Group 2 Compounds

4 Key excerpts on "Group 2 Compounds"

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  eBook - PDF

  Comparative Inorganic Chemistry

  • Bernard Moody(Author)
  • 2013(Publication Date)
  • Arnold

    (Publisher)

  18 Group II: the alkaline-earth metals Beryllium, magnesium, calcium, strontium and barium The alkaline-earths are a family of very reactive metals in which the electro-positive nature increases sharply with increase in atomic number. Calcium, strontium, bar-ium and radium form a close series of very similar ele-ments and compounds with a steady gradation of proper-ties. Radium, isolated by the Curies in 1898 from pitch-blende, a mineral of uran-ium which showed unex-pectedly high radioactivity, is highly radioactive and while those salts which have been studied show the nor-mal alkaline-earth characteristics, neither the ele-ment nor its compounds will be described further here. Magnesium is somewhat apart from metals which follow it, showing some resemblance to zinc, which heads the other subgroup assigned to Group II. Magnesium and calcium compounds in general use are described in detail as are a few compounds of barium. Strontium and its salts are compara-tively rare. Some compounds of strontium and barium are mentioned to reveal their overall similarity to the corresponding compounds of calcium. Beryllium is very distinctive; it differs from magnesium more than that element differs from the others, and while it undoubtedly belongs to Group II, it resembles the diagonally placed element, aluminium, so much that at one time beryllium was considered to be tervalent. The metals magnesium, calcium, strontium and barium are white, lustrous when freshly exposed but quickly tarnished by the atmosphere, and fairly soft. Barium is usually stored in oil and when finely divided is spontaneously flammable. The melting-points and boiling-points do not follow a regular pattern, while the densities at room temperature decrease from beryllium to calcium and then rise to barium. This is accounted for by differences in crystal structure.

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  Foundations of Chemistry

  An Introductory Course for Science Students

  • Philippa B. Cranwell, Elizabeth M. Page(Authors)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  The term alkaline comes from the pH of the compounds formed from the elements when allowed to react with air or water. The term earth is a historical name given to substances found as ores (for example, metal salts) that are insoluble in water and stable on heating. Many compounds of Group 2 elements fit this description. The periodic table shows the members of Group 2 to consist of beryllium, magnesium, calcium, strontium, barium, and radium. Calcium and magnesium are the sixth and eighth most abundant elements, respectively, in the earth ’ s crust. Box 11.2 As with Group 1, the heaviest member of this group, radium, is radi-oactive. Radium was discovered by Pierre and Marie Curie in 1898. They separated 1 mg of radium from 10,000 kg of pitchblende – an ore of uranium. Its name comes from the faint blue glow produced by the element as it decays. The property was used for many years in luminous paint for clock and watch hands and dials and also in treating some forms of cancer. However, its extreme radioactive nature means that it is rarely used today. Pierre Curie (1859 – 1906) and Marie Sklodowska Curie (1867 – 1934), c. 1903. Source: Magnus Manske, https://commons.wikimedia.org/wiki/File:Pierre_Curie_ (1859-1906)_and_Marie_Sklodowska_Curie_(1867-1934),_c._1903_ (4405627519).jpg, licensed under CC0 1.0 Universal (CC0 1.0). 358 The periodic table 11.3.1 Physical properties of Group 2 elements The elements in Group 2 are all metallic in nature with typical properties of metals, although the first member of the group, beryllium, shows some differ-ences. The metals are all silvery grey when pure, although magnesium and beryl-lium react slowly with air to become coated with a thin layer of the white metal oxide, MO, that prevents further reaction. Table 11.3 gives some physical prop-erties of the elements of Group 2. Atomic radii and ionisation energy The metallic radii of the elements increase on going down the group.

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  Inorganic Chemistry

  Butterworths Intermediate Chemistry

  • C. Chambers, A. K. Holliday(Authors)
  • 2016(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  Most solid compounds of Group I and II elements, however, have ionic structures and the properties associated with such structures — high m.p. and b.p., Chapter 6 Groups I and II Lithium, sodium, potassium, rubidium, caesium bprvnium magnesium, calcium, strontium, barium 111 The elements Table 6.1 Selected properties of the elements of Groups I and II Element Li Na K Rb Cs Be Mg Ca Sr Ba Atomic number 3 11 19 37 55 4 12 20 38 56 Outer electrons 2s 1 3s 1 4s l 5s 1 6s 1 2s 2 3s 2 4s 2 5s 2 6s 2 Density g e m -3 0.535 0.971 0.862 1.532 1.90 1.86 1.75 1.55 2.6 3.59 m.p./K 452 370.9 336.5 312 301.5 1553 924 1124 1073 998 b.p./K 1609 1155.9 1035 973 943 3243 1380 1760 1639 1910 Hardness {Brinell) 0.06 0.07 0.04 0.03 0.02 30-40 23 20 — Table 6.2 Further properties of the elements of Groups I and II Li Na K Rb Cs Be Mg Ca Sr Ba Ionization energy* k J m o P 1 520 496 419 403 376 2657 2187 1735 1613 1467 Metallic radius nm 0.152 0.186 0.227 0.248 0.263 0.112 0.160 0.197 0.215 0.221 Ionic radius nm 0.060 0.095 0.133 0.148 0.169 0.031 0.065 0.099 0.113 0.135 Heat of vaporization at 298 K k J m o P 1 152.5 108.6 90.0 85.8 78.8 326 149 177 164 178 Hydration energy ι gaseous kJ mol 519 406 322 293 264 2494 1921 1577 1443 1305 of ion -1 E^/V -3.04 -2.71 -2.92 -2.93 -2.92 -1.85 -2.37 -2.87 -2.89 -2.91 *For Li—Cs, first ionization energy; Be—Ba, sum of first and second ionization energies. solubility in water rather than in organic solvents and electrical conductance when molten. 6.1.3 Ions in solution The hydration energies (strictly, hydration enthalpies) fall, as expected, as we descend either Group, and are larger for Group II than for Group I ions. The solubilities of the salts of Groups I and II are determined by a balance between lattice energy, hydration energy and the entropy change in going from solid to solution, and only a few generalizations are possible. Thus high charge and low ionic radii tend to produce insolubility (for example salts of

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  Available until 27 Jan |Learn more

  Geochemistry

  Pathways and Processes

  • Harry Y. McSween, Steven M. 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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