Covalent bonds of molecules

The single covalent bond consists of an electron shared between two atoms. There are three main ways of covalent bonding, of molecules such as methane (Fig. 2.2) ... 

Use electronegativities to classify covalent bonds of molecules, and determine whether covalent molecules are polar or nonpolar. (Section 4.9)... 

Alternatively a reaction between a species with a pair of electrons and a species with a vacant orbital to form a covalent bond, heteronuclear molecule See homonuclear molecule. 

In this molecule, the aluminium receives a pair of electrons from the nitrogen atom. The nitrogen atom is referred to as a donor atom and the aluminium as an acceptor atom. Once the bond is formed it is identical to the covalent bond of previous examples it differs... 

Root-mean-square end-to-end distance, which effectively takes account of the average distance between the first and the last segment in the macromolecule, and is always less that the so-called contour length of the polymer. This latter is the actual distance from the beginning to the end of the macromolecule travelling along the covalent bonds of the molecule s backbone. Radius of gyration, which is the root-mean-square distance of the ele-... 

There are also molecules that are exceptions to the octet rule because one of the atoms has fewer, rather than more than, eight electrons in its valence shell in the Lewis structure (Figure 1.19). These molecules are formed by the elements on the left-hand side of the periodic table that have only one, two, or three electrons in their valence shells and cannot therefore attain an octet by using each of their electrons to form a covalent bond. The molecules LiF, BeCl2, BF3, and AIC13 would be examples. However, as we have seen and as we will discuss in detail in Chapters 8 and 9, these molecules are predominately ionic. In terms of a fully ionic model, each atom has a completed shell, and the anions obey the octet rule. Only if they are regarded as covalent can they be considered to be exceptions to the octet rule. Covalent descriptions of the bonding in BF3 and related molecules have therefore... 

In contrast, covalent bonding involves the sharing of electron pairs between two specific atoms, and it is possible to speak of a definite bond. For example, in molecules of H, and CC14 there are one and four covalent bonds per molecule, respectively. 

The building blocks of supramolecular systems are held together by intramolecular interactions and these systems are reversible. This intrinsic property is not only a consequence of the more labile interactions within supermolecules, compared to covalent bonds in molecules, but reversibility is essential for the function expressed by supramolecular systems. Kinetics can never be inferred from thermodynamic studies. For example, the knowledge of a host-guest equilibrium constant does not... 

Hydrogen-bonding has a huge influence on the physical properties of molecules. Boiling is the conversion of a liquid (where the molecules are free to move, but linked by intermolecular bonds) to a gas, where (in an ideal gas) the molecules are so distant from each other that they do not interact. Boiling, therefore, does not break the strong covalent bonds within molecules, but rather the weaker intermolecular bonds between them. 

The energy equation 3-3 may be used to define the ion energy level of ionic compound molecules. Fmthermore, this energy equation may also be used to define the ion energy level in covalently bonded compoimd molecules, though the physical meaning of the ion level in covalent compounds is a matter of discussion. 

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