Group 2 Reactivity

6 Key excerpts on "Group 2 Reactivity"

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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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  Concise Chemistry of the Elements

  • S C Siekierski, J Burgess(Authors)
  • 2002(Publication Date)
  • Woodhead Publishing

    (Publisher)

  This results in high chemical reactivity, particularly with respect to electronegative elements, including reaction of Be and Mg with the strongly bonded N 2 molecule. Because of relatively low ionization potentials and high salvation enthalpies of the M 2 + ions, the elements from magnesium to barium, like the alkali metals, dissolve in liquid ammonia. Since the Group 2 elements are, except for beryllium, highly electropositive they form ionic compounds with most elements, in which they exhibit the oxidation number +2. A large covalency contribution is observed in most beryllium compounds and in organomagnesium compounds, such as MgR 2 and RMgX (Grignard reagents). Because of their large radii, organometallic compounds of Ca, Sr and Ba are highly ionic and reactive. As is the case with alkali metal hydrides the Group 2 hydrides MH 2 contain the Ir anion, except for BeH 2 and MgH 2 where there is a high contribution from covalency to the bonding. The Group 2 elements do not show the +I oxidation state. This is

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  eBook - ePub

  Soil Chemistry

  • Daniel G. Strawn, Hinrich L. Bohn, George A. O'Connor(Authors)
  • 2019(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  2 PROPERTIES OF ELEMENTS AND MOLECULES

  2.1 Introduction

  More than 150 years ago, Dmitri Mendeleev arranged the elements according to their properties, and introduced the concept of the periodic table (

  Figure 2.1

  ). The elements are grouped as columns in the periodic table based on occupancy of their outer electron shells. They are further categorized into groups based on whether they are metallic, non‐metallic, gas, or inert. Another categorization defines the elements as alkali elements, alkaline earth elements, transition metals, post‐transition metals, metalloids, nonmetals, halogens, noble gases, rare earth elements (REE), actinides, and lanthanides. Rare earth elements are lanthanide elements plus scandium and yttrium. Despite their name, REE are quite common in soils and rocks in low concentrations; they are so named because they do not commonly occur in easily recovered ore‐rich bodies. Elements that are within a group (column) often have similar properties, such as oxidation state (ion form) and reactivity. For example, Group 1 elements, the alkali metals lithium to francium, are all monovalent cations. In addition, element atomic size and mass increases from top row down: Li < Na < K < Rb < Cs < Fr.

  The fundamental properties of elements and importance of these properties for understanding and predicting chemical processes are listed in

  Table 2.1

  . Some of the most important chemical properties in soils that control reactivity, availability, and speciation of chemicals are oxidation state, ionic radius, and type of bonds that occur within chemicals and in soil solids.

  This chapter presents fundamental properties of atoms and molecules. The ionic and bonding properties discussed are key concepts used to understand how chemicals react in the environment. For example, the fundamental properties of elements explain ion exchange, activity of ions in soil solution, bonding of ions within minerals and organic matter, soil mineralogy, and organic chemical reactivity. The fundamental chemical concepts presented in this chapter are used throughout this text to understand reactivity of chemicals in soils.

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  Inorganic Chemistry

  Butterworths Intermediate Chemistry

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

    (Publisher)

  110 6.1 The elements 6.1.1 General characteristics These elements form two groups, often called the alkali (Group I) and alkaline earth (Group II) metals. Some of the physical properties usually associated with metals — hardness, high m.p. and b.p. — are noticeably lacking in these metals, but they all have a metallic appearance and are good electrical conductors. Table 6.1 gives some of the physical properties. From Table 6.1, it is easy to see that Group II metals are more dense, are harder and have higher m.p. and b.p. than the corresponding Group I metals. In Chapter 2, a discussion of the theory of metallic bonding indicated that the strength of such bonding generally depends on the ratio (number of electrons available for bonding)/(atomic radius). The greater this ratio is, the stronger are the bonds between the metal atoms. In the pre-transition metals, this ratio is small and at a minimum in Group I with only one bonding electron. Metallic bond strength is greater in Group II but there are still only two bonding electrons available, hence the metals are still relatively soft and have low melting and boiling points. Hardness, m.p. and b.p. all decrease steadily down Group I, the metallic bond strength decreasing with increasing atomic radius. These changes are not so well marked in Group II but note that beryllium and, to a lesser extent, magnesium are hard metals, as a result of their small atomic size; this property, when coupled with their low density, makes them of some technological importance (p. 113). A full discussion of the changes in ionization energy with group and period position has been given in Chapter 2. These data are given again in Table 6.2. 6.1.2 Formation of ions We note first that the elements are all electropositive, having relatively low ionization energies, and are, in consequence, very reactive.

