![]() Due to this free electron graphite is electric conductor while diamond is not. The three cavalent bonds form hexagonal layers and fourth unhybridised p – electron of each carbon forms an extended delocalized π - bonding with carbon atoms of adjacent layers. In diamond carbon is sp3 hybridised and has four tetrahedral bonds with adjacent carbon atoms. Allotropy is the existence of an element in two or more forms, which are significantly different in physical properties but have similar chemical properties. Example: carbon has two important allotropic forms i.e. On going down the group, tendency of catenation decreases.ĭue to high tendency of catenation carbon forms bonds with other carbon atoms and forms so many compounds which are studied in organic chemistry.Ī characteristic property of the elements of carbon family is that these show allotropy. This property of forming chains and rings is knows as catenation. These are Pb – 206, Pb – 207 and Pb – 208.Ī remarkable property of carbon is its ability to form compounds in which carbon atoms are linked to one another in chains or rings. Various isotopes of lead come at the end of the natural decay series of elements like uranium, thorium and actinium. Lead has a blue – white colour when first cut but quickly dulls on exposure to air forming Pb2O. In pure form it is too soft to be used for much else. Its chief use today is in lead – acid storage batteries such as those used in automobiles. Although lead is not very common in earth’s crust, what is there is readily available and easy to refine. Its symbol came from ‘plumber’ word because since old plumbing was done with lead pipes. It has been used for many years in the coating of steel cans for food because it is more resistant to corrosion than iron. It has the look of freshly cut aluminium but the feel of lead. The metal is silvery white and very soft when pure. It was named after the Etruscan god Tinia, the chemical symbols for it is taken from Latin Stannum. It is one of the major elements along with copper used in bronze. It is generally extracted from the by products of zinc – refining. It was also predicted by Mendeleev in 1871 (ekasilicon) to fill out his periodic table and was discovered is 1886 Winkler. Like silicon, germanium is used in the manufacture of semi – conductor devices. In another allotropic form silicon is a brown amorphous powder most familiar in “dirty” beach sand. One of its forms is shiny, grey and very brittle. Silicon is a crystalline semi – metal or metalloid. The most common compound of silicon, SiO 2 is the most abundant chemical compound in the earth’s crust. The element is on second position in abundance in the earth’s crust after oxygen, was discovered by Berzelius in 1824. The zinc blende structure is converted to a rock salt structure above 77 kbar, which in turn forms a β-tin structure above 170 kbar.The silicon name is taken from Latin silver which means “flint”. Indium arsenide (InAs) undergoes two-phase transformations. An orthorhombic structure is proposed for the high-pressure form of InP (>133 kbar). Thus, AlP undergoes a zinc blende to rock salt transformation at high pressure above 170 kbar, while AlSb and GaAs form orthorhombic distorted rock salt structures above 77 and 172 kbar, respectively. however, in each case where a high-pressure phase is observed the coordination number of both the group III and group V element increases from four to six. Not all of the III-V compounds have well characterized high-pressure phases. A very important ternary alloy, especially in optoelectronic applications, is Al x-Ga 1-x-As and its lattice parameter ( a) is directly related to the composition (x). While quaternary alloys of the type III x-III 1-x-V y-V 1-y allow for the growth of materials with similar lattice parameters, but a broad range of band gaps. ![]() ![]() Two classes of ternary alloys are formed: III x-III 1-x-V (e.g., Al x-Ga 1-x-As) and III-V 1-x-V x (e.g., Ga-As 1-x-P x). The homogeneity of structures of alloys for a wide range of solid solutions to be formed between III-V compounds in almost any combination. ![]() \) Temperature dependence of the lattice parameter for stoichiometric GaAs and crystals with either Ga or As excess. ![]()
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