Each atom in the chain bonds to two other atoms. Tellurium forms crystals that contain infinite spiral chains of tellurium atoms. The structures of arsenic and antimony are similar to the structure of graphite, covered later in this chapter. The crystal structure of antimony is similar to that of arsenic, both shown in. Each arsenic atom forms covalent bonds to three other atoms within the sheet. There are several allotropes of arsenic with the most stable being layer like and containing puckered sheets of arsenic atoms. Single crystals of silicon and germanium are giant, three-dimensional molecules. Each atom within the crystal has covalent bonds to four neighboring atoms at the corners of a regular tetrahedron. Silicon and germanium crystallize with a diamond structure. In this regard, these elements resemble nonmetals in their behavior.Įlemental silicon, germanium, arsenic, antimony, and tellurium are lustrous, metallic-looking solids. Although tellurium(VI) compounds are known (for example, TeF 6), there is a marked resistance to oxidation to this maximum group oxidation state.Ĭovalent bonding is the key to the crystal structures of the metalloids. The most stable tellurium compounds are the tellurides-salts of Te 2− formed with active metals and lanthanides-and compounds with oxygen, fluorine, and chlorine, in which tellurium normally exhibits an oxidation state 2+ or 4+. Tellurium combines directly with most elements. These elements tarnish only slightly in dry air but readily oxidize when warmed. Germanium is very similar to silicon in its chemical behavior.Īrsenic and antimony generally form compounds in which an oxidation state of 3+ or 5+ is exhibited however, arsenic can form arsenides with an oxidation state of 3−. Carbon, on the other hand, has no available valence shell orbitals tetrahedral carbon compounds cannot act as Lewis acids. Silicon’s empty d orbitals and boron’s empty p orbital enable tetrahedral silicon compounds and trigonal planar boron compounds to act as Lewis acids. The major differences between the chemistry of carbon and silicon result from the relative strength of the carbon-carbon bond, carbon’s ability to form stable bonds to itself, and the presence of the empty 3 d valence-shell orbitals in silicon. Silicon has the valence shell electron configuration 3 s 23 p 2, and it commonly forms tetrahedral structures in which it is sp 3 hybridized with a formal oxidation state of 4+. Although boron exhibits an oxidation state of 3+ in most of its stable compounds, this electron deficiency provides boron with the ability to form other, sometimes fractional, oxidation states, which occur, for example, in the boron hydrides. However, boron has one distinct difference in that its 2 s 22 p 1 outer electron structure gives it one less valence electron than it has valence orbitals. All three elements form covalent compounds. The metalloid boron exhibits many similarities to its neighbor carbon and its diagonal neighbor silicon. In this section, we will briefly discuss the chemical behavior of metalloids and deal with two of these elements-boron and silicon-in more detail. This intermediate behavior is in part due to their intermediate electronegativity values. For example, the pure metalloids form covalent crystals like the nonmetals, but like the metals, they generally do not form monatomic anions. Their chemical behavior falls between that of metals and nonmetals. They are semiconductors because their electrons are more tightly bound to their nuclei than are those of metallic conductors. These elements look metallic however, they do not conduct electricity as well as metals so they are semiconductors. The metalloids are boron, silicon, germanium, arsenic, antimony, and tellurium. Describe the preparation, properties, and compounds of boron and siliconĪ series of six elements called the metalloids separate the metals from the nonmetals in the periodic table.Describe the general preparation, properties, and uses of the metalloids.By the end of this section, you will be able to:
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