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  Trace Elements in Soils and Plants

  • Alina Kabata-Pendias(Author)
  • 2010(Publication Date)
  • CRC Press

    (Publisher)

  135 7 Elements of Group 2 (Previously Group IIa) The trace elements of Group 2, beryllium (Be), strontium (Sr), and barium (Ba), belong to the alkaline earths and behave similarly to Ca and Mg. Their physical properties, especially sizes of their ionic radii are fairly similar to those of Ca, and they may substitute for each other, however, the small ionic radius of Be prevents its replacement by other cations (Table 7.1). A characteristic of these cations is the small ionic radius and high charge to radius ratio. All the alkaline earths are associated with the carbon cycle that strongly controls their behavior in the environment. Be in the terrestrial environment is more susceptible to hydrolysis and complexation processes than other elements of this group. Radionuclides of this group, and especially 90 Sr and 226 Ra, could present significant risk of environmental hazard. Radium (Ra), which occurs as several radionuclides, is a product after the decay chain of U and Th. BERYLLIUM I I NTRODUCTION A The abundance of Be in the Earth’s upper crust averages 3 mg/kg, but the range of 4–6 mg/kg has been cited quite frequently (Figure 3.2). Be is the lightest of the alkaline earths and although widely distributed, exists in relatively small quantities and is likely to concentrate in acid igneous rocks and in argillaceous sediments, where its contents reach up to 6 mg/kg, (Table 7.2). However, some alkaline rocks tend to be enriched in this element. Organic matter reveal a sorption capacity for Be, and thus its concentrations in coal vary broadly from 11 to 330 mg/kg and average 2.5 mg/kg (Finkelman, 1999; Llorens et al., 2000). However, higher contents of Be, from 100 to 1000 mg/kg, have also been reported, and the highest Be concentration, up to 2000 mg/kg, was found in coals from the North Bohemian Basin in the Czech Republic (Veselý et al., 2002). Crude oil may content from 0.0005 to 0.5 mg Be/kg, depending upon local geochemical conditions.

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  Chemistry All-in-One For Dummies (+ Chapter Quizzes Online)

  • Christopher R. Hren, John T. Moore, Peter J. Mikulecky(Authors)
  • 2022(Publication Date)
  • For Dummies

    (Publisher)

  FIGURE 5-2: Groups on the periodic table.
• The VIIA family is made up of the halogens . They all tend to gain a single electron in reactions. Important members in the family include chlorine (Cl), used in making table salt and bleach, and iodine (I). Tincture of iodine is sometimes used as a disinfectant.
• The VIIIA family is made up of the noble gases. These elements are very unreactive. For a long time, the noble gases were called the inert gases, because people thought that these elements wouldn’t react at all. Later, a scientist named Neil Bartlett showed that at least some of the inert gases could be reacted, but they required very special conditions. Since Bartlett’s discovery, the gases have been referred to as noble gases.
Q. What group, using the Roman numeral numbering system and the numerical system, is calcium located within?
A. Calcium is located in group IIA. This group is also called group 2. The groups are the vertical columns found across the periodic table. They are numbered with a Roman numeral system IA through VIIIA, or a numerical system, 1–18.
Q. What period is bromine located in?
A. Bromine is located in period 4. Remember, periods are the rows down the periodic table. They are numbered 1–7 as you go down the table.
1 What group, using the Roman numeral numbering system, are the following elements in?
1. sodium
2. gallium
3. strontium
4. oxygen
5. xenon
2 What period are the following elements in?
1. magnesium
2. hydrogen
3. francium
4. titanium
5. selenium

Meeting the metals, nonmetals, and metalloids

In addition to the groups (families) you see in Figure 5-2 , there are other ways to classify elements on the periodic table. The most common way is to arrange elements based on their metallic properties. Most of the elements on the periodic table are considered metals. The metals have properties that you normally associate with the metals you encounter in everyday life. They are solid (with the exception of mercury, Hg, a liquid), shiny, good conductors of electricity and heat, ductile (they can be drawn into thin wires), and malleable (they can be easily hammered into very thin sheets). The large block of metals that is not part of the alkali or alkaline earth metals is called the transition metal block. Transition metals have properties that vary from extremely metallic, on the left side, to far less metallic, on the right side. Figure 5-3