Physics
Chemical Bonds
Chemical bonds are the forces that hold atoms together in molecules. These bonds are formed through the sharing or transfer of electrons between atoms. The main types of chemical bonds include covalent bonds, where electrons are shared, and ionic bonds, where electrons are transferred from one atom to another.
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12 Key excerpts on "Chemical Bonds"
- Robert J. Naumann(Author)
- 2008(Publication Date)
- CRC Press(Publisher)
3 Chemical Bonding The ability of atoms and molecules to form Chemical Bonds is the de fi ning feature of the structure and properties of solids. The types of bonds that are formed determine if the material will be a metal, a ceramic, or a polymer, and whether the material will conduct electricity, transmit light, or be magnetic. 3.1 What Holds Stuff Together? All matter that we deal with on an everyday basis is held together by electrical forces that form Chemical Bonds. These forces are manifested in different ways, depending upon which elements are involved. There are three type of primary bonds: (1) the metallic bond in which electrons become detached from atoms when they come together so the ion cores become mutually attracted to the sea of electrons surrounding them; (2) the covalent bond in which atoms become mutually attracted by sharing electrons in order to form closed electron shells; and (3) the ionic bond in which a mutual attraction occurs when one or more electrons leaves a metal atom to complete an atomic shell of a nonmetallic atom forming an oppositely charged ion pair. Much weaker bonds, such as the hydrogen bond, which arise from dipolar attractions between molecules when a hydrogen atom becomes covalently bonded to an O, N, or F atom, or to the van der Waals bond, which arises from induced dipole – dipole interactions, play a secondary role in the structure of materials. Understanding these basic forces that hold materials together is crucial to understanding the structure and properties of materials. We shall start with the ionic bond since conceptu-ally it is the easiest to visualize and it lends itself to a simple analytical model. 3.2 Ionic Bonding The ionic bond is the strongest chemical bond, ranging from 10.5 eV for LiF to 5.8 eV for CsI, but it can only act between two (or more) dissimilar atoms.
eBook - ePub- Sir Alan Cottrell(Author)
- 2019(Publication Date)
- CRC Press(Publisher)
Chapter 4Chemical Bonding
4.1 Forces between atoms
The physical meaning of chemical affinity is that an attractive force exists between the atoms. There is also a repulsive force at close range which is the basis of the ‘impenetrability’ of matter. The equilibrium spacing of a pair of atoms is that at which these two forces are equal. Because force is rate of change of energy with distance, the energy of interaction of the pair reaches its lowest value at the equilibrium spacing. Quantum mechanics deals directly with energy, not force, and so it is usual to discuss problems of chemical bonding in terms of energy.We bring two atoms together from infinity, having defined their potential energy of interaction as zero at infinity. Little happens and the energy stays near zero until the atoms are within about an atomic spacing of each other. As they move still closer, the attractive force begins to be felt and the potential energy falls, since work is being done by the atoms as they move together under this force. When they get really close, the short-range repulsive force then also comes into play and soon dominates the attractive force. The potential energy rises at this stage since the atoms are now being pushed together. This behaviour is shown in Fig. 4.1 which gives the potential energy due to the attractive (curve a), repulsive (curve b) and total (curve c) forces as a function of the distance between nuclei. The potential energy ‘well’ is deepest at the equilibrium spacing r and its depth D there is equal to the work required to dissociate the atoms completely.Whether a collection of such atoms will form a gas or condense together into a liquid or solid depends both on D (in relation to the temperature and pressure) and on the nature of the forces. Molecular gases can form even when D is large (e.g. H2 , O2 , N2 , CO2 , at room temperature) if the atomic forces show saturation
eBook - PDF- Brian W. Pfennig(Author)
- 2021(Publication Date)
- Wiley(Publisher)
4 An Introduction to Chemical Bonding “A bond does not really exist at all—it is a most convenient fiction.” —Charles Coulson 4.1 THE DEFINITION OF A CHEMICAL BOND Almost every chemical reaction involves the making and/or breaking of a chemical bond. Despite its central importance in the lexicon of chemistry, there continues to be a healthy debate about what a bond actually is, so much so that the British theoretician, Charles Coulson, once quipped that “a bond does not really exist at all—it is a most convenient fiction.” Suppose that I asked my students for their definition of a chemical bond. I imagine that many of them might turn to the fountain of all knowledge known as Wikipedia for a definition. Going straight to the source myself, Wikipedia defines a chemical bond as “a lasting attraction between atoms that enables the formation of a chemical compound,” a circular argument if ever there was one. The Collins English dic- tionary has only a slightly better answer, defining a bond as “a mutual attraction between two atoms resulting from a redistribution of their outer electrons.” Dissatisfied with either of these definitions, I thought I would turn to the OG himself—Gilbert Newton Lewis, who is arguably the godfather of the chemical bond.
