Classification of elements into metals and nonmetals

The classification of elements into metals and nonmetals, with the intermediate category of semimetal, is a fundamental one in inorganic chemistry. 

The periodic table is a classification scheme for elements that is tremendously useful in learning the properties of the elements. It consists of seven periods and 16 classical groups, or families (18 in a more modem but less useful version). Several of the groups have names, which beginning students need to leam. The elements are separated into metals and nonmetals on the periodic table. They are also subdivided into main group elements, transition elements, and inner transition elements. (Section 1.5)... 

The most fundamental classification of the chemical elements is into metals and nonmetals. Metals typically have the following physical proper-fies a lustrous appearance, the ability to change shape without breaking (they can be pulled into a wire or pounded into a thin sheet), and excellent conductivity of heaf and elecfricity. Nonmetals fypically do nof have these physical properties, although there are some exceptions. (For example, solid iodine is lustrous the graphite form of carbon is an excellent conductor of elecfricity and the diamond form of carbon is an excellent conductor of heaf.) However, it is the chemical differences between metals and nonmetals that interest us the most ... 

If you were asked to place each of the problematic elements Into one of three categories, metal, semimetal, and nonmetal, where would you place them (In doing this exercise do not be surprised if you have difficulty In some cases, or if you come to different conclusions from other people. Many of the fundamental ideas of chemistry are not as exact as is often made out. We have to get used to rules that have exceptions, and classifications that produce border-line cases. This is of the character of chemistry, which in terms of exactitude of its theories, stands very much between physics on the one hand and biology on the other.)... 

Table 4-5, The Periodic Table, shows how we classify the known elements as metals (shown in blue), nomnetals (tan), and metalloids (green). The elements to the left of those touching the heavy stairstep line are metals (except hydrogen), and those to the right are nonmetals. Such a classification is somewhat arbitrary, and several elements do not fit neatly into either class. Most elements adjacent to the heavy line are often called metalloids (or semimetals), because they are metallic (or nonmetallic) only to a limited degree.

The elements from the main groups are divided next, as in the former classification, into metals (to which xenon joins also) and nonmetals, that is, again a more distinct separation than that without normalization. Finally, the transition elements are divided into two classes First, the more dense elements from the period 5 (Nb-Pd) and 6 (Hf-Au), together with Th and U, as well as the nonmetallic refractory elements from the main groups (B, C, Si) and, second, the early transition elements and the lanthanides, together with Ge. In this way, the classification is more like that given by chemical intuition but less detailed we may say that by normalization a loss of information arises. 

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. 

Simply stated, inorganic chemistry deals with the 117 elements in the periodic table other than carbon. The elements in the periodic table are broadly grouped into three classifications metals, nonmetals, and metalloids (or semimetals). Inorganic chemists describe the physical and chemical properties of the elements themselves, as well as all of the chemical compounds the elements can form, both in nature and in the laboratory. 

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