Metalloid metallic properties

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 ... 

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. 

Elements bordering the stair-stepped line (B, Si, Ge, As, Sb, Te) are classified as metalloids. Metalloids have properties of both metals and nonmetals. Their unusual electrical properties make them valuable in the semiconductor and computer industry. 

Some of the metalloids are considered semiconductors. The term metalloids is used in this reference book because these elements do have characteristics of both metals and non-metals, and the term semiconductor refers only to particular elements somewhere between metals and nonmetals. Semiconductors also have properties of both metals and nonmetals. Therefore, they have the ability to act as conductors of electricity and thermal energy (heat), as well as the ability to act as insulators or nonconductors of electricity and heat, depending upon the kind and amount of impurities their crystals contain. Again, following the zigzag steps on the periodic table, the metalloids having properties of both metals and nonmetals are as follows boron, silicon, germanium, arsenic, antimony, tellurium, and polonium. 

Apart from the atomic noble gases, elemental substances may be classified as metallic or covalent, according to their structures and properties at room temperature and ambient pressure. Covalent elemental substances may be subdivided as molecular or non-molecular, the latter category including one-, two- or three-dimensional structures. There is a grey area between the extremes of the three-dimensional covalent structure and the typical metal semi-metallic or metalloid behaviour is found in a number of cases. Even iodine, prima facie a molecular solid, has incipient metallic properties. In this section, we explore this grey area and consider the factors that determine which type... 

The modern periodic table provides us with volumes of information about the elements. Metals are on the left side of the table, nonmetals are on the right side, and metalloids divide these two groups. In general, metals are shiny, malleable, ductile, and conduct electricity. Nonmetals are dull, brittle, and do not conduct electricity (many nonmetals are gases at room temperature). Metalloids have properties of both metals and nonmetals. 

When we classify the elements as metals and nonmetals we see that metals occupy very big part (about 80%) of the periodic table. The elements in B groups (transition elements, actinides and lanthanides) and the elements in the groups, 1 A, 2A and 3A (except hydrogen and boron) are metals. Only the eleven elements H, C, N, O, R S, Se, F, Cl, Br and I are nonmetals and the elements in group 8A are noble gases. However, among these elements, B, Si, Ge, As, Sb, Te, Po and At are metalloids and Sn, Pb and Bi and Be have metallic properties. 

Some elemental metals and many intermetallic compounds are brittle, not malleable or ductile. Borderline substances, showing metallic properties to a decreased extent, are called metalloids or semiconductors. Probably the best criterion for distinguishing a meted and a metalloid or semiconductor is the temperature coefficient of thermal and electrical conductivity. With increase in temperature, the thermal and electrical conductivity of a metal decreases, whereas that of a metalloid or semiconductor increases. 

The metallic properties are most pronounced for elements in the lower left-hand corner of the periodic table, and the non-metallic properties are most pronounced for elements in the upper right-hand corner. The transition from metals to non-metals is marked by the elements with intermediate properties, which occupy a diagonal region extending from a point near the upper center to the lower right-hand corner. These elements, which are called metalloids, include boron, silicon, germanium, arsenic, antimony, tellurium, and polonium.. 

Classifying the elements There are three main classifications for the elements—metals, nonmetals, and metalloids. Metals are elements that are generally shiny when smooth and clean, solid at room temperature, and good conductors of heat and electricity. Most metals also are malleable and ductile, meaning that they can be pounded into thin sheets and drawn into wires, respectively. Figure 6-6 shows several applications that make use of the physical properties of metals. 

Based on the trends discussed in Chapter 6, the metallic properties of the elements in group 4A should increase as the atomic number increases. Carbon is a nonmetal silicon and germanium are metalloids tin and lead are metals. With such a wide range of properties, there are few rules that apply to all members of the group. One general trend does apply. The period-2 element, carbon, is not representative of the other elements within the group. 

The trend in metallic properties is obvious as you go from the top of Group 15 to the bottom—from nitrogen (N) to phosphorus (P) to arsenic (As) to antimony (Sb) and bismuth (Bi). Nitrogen and phosphorus are nonmetals. They form covalent bonds to complete their outer-level configuration. Arsenic and antimony are metalloids and either gain or share electrons to complete their octets. Bismuth is more metallic and often loses electrons. 