eBook - PDFThe Sciences
An Integrated Approach
- James Trefil, Robert M. Hazen(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
In exactly the same way, when two or more atoms come together the electrons tend to rearrange themselves to minimize the chemical potential energy of the entire system. his situation may require that they exchange or share electrons. Usually, that process involves rearrangements with a total of 2, 10, 18, or 36 electrons. Chemical Bonds result from any redistribution of electrons that leads to a more stable coniguration between two or more atoms—especially conigurations with a illed electron shell. • Most atoms adopt one of three simple strategies to achieve a filled shell: they give away electrons, accept electrons, or share electrons. If the bond formation takes place spontaneously, without outside intervention, energy will be released in the reaction. he burning of wood or paper (once their temperature has been raised high enough) is a good example of this sort of pro- cess, and the heat you feel when you put your hands toward a ire derives ulti- mately from the chemical potential energy that is given of as electrons and atoms are reshuled. Alternatively, atoms may be pushed into new conigurations by adding energy to systems. Much of industrial chemistry, from the smelting of iron to the synthesis of plastics, operates on this principle. 1 H 1.00794 3 Li 6.941 4 Be 9.01218 11 Na 22.98977 12 Mg 24.3050 2 He 4.00260 5 B 10.811 6 C 12.011 7 N 14.00674 8 O 15.9994 9 F 18.99840 10 Ne 20.1797 13 Al 26.98154 14 Si 28.0855 15 P 30.97376 16 S 32.066 17 Cl 35.4527 18 Ar 39.948 FIGURE 10-1 The first three rows of the periodic table, containing elements 1 and 2, 3 through 10, and 11 through 18, respectively, hold the key to understanding chemical bonding. 211 10.3 TYPES OF Chemical Bonds 10.3 Types of Chemical Bonds Atoms link together by three principal kinds of Chemical Bonds—ionic, metallic, and covalent— all of which involve redistributing electrons between atoms.
eBook - PDF- Michael R Fisch(Author)
- 2004(Publication Date)
- WSPC(Publisher)
This means the atoms experience a force “pulling them together” when they are separated by a distance greater than re. In fact, we know that the form of the force shown above must be es- sentially correct. First, an attractive force must exist; otherwise, Chemical Bonds between atoms would not form, and we know that compounds exist. That compounds exist tells us that the interatomic force is attractive at large enough distances (although it does not address the issue of its mathe- matical equation or “functional form”). The fact that matter does not col- lapse means that there must be a force preventing this collapse to a lower energy state. Thus, the force must be repulsive at very small separations. The repulsive part of the interaction is largely due to the positively charged nuclei repeUing each other and a quantum mechanical principle known as the Pauli exclusion principle. Experiments also indicate that there is an equilibrium separation or bond length between chemically bonded atoms. This equilibrium bond length must correspond to zero force. To understand Chemical Bonds, it helps to understand a little more about electrons in atomic orbitals, orbital electrons for short. A careful examination of the periodic table (see Fig. 6.7) indicates that as one moves in a row (or period) from left to right, the orbitals become filled with more and more electrons. A special class of atoms forms the last column (VIIIA) of the periodic table. The atoms in this column have totally filled orbitals. These atoms are called the noble or inert gases, because they have very low reactivity or “low chemical affinity.” There are very few compounds formed from inert gases, and for a long time there were no known compounds formed with this class of atoms. Because of this experimental fact and detailed study, it is known that completely filled orbitals are (a) spherical, (b) particularly stable and (c) associated primarily with repulsion.
eBook - PDF- George C. King(Author)
- 2023(Publication Date)
- Wiley(Publisher)
2 The forces that bind atoms together At the beginning of Chapter 1, we made the statement that atoms attract each other when they are a little distance apart, but repel when they are squeezed together. Evidence that atoms are attracted to each other comes from the fact that atoms combine together to form solids and liquids. Evidence that atoms repel each other comes from the fact that solids and liquids resist being compressed. These physical properties arise from the forces that act between the atoms. These forces and the resulting bonding of the atoms are the subjects of the present chapter. We will describe the general characteristics of the forces that bind atoms together and the resulting potential energy of the atoms. And we will describe the principal kinds of inter- atomic bonding: van der Waals, ionic, covalent, and metallic bonding. We will see that all bonding is a con- sequence of the electrostatic interaction between nuclei and electrons. And we will see that the interatomic interactions that we will describe on the microscopic scale relate directly to the properties of matter that are observed in the laboratory. 2.1 General characteristics of interatomic forces Before going into detail about particular types of interatomic force, we describe some general features of such forces. We are interested in whether the force acting between atoms is attractive or repulsive. We are also interested in the way the strength of the force varies with interatomic separation. To discuss these two aspects, we imagine an atom fixed in place at the origin (r = 0) of a coordinate system and a second atom a distance r away, where r is the distance between the centres of the two atoms. This arrangement is illus- trated in Figure 2.1. We make the assumption that the force depends only on distance r. If the force is repul- sive, the force acts to increase the separation of the two atoms, i.e.
