Spherical electron cloud

All ionic bonds have some covalent character. To see how covalent character can arise, consider a monatomic anion (such as Cl ) next to a cation (such as Na ). As the cation s positive charge pulls on the anion s electrons, the spherical electron cloud of the anion becomes distorted in the direction of the cation. We can think of this distortion as the tendency of an electron pair to move into the region between the two nuclei and to form a covalent bond (Fig. 2.11). Ionic bonds acquire more covalent character as the distortion of the electron cloud on the anion increases. 

FIGURE 3.11 For large separations, the complicated interaction between the 37 charged particles in K+ and the 35 charged particles in Cl- reduces to simple Coulombic attraction between the two net charges. Effects from the spherical electronic clouds and the small nucleus tend to cancel (see Figure 3.2). 

The value of n also determines the number of breaks, or discontinuities in the electron cloud. For example, if the cloud is shaped like a dumbbell with a very thin handle, essentially all of the cloud lies between the two spherical sections at the extremities a tiny ultramicroscopie investigator would note a discontinuity when he walked out of one sphere onto the handle. Another type of discontinuity may exist in a spherical electron cloud while some spherical clouds seem to be just one piece, other electrons consist of a central spherical section with one or more spherical shells surrounding the central section. The same investigator would note a break when crossing the zero-probability region, while... 

It might be said in extenuation of the hydridic model that, according to the ideas of Kimball (19), the H atom should enter a more or less spherical electron cloud representing an unpaired electron associated with a metal atom. Thus, LiH is represented in Kimball s theory as a pair of tangent electron cloud spheres, or spheroids, each comprising two electrons of opposite spin centered about a +3 and a +1 nucleus, respectively. This picture is equally applicable to the hydrogen in CH4, HC1, or a metallic hydride—i.e., in all cases hydrogen is surrounded by a pair of electrons. 

The first and second terms of equations 3.99 and 3.100 represent the spherical electron clouds, corresponding to the presence of the electrons at the nuclei whilst the third term describes the exchange cloud, which is elliptical in shape. This we shall term the transitional structure as for the hydrogen molecule ion. 

Figure 1.8.2. The sodium ion is inducing a temporary dipole In an atom with a normally spherical electron cloud. The induced dipole is causing another atom to have a momentary dipole. These temporary dipole attractions are sufficient to cause even noble gases to condense at low temperatures.

A cation s positive charge attracts the electrons of an anion or atom in the direction of the cation distortion of spherical electron cloud). 

We have seen that when two neutral atoms with their positive nuclei surrounded by spherical electronic clouds approach each other, this results in a strong distortion of the electronic clouds and finally leads to the formation of more stable molecules where the nuclei adopt fixed relative positions and are surrounded by electrons that occupy new orbitals around them. More precisely, the inner orbitals of the atoms of the molecule are but slightly modified with respect to those of the isolated original atoms. The outer orbitals are completely... 

The intensity of shading at any point represents the magnitude of 1, i.e. the probability of finding the electron at that point. This may also be called a spherical charge-cloud . In helium, with two electrons, the picture is the same, but the two electrons must have opposite spins. These two electrons in helium are in a definite energy level and occupy an orbital in this case an atomic orbital. 

Strictly speaking, the size of an atom is a rather nebulous concept The electron cloud surrounding the nucleus does not have a sharp boundary. However, a quantity called the atomic radius can be defined and measured, assuming a spherical atom. Ordinarily, the atomic radius is taken to be one half the distance of closest approach between atoms in an elemental substance (Figure 6.12). 

Figure 2 depicts different forms of chemisorption for a Na atom and a Cl atom on the NaCl lattice (5). Figure 2a corresponds to weak binding of a Na atom to the lattice. We investigated this type of bond in 1947 (6-5). The bond is effected by the valence electron of the Na atom, which is to a greater or lesser degree drawn into the lattice. In other words, the electron cloud surrounding the positive framework of the Na atom, which in case of the isolated atom was spherically symmetrical, is now deformed and... 

It is an interesting Tact that just as the single s orbital is spherically symmetric, the summation or electron density of a set or three p orbitals, five d orbitals, or seven f orbitals is also spherical (UnsBld s theorem). Thus, although it might appear as though an atom such as neon with a filled set of sand p orbitals would have a lumpy electron cloud, the total probability distribution is perfectly spherical... 

Instead of drawing the s-orbital as a cloud, we usually draw its boundary surface, a surface that encloses the densest regions of the cloud. The electron is likely to be found only inside the boundary surface of the orbital. An s-orbital has a spherical boundary surface (Fig. 1.24), because the electron cloud is spherical. s-Orbitals with higher energies have spherical boundary surfaces of greater diameter. They also have a more complicated radial variation (Fig. 1.25). 

---