Electron cloud representation

Fig. 4.9 Electron cloud representations of the electron density for bonding and anti-bonding tt molecular orbitals.

Figure 7.18 The Is, 2s, and 3s orbitals. Information for each of the s orbitals is shown as a plot of probability density vs. distance (top, with the reiief map (inset) showing the piot in three dimensions) as an electron cloud representation (middle), in which shading coincides...

Figure 7.19 The 2p orbitals. A, A radial probability distribution plot of the 2p orbital shows a single peak. It lies at nearly the same distance from the nucleus as the larger peak in the 2s plot (shown in Figure 7.18B). B, A cross section shows an electron cloud representation of the 90% probability contour of the 2p orbital. An electron occupies both regions of a 2p orbital equally and spends 90% of its time within this volume. Note the nodal plane at the nucleus. C, An accurate representation of the 2pj probability contour. The 2p and 2py orbitals lie along the x and y axes, respectively. D, The stylized depiction of the 2p probability contour used throughout the text. E, In an atom, the three 2p orbitals occupy mutually perpendicular regions of space, contributing to the atom s overall spherical shape.

If we are describing the motion of an electron of known energy or momentum, we can speak only in terms of the probability of finding that electron at a particular position. This leads to the electron-density or electron-cloud representation of electron orbitals. 

Both space-filling and electron density models yield similar molecular volumes, and both show the obvious differences in overall size. Because the electron density surfaces provide no discernible boundaries between atoms (and employ no colors to highlight these boundaries), the surfaces may appear to be less informative than space-filling models in helping to decide to what extent a particular atom is exposed . This weakness raises an important point, however. Electrons are associated with a molecule as a whole and not with individual atoms. The space-filling representation of a molecule in terms of discernible atoms does not reflect reality, but rather is an artifact of the model. The electron density surface is more accurate in that it shows a single electron cloud for the entire molecule. 

Wh] White, H.E., Pictorial Representations of the Electron Cloud for Hydrogen-like Atoms, Physical Review 37 (1931). 

The overlap of the p orbitals in both directions, and the resulting participation of each electron in two bonds, is equivalent to our earlier description of the allyl radical as a resonance hybrid of two structures. These two methods of representation, the drawing of several resonance structures and the drawing of an electron cloud, are merely our crude attempts to convey by means of pictures the idea that a given pair of electrons may serve to bind together more than two nuclei. It is this... 

X-rays are scattered by the electron cloud, so polarized bonds distort the cloud and a true representation of the atomic position is not given. The electron density is distorted towards the electronegative element, and the measured distance is always too short. For example, O-H typically is measured at 0.8 A, which is less than the sum of the ionic radii Neutron... 

A space-filling model shows the electron clouds of each atom as spheres. The clouds overlap when two atoms form a bond. This model is a good representation of the water molecule. ... 

Figure 1.4d shows a schematic representation of the electron "cloud in the ground state of the hydrogen atom. The intensity of the shading gives some idea of the electron density. For this case of a single-electron atom, the electron-density distribution is the same as the probability distribution. However, if more electrons are present, the probability distributions for the individual orbitals must be added together to get the net electron-density distribution in the atom. 

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