Alternatively, atoms may be pushed into new configurations by adding energy to systems. Much of industrial chemis- try, from the smelting of iron to the synthesis of plastics, operates on this principle. 1 H 1.00794 3 Li 6.941 4 Be 9.01218 11 Na 22.98977 12 Mg 24.3050 2 He 4.00260 5 B 10.811 6 C 12.011 7 N 14.00674 8 O 15.9994 9 F 18.99840 10 Ne 20.1797 13 Al 26.98154 14 Si 28.0855 15 P 30.97376 16 S 32.066 17 Cl 35.4527 18 Ar 39.948 Figure 10-1 • The first three rows of the periodic table, containing elements 1 and 2, 3 through 10, and 11 through 18, respectively, hold the key to understanding chemical bonding. Types of Chemical Bonds Atoms link together by three principal kinds of Chemical Bonds—ionic, metallic, and covalent—all of which involve redistributing electrons between atoms. In addition, polar- ization, hydrogen bonding, and van der Waals forces result from shifts of electrons within their atoms or groups of atoms. Each type of bonding corresponds to a different way of rearranging electrons, and each produces distinctive properties in the materials it forms. Types of Chemical Bonds | 209 IONIC BONDS We’ve seen that atoms with “magic numbers” of 2, 10, 18, or 36 electrons are particu- larly stable. By the same token, atoms that differ from these magic numbers by only one electron in their outer orbits are particularly reactive—in effect, they are “anxious” to fill or empty their outer orbits. Such atoms tend to form ionic bonds, Chemical Bonds in which the electrical force between two oppositely charged ions holds the atoms together. Ionic bonds often form as one atom gives up an electron while another receives it. Sodium (a soft, silvery white metal), for example, has 11 electrons in an electrically neutral atom—2 in the lowest orbit, 8 in the next, and a single electron with lots of chemical potential energy in its outer shell. Sodium’s best bonding strategy, therefore, is to lose one electron.
eBook - PDFFundamentals of Materials Science and Engineering
An Integrated Approach
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
For each type, the bonding necessarily involves the valence electrons; furthermore, the nature of the bond depends on the electron structures of the constitu- ent atoms. In general, each of these three types of bonding arises from the tendency of the atoms to assume stable electron structures, like those of the inert gases, by com- pletely filling the outermost electron shell. Secondary or physical forces and energies are also found in many solid materials; they are weaker than the primary ones but nonetheless influence the physical properties of some materials. The sections that follow explain the several kinds of primary and secondary interatomic bonds. primary bond Ionic Bonding Ionic bonding is perhaps the easiest to describe and visualize. It is always found in compounds composed of both metallic and nonmetallic elements, elements situated at the horizontal extremities of the periodic table. Atoms of a metallic element easily give up their valence electrons to the nonmetallic atoms. In the process, all the atoms acquire stable or inert gas configurations (i.e., completely filled orbital shells) and, in addition, an electrical charge—that is, they become ions. Sodium chloride (NaCl) is the classic ionic material. A sodium atom can assume the electron structure of neon (and a net single positive charge with a reduction in size) by a transfer of its one va- lence 3s electron to a chlorine atom (Figure 2.11a). After such a transfer, the chlorine ion acquires a net negative charge, an electron configuration identical to that of argon; it is also larger than the chlorine atom. Ionic bonding is illustrated schematically in Figure 2.11b. The attractive bonding forces are coulombic—that is, positive and negative ions, by virtue of their net electrical charge, attract one another.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 2 Chemical Physics Chemical physics is a subdiscipline of chemistry and physics that investigates physic-cochemical phenomena using techniques from atomic and molecular physics and condensed matter physics; it is the branch of physics that studies chemical processes from the point of view of physics. While at the interface of physics and chemistry, chemical physics is distinct from physical chemistry in that it focuses more on the characteristic elements and theories of physics. Meanwhile, physical chemistry studies the physical nature of chemistry. Nonetheless, the distinction between the two fields is vague, and workers often practice in each field during the course of their research. What chemical physicists do Chemical physicists commonly probe the structure and dynamics of ions, free radicals, polymers, clusters, and molecules. Areas of study include the quantum mechanical behavior of chemical reactions, the process of solvation, inter- and intra-molecular energy flow, and single entities such as quantum dots. Experimental chemical physicists use a variety of spectroscopic techniques to better understand hydrogen bonding, electron transfer, the formation and dissolution of Chemical Bonds, chemical reactions, and the formation of nanoparticles. Theoretical chemical physicists create simulations of the molecular processes probed in these experiments to both explain results and guide future investigations. The goals of chemical physics research include understanding chemical structures and reactions at the quantum mechanical level, elucidating the structure and reactivity of gas phase ions and radicals, and discovering accurate approximations to make the physics of chemical phenomena computationally accessible.