3 Key excerpts on "Bond Length"

• 

  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)

  4

  Atomic structure and chemical bonding

  A  The idea of valency

  B  The structure of atoms

  B1  The electrical connection

  B2  The composition of atoms

  B3  The atomic nucleus, mass numbers and isotopes

  B4  The electron structure of atoms

  C  Bonding mechanisms

  C1  Covalency: bonding by sharing

  C2  Ions: bonding by electron transfer

  C3  Bonding in metals

  D  Physical properties related to bonding

  Atomic structure and chemical bonding

  The idea that atoms are able to bond together to form molecules will be quite familiar to you by now. However, so far, nothing has been explained about why this should happen. By taking a closer look at the basic structure common to all atoms and then at their electrical properties it will become possible for you to see why atoms of one element behave in a different way to those of any other kind. This chapter will also explain the several different ways atoms can bond together, helping to reveal how this relates to a variety of physical and chemical properties displayed by the compounds and elements that you work with.

  A The idea of valency

  valency

  In the last chapter you learnt that the atomic mass of an element is one characteristic feature of its atoms. The structural formulae introduced in Chapter 3 revealed another characteristic; the number of links or bonds which one atom can make with others. The number of bonds that a single atom of an element can make is known as its valency. For many elements this is a constant number. The equation for the reaction which was used as an example earlier on

  the burning of methane gas, used four kinds of molecules with these structures:

  Figure 4.1 Structural formulae of molecules involved in the burning of natural gas.

  double bond

  In these structures the number of dashes (which indicate bonds) emerging from each kind of atom is seen to be constant. Hydrogen is always joined to the next atom by one dash representing a single bond. Oxygen always makes two bonds and carbon always four. To indicate these characteristic numbers, the structures sometimes show two bonds between one pair of atoms: a double bond

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  eBook - ePub

  Understanding General Chemistry

  • Atef Korchef(Author)
  • 2022(Publication Date)
  • CRC Press

    (Publisher)

  8 Chemical Bonding and Molecular Geometry

  DOI: 10.1201/9781003257059-8

  8.1 Objectives

  At the end of the present chapter, the student will be able to:

  1. Recognize the different types of chemical bonding.
  2. Draw the Lewis structure of different atoms and ions.
  3. Recognize the different molecular geometries.
  4. Determine the geometry of molecules.

  8.2 Chemical Bonding

  Chemical bonding (intramolecular forces) is defined as the attractive forces that hold two or more chemical constituents (atoms and ions) together in different chemical species. The electrons involved in bonding are usually those in the outermost (valence) shell.

  There are three types of chemical bonds:

  1. Covalent bonds result from sharing electrons between the atoms. The covalent bond is usually found between non-metals. Depending on the electronegativities of the atoms involved in the bond, the covalent bond can be polar or non-polar (Figure 8.1 ). Polar covalent bonds occur when the difference in electronegativity between the two constituent atoms is between 0.4 and 2.  Examples of polar covalent bonds: The bond between hydrogen and chlorine in HCl is a polar covalent bond. Chlorine (Cl) is more electronegative than hydrogen (H). The shared pair of electrons between Cl and H is attracted toward the chlorine atom. Because of this, the hydrogen atom has a partially positive charge (δ+ ) and the chlorine atom has a partially negative charge (δ− ). In addition, the bond between hydrogen and bromine in HBr, the bond between hydrogen and fluorine in HF and the bond between hydrogen and oxygen in water H2 O are polar covalent bonds.  Examples of non-polar covalent bonds: The bond between two iodine atoms in I2 is a non-polar covalent bond. The bonds between hydrogen (H) and carbon (C) in CH4 are non-polar covalent bonds.  Note that the non-polar covalent bond is found in homonuclear molecules such as Br2 , Cl2 , O2 , I2 and in hydrocarbons (Cn H2n + 2

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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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