Covalent compounds, 140 different

Covalent Compounds The names of covalent compounds differ from those of ionic compounds in that covalent compounds require the use of a prefix to indicate the number of atoms present. Examples are CO carbon monoxide and C02 carbon dioxide. Other prefixes that can be used are tri- and tetra-. 

How do the basic particles of ionic and covalent compounds differ ... 

The covalent compounds of graphite differ markedly from the crystal compounds. They are white or lightly colored electrical insulators, have Hi-defined formulas and occur in but one form, unlike the series typical of the crystal compounds. In the covalent compounds, the carbon network is deformed and the carbon atoms rearrange tetrahedraHy as in diamond. Often they are formed with explosive violence. 

A useful property of liquids is their ability to dissolve gases, other liquids and solids. The solutions produced may be end-products, e.g. carbonated drinks, paints, disinfectants or the process itself may serve a useful function, e.g. pickling of metals, removal of pollutant gas from air by absorption (Chapter 17), leaching of a constituent from bulk solid. Clearly a solution s properties can differ significantly from the individual constituents. Solvents are covalent compounds in which molecules are much closer together than in a gas and the intermolecular forces are therefore relatively strong. When the molecules of a covalent solute are physically and chemically similar to those of a liquid solvent the intermolecular forces of each are the same and the solute and solvent will usually mix readily with each other. The quantity of solute in solvent is often expressed as a concentration, e.g. in grams/litre. 

The systematic investigation of the chemistry of the transition elements began in the nineteenth century, and it rapidly became apparent that many of the compounds were somewhat different from those with which chemists were then familiar. There was a clear difference between the behaviour of simple ionic compounds such as sodium chloride and typical transition-element compounds such as FeCl2-4H20. It was also obvious that the compounds did not resemble the typically covalent compounds of organic chemistry. It was considered that many of the compounds formed by transition metals were of a complex constitution, and they were accordingly known as complexes. 

Change from a covalent compound to a salt by a slight difference in carbocation stability 212... 

CHANGE FROM A COVALENT COMPOUND TO A SALT BY A SLIGHT DIFFERENCE IN CARBOCATION STABILITY... 

It also turns out from the reduction potentials of [112" ], [25" ], [99 ], [100 ], [26 ] and [IIS" ] (Table 8) that the product of the reaction, a covalent compound or a salt with [2 ], changes abruptly from a covalent compound to a salt as the stability of the cation moiety is gradually increased. The borderline between the two types of reactions lies between [100" ] and [26 ]. The difference (0.017 V) in the E ed values of these cations suggests that only a slight difference (0.4 kcal mol or less) in electronic stability can completely switch the type of bond. 

Consider the differences in properties between covalent compounds and ionic compounds. Do these differences imply that covalent bonds are weaker than ionic bonds Give evidence to justify your answer. 

Solubility data are presented for practically all entries. Quantitative data are also given for some compounds at different temperatures. In general, ionic substances are soluble in water and other polar solvents while the non-polar, covalent compounds are more soluble in the non-polar solvents. In sparingly soluble, slightly soluble or practically insoluble salts, degree of solubility in water and occurrence of any precipitation process may be determined from the solubility product, Ksp, of the salt. The smaller the Ksp value, the less its solubility in water. 

It is easy to see from the examples in the previous section how two identical atoms can share electrons to achieve an octet and form diatomic molecules. Because each of our examples dealt with identical atoms, the electrons can be considered to be shared equally by each atom. The bond formed when the atoms are equally shared can be thought of as a pure covalent bond. But what happens in covalent compounds Remember, a compound contains two different elements. When atoms of two different elements are held together by covalent bonds, there is an unequal sharing of the electrons. The sharing of electrons in a covalent bond may be compared to you and a friend sharing a flashlight while walking down a dark street. If you and your friend both held the... 

The systems of valent states and oxidation states introduced by chemists are not merely electron accounting systems. They are the systems which allow us to understand and predict which ratios of elements will form compounds and also suggests what are the likely structures and properties for these compounds (3). In the case of highly covalent compounds, the actual occupancy of the parent orbitals may seem to be very different than that implied from oxidation states if ionicity were high. Nonetheless, even some physicists have recognized the fundamental validity and usefulness of the chemist s oxidation state approach where the orbitals may now be described as symmetry or Wannier orbitals (6). 

Problem 1.2 How do the boiling points, melting points, and solubilities of covalent organic compounds differ from those of salts Account for the differences. 

The tetrahedral radii for first-row and second-row elements are identical with the normal single-bond covalent radii given in Table 7-2. For the heavier atoms there are small differences, amounting to 0.03 A for bromine and 0.05 A for iodine. It is possible that these differences are due to the difference in the nature of the bond orbitals in tetrahedral and normal covalent compounds. 

Molecules are the fundamental units of the gaseous covalent compound fluorine, F2. Notice that in this model of a fluorine molecule, the spheres overlap, whereas the spheres shown earlier for ionic compounds do not. Now you know that this difference in representation is because of the difference in bond types. 

To a greater or lesser degree the spectra of all C-6 ionic salts, whether they are substituted with a covalent group at C-2 or not, are comprised of a mixture of the spectra of C-6 ionic and C-6 covalent forms. Differences among the spectra of the compounds result from secondary effects on the structure of the bare anions such as hydrogen bonding and dimerization due to hydrophobic dye/dye molecular interactions. This is particularly obvious when the fluorescence spectra of the ammonium salts at room temperature of the C-2, C-6 bis trimethylammonium salt shows a triad of broad peaks centered at 583 nm. At reduced temperature the same compound shows three sharper peaks at 538, 583, and 605 nm. The shortest wavelength of these... 

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