Metalloids electronegativity

Figure 3.10 The Pauling electronegativities of common elements. The color codes are green (metals), blue (nonmetals), and gray (metalloids). Electronegativities for the noble gases for which no (or very few) known compounds exist (He, Ar, Ne, Rd) are generally not assigned.

Hydrogen is unusual because it can form both a cation (1I+) and ail anion (11 ). Moreover, its intermediate electronegativity (2.2 on the Pauling scale) means that it can also form covalent bonds with all the nonmetals and metalloids. Because hydrogen forms compounds with so many elements (Table 14.2 also see Section 14.2), we shall meet more of its compounds when we study the other elements. 

In the above discussion the effect of difference in electronegativity of unlike atoms on bond length (usually a decrease) has been ignored. There is the possibility also of a small change in bond length between unlike atoms, such as of a metal and a metalloid, that reflects the difference in the nature of the overlapping orbitals, in addition to the effects of partial ionic character and of electron transfer. I believe that a thorough... 

Diagonal similarities refer to chemical similarities of Period 2 elements of a certain group to Period 3 elements, one group to the right. This effect is particularly evident toward the left side of the periodic table. One example is the pair, B and Si, which are both metalloids with similar properties. Another example is the pair, Li and Mg. They have similar ionic charge densities and electronegativities their compounds are similar in... 

Symbol Sb atomic number 51 atomic weight 121.75 Group VA (group 15) element atomic radius 1.41A ionic radius 86 + 0.76A covalent radius 1.21A electronic configuration [Kr] 4di°5s25p3 a metalloid element electronegativity 1.82 (Allred-Rochow type) valence states +5, +3, 0 and -3 isotopes and natural abundance Sb-121 (57.3%), Sb-123 (42.7%)... 

Symbol As atomic number 33 atomic weight 74.922 covalent radius AsS+ 1.2 lA electron configuration [Ar] 4s23di°4p3 a Group VA (Group 15) metalloid element electronegativity 2.20 (Allred-Rochow type) principal valence states, -1-5, +3, 0, and -3 stable isotope As-75. 

Different metal chlorides unite with one another to form double lasts. Just as the acidic and basic oxides unite together to form oxy-salts, so do the halides of an electropositive element (or radicle) unite with a halide of a less positive element (heavy metal or metalloid) to form double halides. So far as is known the alkali chlorides do not unite with one another to form double salts, nor do the halides of the same natural group form compounds with one another, but compounds of the alkali chlorides with the chlorides of the more electronegative chlorides are known. A comparison of nearly 500 double halides has been made by H. L. Wells (1901).1 He calls the one component—e.g. the alkali halide—the positive halide, and the other the negative halide. A. Werner calls the halide which plays the role of the basic oxide, the basic halide, and the other, the acid halide. A great many of the simple types of the double salts predominate. Writing the number of molecules of the positive halide first, and the negative halide second, salts of the 2 1 and 1 1 ratios cover about 70 per cent, of the list of known double halides, and 4 1, 3 1, 3 2, 2 3, and 1 2 represent over 25 per cent. Two halides sometimes unite in several proportions—for instance, six caesium mercuric halides have been reported where... 

Arsenic is a metalloid. Solid samples of elemental arsenic (As(0)) tend to be brittle, nonductile, and insoluble in water. These properties largely result from arsenic atoms forming strong covalent bonds with each other. Table 2.3 lists the common chemical and physical properties of arsenic, including its density, electronegativity, and first ionization potential. 

Although the general term carbide applies to the binary compounds of the element carbon, this term is used in systematic nomenclature only when carbon is the more electronegative of the two elements involved. Thus, C02 is called carbon dioxide and not oxygen carbide since oxygen is more electronegative than carbon. Although carbon forms binary compounds with most of the nonmetals, metalloids, and metals, only a few of the more common members of this class are considered here. 

A major group of organometallic compounds has carbon-metal covalent single bonds in which both the C and metal (or metalloid) atoms contribute one electron each to be shared in the bond (in contrast to ionic bonds, in which electrons are transferred between atoms). The bonds produced by this sharing arrangement are sigma-covalent bonds, in which the electron density is concentrated between the two nuclei. Since in all cases the more electronegative atom in this bond is carbon... 

From the electronegativities shown in Figs. 2.4.2 and 2.4.3, it is seen that metals are less electronegative, with xs < 2, nonmetals are more electronegative, with xs > 2. Around xs 2, we have metalloid elements such as B, Si Ge, Sb, and Bi. Most of these elements have semi-conducting properties. For elements of the same group, xs decreases as we go down the Periodic Table. However, because of relativistic effects, for transition metals from group 7 to... 

The electronegativity of C is 2.54, as compared with 1.92 for Si. Carbon is strictly nonmetallic whereas Si is essentially a non-metallic element with some metalloid properties. 

Compounds of boron and the less electronegative elements (metals and metalloids) are loosely referred to as borides, a very large class encompassing hundreds of known compounds. Well-characterized binary transition metal borides number over 120, and include compounds of all of the d-block elements except Zn, Ag, Cd, Au, and Hg (Cr alone forms nine known borides). 

The scale extends horn cesium, with electronegativity 0.7, to fluorine, with electronegativity 4,0. Fluorine is by tar the most electronegative element, with oxygen in second place, and nittogen and chlorine in third place. Hydrogen and the metalloids are in the center of the scale, with electronegativity values close to 2. The metals have values of about 1.6 or less. 

The shaded elements are metalloids, based on their electronegativities. 

Figure 6.12. A separation of metal ions and metalloid ions [As(III) and Sb(IU)] into three categories class A, borderline, and class B. The class B index is plotted for each ion against the class A index 2 /r. In these expressions, X is the metal-ion electronegativity, r its ionic radius, and Z its formal charge. (Adapted from Nieboer and Richardson, 1980.)...

Semi-metallic behavior is not confined to the elements, but is also found in alloys and compounds. When involved in chemical bonding, the metalloids again exhibit intermediate qualities. They are capable of taking electrons from most metals and will readily lose electrons to most nonmetals. Their electronegativity values are also mid-range. Consequently, it is unlikely for them to be involved in ionic bonding when found in compounds, they will usually establish covalent bonding. 

The elements considered so far lie on the border between covalent and molecular solids. Other elements, those of intermediate electronegativity, exist as solids on the border between metallic and covalent these are called metalloids. Antimony has a metallic Inster, for example, bnt is a rather poor condnctor of electricity and heat. Silicon and germaninm are semiconductors, with electrical condnctivities far lower than those of metals bnt still significantly higher than those of trne insulators such as diamond. Section 22.7 examines the special properties of these materials more closely. 

Each Group VIA element is less electronegative than its neighboring halogen. Oxygen and sulfur are clearly nonmetallic, but selenium is less so. Tellurium is usually classified as a metalloid and forms metal-like crystals. Its chemistry is mostly that of a nonmetal. Polonium is a metal. All 29 isotopes of polonium are radioactive. 

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