The elements can be divided into three categories—metals, nonmetals, and metalloids. A metal is a good conductor of heat and electricity while a nonmetal is usually a poor conductor of heat and electricity. A metalloid has properties that are intermediate between those of metals and nonmetals. Figure 2.8 shows that the majority of known elements are metals only seventeen elements are nonmetals, and eight elements are metalloids. From left to right across any period, the physical and chemical properties of the elements change gradually from metallic to nonmetallic. 

A small group of elements, called metalloids, have properties characteristic of both metals and nonmetals. The metalloids boron, silicon, germanium, and arsenic are semiconducting elements (see Section 20.3). 

Group A elements are called representative elements Group B elements are transition elements. A bold zigzag line runs from top to bottom of the table, beginning to the left of boron (B) and ending between polonium (Po) and astatine (At). This line acts as the boundary between metals to the left and nonmetals to the right. Elements straddling the boundary, metalloids, have properties intermediate between those of metals and nonmetals. 

The heavy black line in Fig. 20.1 separates the metals from the nonmetals, except for one case. Flydrogen, which appears on the metal side, is a nonmetal. Some elementsjust on either side of this line, such as silicon and germanium, exhibit both metallic and non-metallic properties. These elements are often called metalloids, or semimetals. The fundamental chemical difference between metals and nonmetals is that metals tend to lose their valence electrons to form cations, which usually have the valence electron configuration of the noble gas from the preceding period. On the other hand, nonmetals tend to gain electrons to form anions that exhibit the electron configuration of the noble gas in... 

The group shows the normal property of a trend towards metallic character as it is descended. Selenium, tellurium and polonium have metallic allotropes and polonium has generally metalloid-type properties where they have been studied (Po is very rare). All the elements combine with a large number of other elements, both metallic and non-metallic, but in contrast to compounds of the halogens they are more generally insoluble in water, and even where soluble they do not ionize readily. 

There is, in fact, no clear-cut distinction between metals and non-metals. In the periodic table, there is a change from metallic to non-metallic properties across the table, and an increase in metalUc properties down a group. Consequently there is a diagonal around the center of the table (B, Si, As, Te) in which there is a borderline between metals and non-metals, and the metalloids are the borderline cases. Elements such as arsenic, germanium, and tellurium are semiconductors, but other elements are often said to be metalloids according to their chemical properties. Tin, for instance, forms salts with acids but also forms stan-nates with alkalis. Its oxide is amphoteric. Note also that tin has metallic (white tin) and non-metallic (gray tin) allotropes. 

Brazil nut is one of the very few naturally occurring sources of exceptionally high level of selenium [44]. Chemically, selenium is a metalloid with properties of both metals and nomnetals. It has a... 

Metalloids have properties in between metals and nonmetals. They can be found in Groups 13-16, but do not occupy the entire group. They are arranged in stair steps across the groups. 

We learn that the physical and chemical properties of metals are different from those of nonmetals. These properties arise from the fundamental characteristics of atoms, particularly ionization energy. Metalloids display properties that are intermediate between those of metals and those of nonmetals. 

Metalloids have properties intermediate between those of metals and those of nonmetals. They may have some characteristic metallic properties but lack others. For example, the metalloid silicon looks like a metal ( FIGURE 7.18), but it is brittle rather than malleable and does not conduct heat or electricity nearly as well as metals do. Compounds of metalloids can have characteristics of the compounds of metals or nonmetals. 

Nonmetals lack metallic luster and are generally poor conductors of heat and electricity. Several are gases at room temperature. Compounds composed entirely of nonmetals are generally molecular. Nonmetals usually form anions in their reactions with metals. Nonmetal oxides are acidic they react with bases to form salts and water. Metalloids have properties that are intermediate between those of metals and nonmetals. 

Arsenic is an element with the symbol As and the atomic number 33. It can occur as a pure element but is most often found in minerals containing sulfur and metals. Arsenic can exist in different structural forms (allotropes). However, gray arsenic is the most common. It is a metalloid that is brittle and a bit shiny. See Fig. 5 [25]. This form has metallic properties and has been used in industry to strengthen alloys of copper and lead. Arsenic is also a common n-type dopant in semiconductor electronic devices (example gallium arsenide is a semiconductor). Over the years arsenic and its compounds were used in the production of products like pesticides, insecticides, and treated wood items. However, because of its toxicity and harmful effects to humans, arsenic s applications have decreased. 

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