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 6 Chemical Physics Chemical physics is a subdiscipline of chemistry and physics that investigates phy-sicochemical phenomena using techniques from atomic and molecular physics and condensed matter physics; it is the branch of physics that studies chemical processes from the point of view of physics. While at the interface of physics and chemistry, chemical physics is distinct from physical chemistry in that it focuses more on the characteristic elements and theories of physics. Meanwhile, physical chemistry studies the physical nature of chemistry. Nonetheless, the distinction between the two fields is vague, and workers often practice in each field during the course of their research. What chemical physicists do Chemical physicists commonly probe the structure and dynamics of ions, free radicals, polymers, clusters, and molecules. Areas of study include the quantum mechanical behavior of chemical reactions, the process of solvation, inter- and intra-molecular energy flow, and single entities such as quantum dots. Experimental chemical physicists use a variety of spectroscopic techniques to better understand hydrogen bonding, electron transfer, the formation and dissolution of Chemical Bonds, chemical reactions, and the formation of nanoparticles. Theoretical chemical physicists create simulations of the molecular processes probed in these experiments to both explain results and guide future investigations. The goals of chemical physics research include understanding chemical structures and reactions at the quantum mechanical level, elucidating the structure and reactivity of gas phase ions and radicals, and discovering accurate approximations to make the physics of chemical phenomena computationally accessible.
eBook - PDFFundamentals of Materials Science and Engineering
An Integrated Approach
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
Secondary or physical forces and energies are also found in many solid materials; they are weaker than the primary ones but nonetheless influence the physical properties of some materials. The sections that follow explain the several kinds of primary and secondary interatomic bonds. bonding energy primary bond 2.6 | | PRIMARY INTERATOMIC BONDS Ionic Bonding Ionic bonding is perhaps the easiest to describe and visualize. It is always found in compounds composed of both metallic and nonmetallic elements, elements situated at the horizontal extremities of the periodic table. Atoms of a metallic element easily give up their valence electrons to the nonmetallic atoms. In the process, all the atoms acquire stable or inert gas configurations (i.e., completely filled orbital shells) and, in addition, an electrical charge—that is, they become ions. Sodium chloride (NaCl) is the classic ionic material. A sodium atom can assume the electron structure of neon (and a net single positive charge with a reduction in size) by a transfer of its one va- lence 3s electron to a chlorine atom (Figure 2.13a). After such a transfer, the chlorine ion acquires a net negative charge, an electron configuration identical to that of argon; ionic bonding 2.6 Primary Interatomic Bonds 35 it is also larger than the chlorine atom. Ionic bonding is illustrated schematically in Figure 2.13b. The attractive bonding forces are coulombic—that is, positive and negative ions, by virtue of their net electrical charge, attract one another. For two isolated ions, the attrac- tive energy E A is a function of the interatomic distance according to E A = − A __ r (2.9) Theoretically, the constant A is equal to A = 1 ____ 4 π ε 0 (|Z 1 |e)(|Z 2 |e) (2.10) Here ε 0 is the permittivity of a vacuum (8.85 × 10 −12 F/m), |Z 1 | and |Z 2 | are absolute values of the valences for the two ion types, and e is the electronic charge (1.602 × 10 −19 C).
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Library Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 1 Chemical Physics and Physical Chemistry Chemical physics Chemical physics is a subdiscipline of chemistry and physics that investigates physi-cochemical phenomena using techniques from atomic and molecular physics and condensed matter physics; it is the branch of physics that studies chemical processes from the point of view of physics. While at the interface of physics and chemistry, chemical physics is distinct from physical chemistry in that it focuses more on the characteristic elements and theories of physics. Meanwhile, physical chemistry studies the physical nature of chemistry. Nonetheless, the distinction between the two fields is vague, and workers often practice in each field during the course of their research. What chemical physicists do Chemical physicists commonly probe the structure and dynamics of ions, free radicals, polymers, clusters, and molecules. Areas of study include the quantum mechanical behavior of chemical reactions, the process of solvation, inter- and intra-molecular energy flow, and single entities such as quantum dots. Experimental chemical physicists use a variety of spectroscopic techniques to better understand hydrogen bonding, electron transfer, the formation and dissolution of Chemical Bonds, chemical reactions, and the formation of nanoparticles. Theoretical chemical physicists create simulations of the molecular processes probed in these experiments to both explain results and guide future investigations. The goals of chemical physics research include understanding chemical structures and reactions at the quantum mechanical level, elucidating the structure and reactivity of gas phase ions and radicals, and discovering accurate approximations to make the physics of chemical phenomena computationally accessible.
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