Metalloid properties

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. 

In addition to this, we may change the contact potential difference by intensifying the metallic or metalloidal properties (donor or acceptor). For example, after heating lead sulfide powder in vacuo this substance acquires metallic properties on heating it in suKur vapor it becomes metalloidal [71],... 

Figure in,9 shows the change in the charge of lead sulfide particles (the normal type and those with metallic or metalloidal properties) with substrate potential. 

The communication of metalloidal properties to the powder (curves 3) leads to a rise in contact potential difference,and hence a rise in the adhesive forces and the charges observed on detachment of the particles. The communication of metallic properties to the powder (curves 2) leads to the opposite result. 

Metalloid azoles frequently show expected properties, especially if not too many heteroatoms are present. Thus Grignard reagents prepared from halogen-azoles (see Section 4.02.3.9.3) show normal reactions, as in Scheme 60. 2-Lithioimidazoles react normally, e.g. with acetaldehyde (Scheme 61) (70AHC(12)103) 5-lithioisothiazoles (see Scheme 62) (72AHC(14)1) and 2-lithiothiazoles undergo many of the expected reactions. 

Some physical properties of the elements are compared in Table 10,2. Germanium forms brittle, grey-white lustrous crystals with the diamond structure it is a metalloid with a similar electrical resistivity to Si at room temperature but with a substantially smaller band gap. Its mp, bp and associated enthalpy changes are also lower than for Si and this trend continues for Sn and Pb which are both very soft, low-melting metals. 

Two other important properties of silicon-carbon bonds are that carbonium ions fl and carbanions (or metalloid equivalents) a to silicon are favoured over alternatives, i.e. that situations involving Si—C—C+ and Si—C are thermodynamically relatively good. 

A metalloid has the appearance and some properties of a metal but behaves chemically like a nonmetal. 

Boron forms perhaps the most extraordinary structures of all the elements. It has a high ionization energy and is a metalloid that forms covalent bonds, like its diagonal neighbor silicon. However, because it has only three electrons in its valence shell and has a small atomic radius, it tends to form compounds that have incomplete octets (Section 2.11) or are electron deficient (Section 3.8). These unusual bonding characteristics lead to the remarkable properties that have made boron an essential element of modern technology and, in particular, nan otechn ol ogy. 

Boron is a hard metalloid with pronounced nonmetallic properties. Aluminum is a light, strong, amphoteric, reactive metallic element with a surface that becomes passivated when exposed to air. 

Boron, a metalloid with largely nonmetallic properties, has acidic oxides. Aluminum, its metallic neighbor, has amphoteric oxides (like its diagonal neighbor in Group 2, beryllium). The oxides of both elements are important in their own right, as sources of the elements, and as the starting point for the manufacture of other compounds. 

The elements show increasing metallic character down the group (Table 14.6). Carbon has definite nonmetallic properties it forms covalent compounds with nonmetals and ionic compounds with metals. The oxides of carbon and silicon are acidic. Germanium is a typical metalloid in that it exhibits metallic or nonmetallic properties according to the other element present in the compound. Tin and, even more so, lead have definite metallic properties. However, even though tin is classified as a metal, it is not far from the metalloids in the periodic table, and it does have some amphoteric properties. For example, tin reacts with both hot concentrated hydrochloric acid and hot alkali ... 

Germanium was the semiconductor material used in the development of the transistor in the early 1950s. However, it exhibits high junction leakage current due to its narrow bandgap and is now largely replaced by silicon. It is a brittle metalloid element with semiconductor characteristics. The properties of germanium are summarized in Table 8.3.1 lP l... 

Regardless of their possible metallic properties, metal-rich Zintl system or phases are defined here as cation-rich compounds exhibiting anionic moieties of metal or metalloid elements whose structures can be generally understood by applying the classical or modern electron counting rules for molecules. 

The elements can be divided into categories metals, nonmetals, and metalloids. Examples of each appear in Figure U. Except for hydrogen, all the elements in the left and central regions of the periodic table are metals. Metals display several characteristic properties. For example, they are good conductors of heat and electricity and usually appear shiny. Metals are malleable, meaning that they can be hammered into thin sheets, and ductile, meaning that they can be drawn into wires. Except for mercury, which is a liquid, all metals are solids at room temperature. 

Ion formation is only one pattern of chemical behavior. Many other chemical trends can be traced ultimately to valence electron configurations, but we need the description of chemical bonding that appears in Chapters 9 and 10 to explain such periodic properties. Nevertheless, we can relate important patterns in chemical behavior to the ability of some elements to form ions. One example is the subdivision of the periodic table into metals, nonmetals, and metalloids, first introduced in Chapter 1. 

C08-0086. We list polonium as a metal, but some chemists classify it as a metalloid. List other metals that might be expected to show properties in between those of metals and metalloids. 

As is typical of second-row elements, boron has properties that distinguish it from the other elements in Group 13 as well as from the rest of the metalloids. The unique features of boron chemistry can be attributed to... 

A major and growing use of the minor metalloids is in semiconductor fabrication. Germanium, like silicon, exhibits semiconductor properties. Binary compounds between elements of Groups 13 and 15 also act as semiconductors. These 13-15 compounds, such as GaAs and InSb, have the same number of valence electrons as Si or Ge. The energy gap between the valence band and the conduction band of a 13-15 semiconductor can be varied by changing the relative amounts of the two components. This allows the properties of 13-15 semiconductors to be fine-tuned. 

There are two basic types of elements metals and nonmetals. The metals, such as copper, gold, and iron (see Chapter 5), make up more than three-quarters of the total number of elements nonmetals, such as, for example, chlorine, sulfur and carbon, make up much of the rest. Other elements, however, known as the metalloids or semimetals, have properties intermediary between the metals and the nonmetals (see Appendix I). Only a few elements, such as the metals gold and copper and the nonmetal sulfur, which are known as the native elements, occur in nature uncombined. Most elements occur naturally combined with others, forming compounds. It is from these compounds, which occur in the crust of the earth as minerals, rocks, or sediments, that humans extract most of the elements that they require (Klein 2000). 

The 92 chemical elements that occur naturally in the earth can be divided into two main groups metals and nonmetals. Although the distinction between the two is not always sharp and clear, it can be said that over 70 of the 92 elements are metals among the fewer than 22 remaining non-metals, six are known as metalloids, which have properties that fall between those of metals and nonmetals (see Appendix I). 

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