Carbides ionic

The acetylide ion, C22-, is isoelectronic with N2, CO, and CN- (see Chapter 2), and it is presumed to be present in calcium carbide, CaC2. Thus, a reaction producing acetylene from calcium carbide can be shown as 

Acetylides can be produced in some cases by the direct reaction of carbon with a metal or metal oxide. For example, 

Other carbides (e.g., Be2C and ALtC3) behave as if they contain C4- and react with water to produce CH4  

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Carbon forms ionic carbides with the metals of Groups 1 and 2, covalent carbides with nonmetals, and interstitial carbides with d-block metals. Silicon compounds are more reactive than carbon compounds. They can act as Lewis acids. 

Ion exclusion chromatography, of ascorbic acid, 25 760 Ion hopping, 14 469 Ionic aggregates, 14 463—466 Ionically conducting polymers, 13 540 Ionic carbides, 4 647 Ionic compounds, rubidium, 21 822 Ionic conduction, ceramics, 5 587-589 Ionic crystals, 19 185. See also Silver halide crystals... 

Give an example of an ionic carbide. What is the oxidation state of carbon in this substance ... 

Group 2 elements typically form ionic carbides of formnla MC2. When BeO is heated with C at 1900-2000 °C, a brick red colored carbide of formula Bo2C results. This ionic compound adopts the antifluorite structure, that is, like the Cap2 structure except that the positions of the cations and Anions are interchanged. It is unusual because it reacts with water, forming methane, and is thus called a methanide (equation 9). 

The C NMR spectra of the ionic carbides CaC2 and BaC2 have been determined by Wrackmeyer et al. (1990) who report 8iso values of 206.2 ppm for CaC2 and 232.1 ppm for BaC2, both shifts with respect to TMS. The NMR results indicate that the environment of the carbon atoms in these compounds is not axially symmetric, and that the carbide unit in these ionic carbides is not comparable with the carbon-carbon triple bond in alkynes. 

Ionic carbides Metallic carbides. Metalloid carbides... 

Refractory metal carbides (TaC, WC, M02C) and some covalent carbides (SiC, B4C) have a positive effect on diamond nucleation, while effects of ionic carbides (AI4C3, liquid salts, etc.) are still less known.l ... 

The alkali metals form only ionic carbides, mostly simple ionic salts of acetylene, M2C2, which liberate acetylene on reaction with moisture. There has been much recent interest in permetalated and hypermetalated hydrocarbon species, or methanides . Most studied in this respect has been lithium, presumably because of its volatility and amenability to calculation. Mass spectrometric and calculational evidence has been presented for CLie, CLis, and C2Li4, but real samples of CLi4, C3Li4, and C5Li4 are preparable. All are pyrophoric powders. The heavier metals form another class of carbide , the graphite intercalation compounds, but as the electron has not been totally freed from the metal, these were considered in the previous section. 

Ionic carbides, which contain the carbide ion C" . An example is aluminum carbide, AI4C3. Compounds of this type react with water to give methane (they were formerly also called methanides). The dicarbides are ionic carbon compounds that contain the dicarbide ion C C". The best-known example is calcium dicarbide, CaC2, also known as calcium carbide, or simply carbide. Compounds of this type give ethyne with water. They were formerly called acetylides or ethynides. Ionic carbides are formed with very electropositive metals. They are crystalline. 

Ni3C) have properties intermediate be-tw een those of interstitial and ionic carbides. 

The binary compounds of carbon with metals, metalloids, and certain nonmetals are called carbides. The more active metals form ionic carbides, and the most common of these contain the acetylide ion (C2 ). This ion is isoelectronic with N2, and its Lewis structure, [ C=C ], has a carbon-carbon triple bond. The most important ionic carbide is calcium carbide (CaC2), produced by the reduction of CaO with carbon at high temperature ... 

Interstitial carbides, which are INTERSTITIAL COMPOUNDS of carbon with transition metals. Titanium carbide (TiC) is an example. These compounds are all hard solids with high melting points and metallic properties. Some carbides (e.g. nickel carbide M3C) have properties intermediate between those of interstitial and ionic carbides. 

Morris, D.R. (1982) Ionic Carbides, in D.G. Lovering ed. Molten Salt Technology, Plenum Press, New-York-London, p.p. 153-183. 

The bond models for the boron-rich borides such as MBe have a common feature with the ionic carbides discussed in Section 6.4.2, in that a mechanism exists for a favorable transfer of electrons from the metal atoms to the boron framework to add a considerable ionic character to the overall bond character. Molecular orbital calculations for isolated units such as Bg, using 2s and 2p boron orbitals, reveal that the molecular orbitals can be divided into two sets one group Of six outward pointing at an energy... 

Intrinsic Stacking fault energy in silicon, 249 Inverse spinels, 285 Ion beam cleaning, 126 effect on hardness, 126-127 Ion implantation, 126-127 in AI2O3, 262-263 Ionic carbides, 294-296 Ionic ceramics, 209 Indium phosphide (InP), hardness, 83 anisotropy, 77... 

The ionic carbides, containing either the Cf or C" anions, are often prepared by the reaction of either the elements themselves or a metal oxide with carbon in an electric furnace at elevated temperatures. They can be hydrolyzed to produce various hydrocarbons in industrial processes. For example, calcium carbide, CaC2, is a major source of acetylene (briefly discussed on p. 372) as shown in Equation (15.14), and aluminum carbide, as shown in Equation (15.15), generates methane ... 

Ionic Carbides Compounds composed of carbon and a low-electronegativity metal such as an alkali metal or an alkaline earth metal are ionic carbides. Most ionic carbides contain the dicarbide ion, C2, cotmnonly called the acetylide ion. For example, calcium carbide has the formula CaC2 and a structure similar to that of NaCl (Figure 22.18 ). Calcium carbide forms by the reaction of calcium oxide with coke in an electric furnace. 

Ionic carbides react with water, forming acetylene. For example, sodium carbide reacts with water according to the reaction shown here ... 

Descaibe the difference between an ionic carbide and a covalent carbide. Which types of atoms will form these carbides with carbon ... 

Ionic carbides are composed of carbon, generally in the form of the carbide ion, 2 , and low-electronegativity metals, such as the alkali and alkaline earth metals. Covalent carbides are composed of carbon and low-electronegativity nonmetals or metalloids, such as silicon. 

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