a filled spherical atomic shell, and what we have are two charge-neutral objects and no interactions (apart from gravitational attraction which is so weak that we can safely ignore it). This is not true, though. First, if we force the atoms close together by making the distance r between them smaller and smaller, it is clear that at some point the electronic clouds will start to overlap and at that point we should have very strong repulsion between them. This is because, according to Pauli’s principle, we can’t have electrons in the same place with the same spin, and that’s exactly what overlap of the electronic clouds would do if the electrons stay undisturbed in their inner shells. So when we bring the atoms close together, some of the electrons have to go into higher energy states and rearrange themselves to stay out of each other’s way, and this costs a lot of energy, leading to strong repulsion at very short distances.
    [Show full text]