Electron charge clouds

Dispersion forces caimot be explained classically but a semiclassical description is possible. Consider the electronic charge cloud of an atom to be the time average of the motion of its electrons around the nucleus. 

Since nuclear masses are much greater than the electron mass we can treat the nucleus as if it were fixed in space. Taking the mass of the electron charge cloud as m, then k = mu>Q where angular frequency of the oscillator. 

This moment measures the extent and direction of the shift of an atom s electronic charge cloud with respect to the nucleus. The quantity M(fi) can effectively be regarded as an intra-atomic dipole moment. The intra-atomic dipole moment of each atom contributes to the... 

In the same way that electronegativities determine the polarity of diatomic interactions, ionization radii should define the effective electronic charge clouds that interpenetrate to form diatomic molecules, as shown schematically in Figure 5.3. The overlap of two such spheres defines a lens of focal lengths fixed by the ionization radii, r and r2, at an interatomic distance d = x i + x2-... 

This electron density p(r) corresponds to the fuzzy "body" of the electronic charge cloud, providing a representation for the shape of the molecule. 

In the general scheme described in subsequent sections, a functional group is regarded as a fuzzy body of electronic charge cloud, a fuzzy subset of the electronic charge density cloud of the complete molecule. In this context, a functional group is a special case of a fuzzy fragment of a molecular body, obtained by some subdivision... 

But now it has been shown [cf. equation (30) above] that the binding energies of atoms are closely related to the electrostatic potential created at the nucleus by the electronic charge cloud. If we assume the unperturbed charge cloud to be that of a neutral atom (Z-1, Z— 1), then its interaction with the nucleus is increased by a factor Z/Z— 1 on adding a proton and this strongly suggests that one should form the quantity (Z,Z—1)-(Z/Z— l)i (Z—1,Z— 1). One obtains from the 1/Z expansion... 

In quantitative modeling of PESs the description of the molecular shape as a superposition of atomic components remains an attractive approach, but it is clear from the earlier discussion that it must be extended to accommodate two important factors. The atomic shape is not a rigid, but rather a soft, exponentially decaying electronic charge cloud. In addition, it should be anisotropic with the anisotropy depending not only on the atom itself, but also on its partner in the chemical bond. 

The constant d is commonly taken to be 34.5 pm. It derives from the repulsive effects of overlapping electron charge clouds. 

The magnitude of inter-electronic repulsion is inversely proportional to the distance r between the regions of maximum charge density of d-orbitals which are occupied by electrons. This repulsion would decrease only if the distance r increases or the lobes of d-orbitals extend in space. The extend on ofthe lobes of the af-orbitals which means the expansion of d-electron charge cloud is known as nephelauxetic effect. Thus in the complex the electron charge cloud is more diffuse than in the free ion, hence, the average electron-electron distance is greater in the complex. 

Most of the carbon atoms in a diamond in a necklace have 6 protons, 6 neutrons, and 6 electrons. The protons and neutrons are in the nucleus, which is surrounded by a cloud of negative charge created by the 6 electrons. You will learn more about the shapes and sizes of different atoms electron clouds in Chapter 11. For now, we will continue to picture the electron-charge clouds of all the atoms as spherical (Figure... 

Space-filling model A way of representing a molecule to show a somewhat realistic image of the electron-charge clouds that surround the molecule s atoms. 

Describe the hydrogen molecule, including a rough sketch of the electron-charge cloud created by its electrons. 

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