Chemical bonding covalent bonds

Electronic structure calculations for transition metal carbides (Neckel 1990, Le 1990, Le et al. 1991) reveal significant contributions to cohesion by all three main types of chemical bonding. Covalent bonds are due to the formation of molecular orbitals by combining atomic d-orbitals of the metal with p-orbitals of C. Ionic bonds result from charge transfer from the metal to the non-metal. Metallic bonds are due to s electrons and also to a non-vanishing density of d-p electronic states (DOS) existing at the Fermi level (Figure 7.30). The main difference between the DOS curves calculated for stoichiometric ZrC, TiC or HfC and NbC, TaC or VC is... 

In this chapter we have been looking at three types of chemical bonds covalent bond, ionic bonds and metallic bonds. The bonds are described by using different models and theoiy which introduce the molecular orbitals. These molecular orbitals are formed from atomic orbitals which we heard about in chapter 1. 

Formation of a chemical bond—covalent bonding would be strong and van der Waals bonding would be weak. 

A chemical bond is the physical phenomenon responsible for the attractive interactions between atoms that confers stability to di- and polyatomic chemical compounds. There are mainly three kinds of chemical bonds covalent bonds, ionic bonds, and hydrogen bonds. Generally covalent and ionic bonds are often described as strong, whereas hydrogen bonds and van der Waals are generally considered to be weaker. 

The most important orbitals are those in the outer shells, which are involved in the formation of chemical bonds. Covalent bonds are formed when atomic orbitals overlap and merge to form molecular orbitals (Chapter 14). 

Successful numerical solution of the Schrodinger equation has yielded energies and properties of atoms and molecules, but not yet a clear physical explanation of chemical bonding. There is even a controversy on the mechanistic origin of the most simple chemical bond, covalent bonding, as it was remarked by Burdett in his classical book [2]. 

Over the years, different approaches have been developed to reveal chemical bonds. Covalent bonds are intuitively represented using conventional Lewis stractures [19]. Molecular Orbital (MO) theory has been veiy useful and successfiil for the theoretical analysis of chemical reactions and chemical reactivity. The frontier orbital theory [20] and the orbital symmetry rules of Woodward and Hoffman [21] are paradigmatic examples of the possibilities of quantum chemistry within the MO theory. 

In the creation of network structures by chemical bonding (covalent bonding), there is a method of (1) crosslinking at the same time as polymerization or (2) crosslinking by chemical reaction after linear polymer chains have been synthesized. The latter method can be further divided into the addition polymerization in the presence of divinyl conqjounds (radical polymerization, anionic polymerization, ionic polymerization, etc.) or the formation of crosslinked structures by polycondensation of multifunctional compoimds. In the addition reaction, free radical polymerization is generally utilized. In this free radical polymerization method, initiators are usually used, but light, radiation, and plasmas can also be used. 

A chemical bond is a pooling of electrons between two atoms. The trigger of this pooling is the stabilization of atoms by saturation in electrons of their valence layers. The difference of electronegativity between two atoms determines the nature and force of their connection. Among the several kinds of chemical bonds, covalent bonds and ionic bonds are nsnally nsed as references. 

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