8 Key excerpts on "Chemical Bonds"

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  eBook - ePub

  AP® Chemistry All Access Book + Online + Mobile

  • Kevin Reel, Derrick C. Wood, Scott A. Best(Authors)
  • 2014(Publication Date)
  • Research & Education Association

    (Publisher)

  6

  Chemical Bonding

  Intramolecular Forces: Bonds Between Atoms

  Bonds are the forces of attraction that hold atoms together. There are many types of bonding including ionic, metallic, and covalent bonds. You can figure out the difference between the bonding types if you look at what role the valence electrons are playing in the chemical bond—because bonding is all about the valence electrons. Many of the electrons in an atom have no impact on bonding because they are located close to the nucleus, and thus are called core electrons . In general, the valence electrons are the outermost s-shell and p-shell electrons in an electron configuration. For transition metals, the outermost d-shell electrons will also play a role. Elements will typically form bonds in order to have eight electrons in the valence shell, which is called the octet rule . The vast majority of Chemical Bonds that occur obey the octet rule, although a significant number of exceptions to the octet rule exist; these exceptions will be covered later in this chapter.

  Ionic Bonds

      •   Ionic bonding is a bond between a cation and an anion held together by electrostatic attractions. Coulomb’s law dictates that oppositely charged particles are attracted to one another, and this is the fundamental principle behind ionic bonding.

      •   In an ionic bond, an electron is removed from the least electronegative atom to form a positively charged ion (cation). This electron is then transferred to a more electronegative atom to form a negatively charged ion (anion).

      •   Ionic bonds form in order to fulfill the octet rule for the elements involved with the bond. The metal loses electrons to have a filled shell. The nonmetal gains electrons to have a filled shell.

     

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  eBook - ePub

  Intermolecular and Surface Forces

  • Jacob N. Israelachvili(Author)
  • 2010(Publication Date)
  • Academic Press

    (Publisher)

  3 Strong Intermolecular Forces: Covalent and Coulomb Interactions

  3.1 Covalent or Chemical Bonding Forces

  Like two hydrogen atoms and one oxygen atom that combine to form a water molecule, when two or more atoms come together to form a molecule, the forces that tightly bind the atoms together within the molecule are called covalent forces , and the interatomic bonds formed are called covalent or Chemical Bonds . Closely allied to covalent bonds are metallic bonds. In both cases the bonds are characterized by the sharing of the electrons between the two or more atoms so that the discrete nature of the atoms is lost.

  Depending on the position an atom (or element) occupies in the periodic table, it can participate in a certain number of covalent bonds with other atoms. This number, or stoichiometry, is known as the atomic valency ; for example, it is zero for the inert gases (e.g., argon) that cannot normally form covalent bonds with other atoms—one for hydrogen, two for oxygen, three for nitrogen, and four for carbon and silicon—and thus water H2 O (H—O—H), hexane C6 H12 (H3 C—CH2 —CH2 —CH2 —CH2 —CH3 ), and so on. However, atoms can also form double or triple bonds where more than one electron is shared with a neighboring atom, as in carbon dioxide CO2 (O=C=O) and acetylenic compounds (—CH2 —C C—CH2 —). A further characteristic of covalent bonds is their directionality; that is, they are directed or oriented at well-defined angles relative to each other. Thus, for multivalent atoms, their covalent bonds determine the way they will coordinate themselves in molecules or in crystalline solids to form an ordered three-dimensional lattice. For example, they determine the way carbon atoms arrange themselves to form the perfectly ordered diamond structure. Rotational freedom is another important property of covalent bonds. Thus, the carbon-carbon single bond allows for rotation about the bond, but double and triple bonds do not.1

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  eBook - ePub

  The Science For Conservators Series

  Volume 1: An Introduction to Materials

  • The Conservation Unit Museums and Galleries Commission(Author)
  • 2008(Publication Date)
  • Routledge

    (Publisher)

  The electrons can thus move freely from one atom to another because none of the overlapping outer orbitals is full. In other words, the outer electrons belong to all the atoms. The mobile electrons act as a cohesive force preventing the positive metal ions from pushing each other apart. Just as with the ionic bond there is no distinct group of atoms which can be identified as a molecule. This type of structure can extend indefinitely in any direction. Often the most stable structure (and hence the most likely one) will be that in which there is the greatest overlap of the orbitals of one atom with those of its neighbours. This is achieved in many metals (such as copper, silver, and gold) by a regular pattern called close-packing. The regular array of repeating units in three dimensions suggests that metals are crystalline. It is unusual to see individual metal crystals in isolation, but solid metal objects are made up of large numbers of small crystals joined together. The boundaries between these crystals can be seen under a microscope.

  Figure 4.18 Photomicrograph, showing the individual crystals in a sample of brass – 60% copper, 40% zinc.

  Three types of bond?

  Covalent, ionic and metallic bonds have been described as if they formed three distinct categories. We have seen that really these three are just definable points in a wide range of bonding behaviour.

  Covalent bonding describes not only the equal sharing of an electron pair between two atoms but may involve electron sharing over larger numbers of atoms (as in SO2 ). The extreme form of this is the completely delocalised electron structure of metals.

  In a covalent bond the electrons may not be shared equally between the atoms if one is more electronegative than another (oxygen in H2 O). The extreme form of unequal sharing is when there is complete electron transfer from one atom to another, as is found in the ionic bond.

  D Physical properties related to bonding

  The materials of which objects are made have different physical characteristics which distinguish them from each other. Materials are often chosen for a particular job because of these distinguishing features. Copper, which conducts electricity well, is used in wires to carry current, while plastics such as polyvinyl chloride, which do not conduct electricity, are used as insulation for the copper wire. Solvents with low boiling points are used for dry-cleaning because they will evaporate rapidly from the textile, once the cleaning has been finished.

