Bonded atoms definition

On the assumption that the pairs of electrons in the valency shell of a bonded atom in a molecule are arranged in a definite way which depends on the number of electron pairs (coordination number), the geometrical arrangement or shape of molecules may be predicted. A multiple bond is regarded as equivalent to a single bond as far as molecular shape is concerned. 

Nucleosides are compounds formed when a base is linked to a sugar via a gly-cosidic bond (Figure 11.10). Glycosidic bonds by definition involve the carbonyl carbon atom of the sugar, which in cyclic structures is joined to the ring... 

For a given molecule and a given intemuclear separation a would have a definite value, such as to make the energy level for P+ lie as low as possible. If a happens to be nearly 1 for the equilibrium state of the molecule, it would be convenient to say that the bond is an electron-pair bond if a is nearly zero, it could be called an ionic bond. This definition is somewhat unsatisfactory in that it does not depend on easily observable quantities. For example, a compound which is ionic by the above definition might dissociate adiabatically into neutral atoms, the value of a changing from nearly zero to unity as the nuclei separate, and it would do this in case the electron affinity of X were less than the ionization potential of M. HF is an example of such a compound. There is evidence, given bdow, that the normal molecule approximates an ionic compound yet it would dissociate adiabatically into neutral F and H.13... 

Like many other chemical concepts the concept of strain is only semi-quantitative and lacks precise definition. Molecules are considered strained if they contain internal coordinates (interatomic distances (bond lengths, distances between non-bonded atoms), bond angles, torsion angles) which deviate from values regarded as normal and strain-free . For instance, the normal bond angle at the tetra-coordinated carbon atom is close to the tetrahedral value of 109.47°. In the course of force field calculations these normal values are defined more satisfactorily, though in a somewhat different way, as force field parameters. 

While this definition of electron-pair covalency neglects the effective charges on the bonded atoms, the designation "homopolar bond appears to be reserved for the special case of an electron-pair bond... 

According to Lewis s (1916) definition, a covalent bond exists whenever two atoms are linked in a stable molecule by sharing two outer electrons. We distinguish between homopolar and heteropolar covalent bonds on the basis of whether or not the bonded atoms are of the same type. Pauling (1960) has shown that in covalent compounds the distance between two elements A and B, independent of the nature of the two atoms, is the same in all compounds containing... 

A definite and distinct, electrically neutral group of bonded atoms. Examples H2 NH3 CH3COOH. mole fraction x The number of moles of molecules (or ions) of a substance in a mixture expressed as a fraction of the total number of moles of ions and molecules in the mixture. 

In other words, whatever the functional form of U+ and 17, the slope of the repulsive term at req must be equal and opposite to the slope of the attractive term. Since the units of dUldr are force, this means that at r = req the forces due to the attractive and repulsive potentials are equal and opposite, that is, there is no net force acting on the bonded atoms, a trivial observation implicit in the definition of equilibrium intemuclear distance. ... 

These properties are common to all definitions of bond energy terms. The advantage of the present scheme is that the qa in any molecule are defined rigorously by the properties of that molecule only. The definition does not imply constancy of bond energy terms from molecule to molecule. These q can be visualized as the work done to stretch two bonded atoms from their original position in a molecule to an infinite distance, while at the same time... 

However, such electron transfer can hardly be called a chemical reaction in the full sense of this term rather it is closer to the class of tunneling phenomena in the physics of solids and electronics. A chemical reaction, by definition, must include the reconstruction of molecules, the spatial rearrangement of atoms, and changes of lengths and angles of valence bonds the definition simply does not apply to small shifts over distances of the order of the zero-point vibration amplitude. 

The interaction between bonded atoms is characterized by the values of p(r), V-p(r), G r) and V(r) at the bond critical point. G(r) is the positive definite kinetic energy density and V(r) is the potential energy density. At a bond critical point, the kinetic and potential energy densities are related to the Laplacian by the local form of the virial relation ... 

QTAIM provides a definitive answer to the question of whether two atoms are bonded or not even in ambiguous cases [87, 88] and, as a consequence, the molecular graph, i.e., the chemical structure, is readily defined by this theory. Two atoms are bonded if their nuclei are linked in space by a line of maximal electron density termed the bond path [89, 90] (see Fig. 1). A single bond path links the nuclei of chemically bonded atoms irrespective of the mode of the bonding covalent (single or multiple), hydrogen, van der Waals, ionic, metallic, etc. The properties of the eleetron density determined at the point of lowest density along the bond path, where... 

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