Molecular compounds, concept

Color from Transition-Metal Compounds and Impurities. The energy levels of the excited states of the unpaked electrons of transition-metal ions in crystals are controlled by the field of the surrounding cations or cationic groups. Erom a purely ionic point of view, this is explained by the electrostatic interactions of crystal field theory ligand field theory is a more advanced approach also incorporating molecular orbital concepts. 

Thermochemistry of cluster compounds. In this short summary of cluster structures and their bonding, a few remarks on their thermochemical behaviour are given, in view of a possible relationship with the intermetallic alloy properties. To this end we remember that for molecular compounds, as for several organic compounds, concepts such as bond energies and their relation to atomization energies and thermodynamic formation functions play an important role in the description of these compounds and their properties. A classical example is given by some binary hydrocarbon compounds. 

Electronegativity is an important concept because the attractive force created by the positive nuclei of atoms makes it possible for both the ionic and covalent bonding of atoms to form molecular compounds. 

Chemists may distinguish between the molar masses of pure elements, molecular compounds, and ionic compounds by referring to them as the gram atomic mass, gram molecular mass, and gram formula mass, respectively. Don t be fooled The basic concept behind each term is the same molar mass. 

The following sections describe five types of reactions that you d do well to recognize (notice how their names tell you what happens in each reaction). By recognizing the patterns of these five types of reactions, you can often predict reaction products when given only a set of reactants. (Note Figuring out the formulas of products often requires you to apply knowledge about how ionic and molecular compounds are put together. To review these concepts, see Chapters 5 and 6.)... 

A molecular compound is formed by the union of two or more already saturated molecules apparently in defiance of the ordinary rules of valence. The class includes double salts, sails with water of crystallization, and metal ammonium derivatives. These salts are usually formed by Van der Waals attraction between (he constituent molecules. They do nol differ in any characteristic manner from compounds formed in strict accordance with the concept of valence They are also called addition compounds. 

KEY CONCEPT PROBLEM 2.13 Which of the following drawings is most likely to represent an ionic compound, and which a molecular compound Explain. 

This chapter has presented an overview of several important aspects of the chemistry of coordination compounds. In addition to the elementary ideas related to bonding presented here, there is an extensive application of molecular orbital concepts to coordination chemistry. However, most aspects of the chemistry of coordination compounds treated in this book do not require this approach, so it is left to more advanced texts. The references at the end of this chapter should be consulted for more details on bonding in complexes. 

Solid supports allow an easy realization of parallel synthesis. It requires just the compartmentalization of solid phase and the individualized delivery of reactants. This concept of compartmentalization was later pushed to its limit by the realization that each particle of solid support can serve as an individual compartment in which individual peptides can be produced to create libraries of millions of peptides or any other molecular species (10). This one-bead-one-compound concept is covered in detail elsewhere (10,11) and will not be discussed here in detail. 

Although the terms molecular mass and formula mass are different, and they really do represent different concepts, the method for calculating each is identical. In fact, you might not even know if the particular compound that you are calculating the mass for is molecular or ionic, but you can still get the correct value. Don t get thrown off by the language in the questions that you are asked to answer. If the question asks for the molecular mass, that is simply an indication that you are working with a molecular compound. If the question refers to formula mass, it is simply noting that the compound is ionic. 

Hydrogen names may also be used for molecular compounds and ions with no tautomerism problems if one wishes to emphasize the conception of the structure as hydrons attached to the anion in question ... 

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