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  eBook - ePub

  General Chemistry for Engineers

  • Jeffrey Gaffney, Nancy Marley(Authors)
  • 2017(Publication Date)
  • Elsevier

    (Publisher)

  Chapter 3

  Chemical Bonding—The Formation of Materials

  Abstract

  This chapter covers chemical bonding between atoms and ions and how this affects the chemical properties of the elements. Which elements form ions and the typical charges on the ions are explained. Ionic bonding and covalent bonding are compared in terms of the octet rule and valence bond theory. Polar and nonpolar covalent bonds are explained and their relationship to both electron group geometry and molecular geometry is stressed. Polyatomic ions are described as a mixed ionic, covalent species. Molecular orbital theory is introduced to explain magnetism, bond order, and hybridization, which will be important in later discussions of the chemistry of carbon. Intermolecular forces, including hydrogen bonding, are discussed with a special Case Study focusing on the special properties of water.

  Keywords

  Ionic bonding; Covalent bonding; Octet rule; Polyatomic ions; Dipole moment; Molecular orbitals; Hybridization; Resonance; Molecular geometry; Intermolecular forces

  Outline

  3.1  

  Atoms and Ions

  3.2  

  Ionic Bonding

  3.3  

  Covalent Bonding

  3.4  

  Mixed Covalent/Ionic Bonding

  3.5  

  Molecular Orbitals

  3.6  

  Molecular Geometry

  3.7  

  Molecular Polarity

  3.8  

  Intermolecular Forces

  Important Terms

  Study Questions

  Problems

  3.1 Atoms and Ions

  A neutral atom that loses one or more electrons becomes a positively charged ion. This positively charged ion is known as a cation (from the Greek word katá , meaning “down”). A neutral atom that gains one or more electrons has a negative charge and is known as an anion (from the Greek word ánō , meaning “up”). The number of electrons an element will gain or lose is also a periodic property and can generally be predicted from its position in the periodic table as shown in Fig. 3.1 . Atoms will gain or lose electrons to form ions that have electronic configurations which are more stable than the electronic configurations of the parent atoms. For most elements, this means that they will either gain or lose the number of electrons needed to achieve a closed valence shell. Remember from Table 2.9 of Chapter 2

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  eBook - ePub

  Chemistry

  Concepts and Problems, A Self-Teaching Guide

  • Richard Post, Chad Snyder, Clifford C. Houk(Authors)
  • 2020(Publication Date)
  • Jossey-Bass

    (Publisher)

  3 Periodic Properties and Chemical Bonding In Chapter 1 you learned that the elements in a horizontal row of the periodic table show regular variation in properties from left to right. The elements are arranged in the table in order by increasing atomic number (reading the table left to right, line by line, in the way you are reading this paragraph). The reason this arrangement works so well is that all atoms consist of electrons, protons, and neutrons. The neutrons and protons are in the nucleus with electrons arranged in “shells” around the nucleus. Why did we consider the electronic arrangement of atoms in such detail? Because the chemical properties of an element depend upon the number of electrons in its outermost shell, the energy levels of its outermost electrons, and the size of the atom. These details of atomic structure determine what kinds and how many Chemical Bonds can be formed by an atom. In this chapter we discuss several properties not mentioned in Chapter 1 that depend upon the outermost shell electronic structure. We will review electron configuration and introduce new “dot” symbols. We will then discuss whether atoms gain, lose, or share electrons, and how many, when they combine to form new substances. The major portion of the chapter is devoted to the types of Chemical Bonds (ionic, covalent, polar covalent) formed between atoms in chemical compounds

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  eBook - ePub

  Physical Chemistry of Foods

  • Pieter Walstra(Author)
  • 2002(Publication Date)
  • CRC Press

    (Publisher)

  3 Bonds and Interaction Forces

  Atoms, groups of atoms, ions, molecules, macromolecules, and particles always are subject to forces between them. These interaction forces may cause chemical reactions to occur, i.e., cause the formation of other molecular species, but they are also responsible for the existence of condensed phases (solids and liquids), for adherence of a liquid to a solid surface, or for aggregation of particles in a liquid. In short, all structures form because of interaction forces. Generally, formation of a structure causes a decrease in entropy, and this may counteract the tendency of formation, depending on its magnitude compared to that of the energy involved.

  There are several, rather different, types of interaction forces, although all of them are ultimately due to the electromagnetic force. This force can thus become manifest in various ways. The interactions greatly differ in specificity: what group or molecule will interact with what other group etc.? For instance, they all decrease in magnitude with interparticle distance, but the relation between energy and distance may vary widely. One generally considers the energy needed to bring two particles (or molecules, etc.) from infinite distance to close proximity. Since there is always more than one type of force acting, this energy (U) may be negative or positive, depending on the interparticle distance (h), for instance as depicted in Figure 3.1 . The force (F) generally is the derivative of the energy (F=-dU/dh) and, as illustrated in the figure, the net force is thus zero where the energy is at minimum; here we have a stable configuration.

  Table 3.1 gives an overview of the various types of forces. The first one mentioned cannot lead to bond formation, since it is always repulsive. If two atoms approach closely, their electron clouds start to overlap, and this causes a repulsion that increases very steeply with decreasing distance; it is therefore called hard-core repulsion

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  eBook - ePub

  Nursing HESI A2

  a QuickStudy Laminated Reference & Study Guide

  • April Michelle Davis(Author)
  • 2018(Publication Date)
  • QuickStudy Reference Guides

    (Publisher)

  Hydrogen bonding: Hydrogen bonded to electro­negative atoms
• Van der Waals forces: The sum of small force inter­actions between molecules not in covalent, ionic, or hydrogen bonds
• London dispersion force: Temporary dipoles created by the normal movement of electrons