Group 2 Compounds

3 Key excerpts on "Group 2 Compounds"

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  eBook - ePub

  Regents Chemistry--Physical Setting Power Pack Revised Edition

  • Albert S. Tarendash(Author)
  • 2021(Publication Date)
  • Barrons Educational Services

    (Publisher)

  Pages 256–258 )

  9.6

  Concept: For Groups 1, 2, and 13–18 in the Periodic Table, elements within the same group have the same number of valence electrons (helium is an exception) and, therefore, have similar chemical properties. (Page 244 )

  Skill: Given the chemical formula of a compound (such as XCl or XCl2 ), determine the group of an element (X). (Pages 256–258 )

  9.7

  Concept: The succession of elements within the same group demonstrates characteristic trends: differences in atomic radius, ionic radius, electronegativity, first ionization energy, and metallic (or nonmetallic) properties. (Pages 248–255 )

  Skill: Compare and contrast the properties of elements within a single group (Groups 1, 2, 13–18) in the Periodic Table. (Pages 248–255 )

  9.8

  Concept: The succession of elements across the same period demonstrates characteristic trends: differences in atomic radius, ionic radius, electronegativity, first ionization energy, and metallic (or nonmetallic) properties. (Pages 248–255 )

  Skill: Compare and contrast the properties of elements across a period (for Groups 1, 2, 13–18) in the Periodic Table. (Pages 249–258 )

  9.9

  Concept: When an atom gains one or more electrons, its radius increases. When an atom loses one or more electrons, its radius decreases. (Page 247 )

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  9.1 INTRODUCTION

  The first question we need to ask is this: Why do we have a Periodic Table of the Elements? The term periodic means that a quantity repeats itself at regular intervals. For example, the motion of the Moon around Earth is periodic because, after a certain length of time (1 month), the motion repeats itself. As early as the Middle Ages, scientists recognized that elements could be differentiated by their physical and chemical properties. These properties are also periodic—if we list the elements properly.

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  eBook - ePub

  Inorganic Chemistry For Dummies

  • Michael Matson, Alvin W. Orbaek(Authors)
  • 2013(Publication Date)
  • For Dummies

    (Publisher)

  Chapter 2 for more details on ionization energies.)

  Figure 12-1: Main group elements on the periodic table.

  When looking at each element, it may help to think about how that group forms bonds with other elements. Here are a few simple questions to ask yourself that can help you understand how each element behaves:

  How well does the element bond to itself? For example, C-C bonding versus F-F bonding.

  How well does it bond to hydrogen? Does it make hydrides, and, if so, what kind of interesting properties can we observe?

  How does it bond to the halogen group? (The halogens bond to nearly every single atom, and so they are often used as a comparison to demonstrate material properties.)

  How does it bond to metals? And if it is a metal atom, how does it bond to nonmetals?

  How does it react to oxygen and carbon? Both oxides and carbides form a large class of materials in and of themselves.

  Ask yourself these simple questions as you look at each group (and then each element), and you start to see the larger picture of how the elements are related to one another. Lucky 13: The Boron Group

  Group 13 elements, also called the boron group, include a wide variety of properties. Some of the important properties about this group include:

  They readily form Lewis acids, three coordinate compounds that are capable of accepting an electron pair and increasing the coordination number.

  All the Group 13 elements have the outer configuration of ns2 np1 . (Chapter 2 covers electron configurations if need a refresher.)

  Most of the boron group elements exhibit a tripositive (3+) oxidation state; however, they can be occasionally found in a unipositive (1+) state (with the exception of boron itself, which we describe in more detail later in this chapter). Keep reading to find out the details of five of the Group 13 (the 13th column on the periodic table) elements: boron, aluminum, gallium, indium, and thallium.

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  eBook - ePub

  Geochemistry

  Pathways and Processes

  • Harry McSween, Steven Richardson, Maria Uhle(Authors)
  • 2003(Publication Date)
  • Columbia University Press

    (Publisher)

  figure 2.12 , contains elements that, by virtue of their common electron configuration, behave in similar ways during chemical reactions and therefore form similar compounds.

  FIG. 2.11. As electrons are removed from an atom, the remaining electrons are drawn more tightly by the charge of the nucleus, so that ionic radius decreases with increasing positive charge. Compare, for example, the radii of Fe2+ and Fe3+ or Mn2+ and Mn4+ . Also, compare each of the ionic radii in this figure with the atomic radii in figure 2.9 .

  Appreciation for the periodic properties of the elements has cast light on many geochemical mysteries. One of the most fundamental observations that geologists make about the Earth, for example, is that it is a differentiated body with a core, mantle, and crust that are chemically distinct. Why? Is there a rational way to explain why such elements as potassium, calcium, and strontium are concentrated in the crust and not in the core? Or why copper is almost invariably found in sulfide ores rather than in oxides?

  FIG. 2.12. Elements with similar properties fill similar roles in nature and are therefore commonly recognized as members of groups, as indicated in this figure. The lanthanides are often referred to as rare earth elements (REE).

  Early in the twentieth century, Victor Goldschmidt was prompted by a study of differentiated meteorites to propose a practical scheme for grouping elements according to their mode of occurrence in nature. His analyses of three kinds of materials—silicates, sulfides, and metals—suggested that most elements have a greater affinity for one of these three materials than for the other two. Calcium, for example, can be isolated as a pure metal with great difficulty, and its rare sulfide, oldhamite (CaS), occurs in some meteorites. Calcium is most common, however, in silicate minerals. Gold, however, is almost invariably found as a native metal.

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