Lone pair electrons water

FIGURE 13.5 Isosurface plots, (a) Region of negative electrostatic potential around the water molecule. (A) Region where the Laplacian of the electron density is negative. Both of these plots have been proposed as descriptors of the lone-pair electrons. This example is typical in that the shapes of these regions are similar, but the Laplacian region tends to be closer to the nucleus. 

Bismuth Trifluoride. Bismuth(III) duoride is a white to grey-white powder, density 8.3 g/mL, that is essentially isomorphous with orthorhombic YF, requiring nine-coordination about the bismuth (11). It has been suggested that BiF is best considered an eight-coordinate stmcture with the deviation from the YF stmcture resulting from stereochemical activity of the bismuth lone-pair electrons. In accord with its stmcture, the compound is the most ionic of the bismuth haUdes. It is almost insoluble in water (5.03 0.05 x 10 M at pH 1.15) and dissolves only to the extent of 0.010 g per 100 g of anhydrous HF at 12.4°C. 

Q The nitrogen lone-pair electrons expel water, giving an iminium ion. 

Elimination of water by the lone-pair electrons on nitrogen then yields an intermediate iminium ion. 

A hydrogen bond is formed between a hydrogen atom and a lone pair electrons from an atom in a neighboring molecule. For example, the hydrogen atom of a water molecule forms a hydrogen bond with the lone pair of electrons from an oxygen atom in another water molecule. 

The ditrigonal cavity formed by six corner sharing silica tetrahedra (Fig. 3.10) has a diameter of 0.26 nm and is bordered by six sets of lone-pair electron orbitals emanating from the surrounding ring of oxygen atoms. These structural features - as is pointed out by Sposito (1984) - qualifies the ditrigonal cavity as a soft Lewis base capable to complex water molecules (and possibly other neutral dipolar molecules). 

A plot of the Lennard-Jones 9-3 form of Equations 7 and 8 for ST2 water interacting with smectite and mica surfaces is shown in Figure 1. Values for the parameters used in Figure 1 are given in Tables II and III, and in reference (23). The water molecule is oriented so that its protons face the surface and its lone pair electrons face away from the surface, and the protons are equidistant from the surface. Note that the depth of the potential well in Figure 1 for interactions with the smectite surface and mica surface are... 

Each water molecule can form four hydrogen bonds since it contains two O—H bonds and two unshared electron pairs (Fig. 2.7). Thus, two bonds are formed by means of the molecule s own H atoms and two by means of two lone-pair electrons (Fig. 2.7). These four hydrogen bonds are directed in the four tetrahedral directions in space (Fig. 2.4). 

The simplest compounds to consider here are ammonia and water. It is apparent from the above electronic configurations that nitrogen will be able to bond to three hydrogen atoms, whereas oxygen can only bond to two. Both compounds share part of the tetrahedral shape we saw with 5/ -hybridized carbon. Those orbitals not involved in bonding already have their full complement of electrons, and these occupy the remaining part of the tetrahedral array (Figure 2.21). These electrons are not inert, but play a major role in chemical reactions we refer to them as lone pair electrons. 

These orbital pictures tend to get a little confusing, in that we really need to put in the elemental symbol to distinguish it from carbon, and we usually wish to show the lone pair electrons. We accordingly use a compromise representation that employs the cleaner line drawings for part of the structure and shows the all-important orbital with its lone pair of electrons. These are duly shown for ammonia and water. 

A coordinate covalent bond forms between the aluminum and the hydrating water molecules. Aluminum is a Group lllA element, so the aluminum (111) cation (with a chcirge of -1-3) formally has no valence electrons. The oxygen of water has lone pairs. Therefore, water molecules most likely hydrate the cation by donating lone pairs to form coordinate covalent bonds. In this respect, you can call the water molecules ligands of the metal ion. 

A) Electrostatic effect the coordination of two water molecules may be represented as in (II). Now it is known from the work of many people (e.g. Ellison and Shull [4], Duncan and Popls [6], Bubnelle and Coulson [6], Hamilton [7]) that the total dipole moment in a single water molecule arises partly from the separate 0—H bonds and partly from the lone-pair electrons in each oxygen atom. Thus the... 

A nucleophile such as water uses its lone pair electrons ( ) to attack and forms a neutral addition compound by proton transfer ... 

Normally full valence MCSCF calculations (choosing all valence orbitals as active) represent a balanced treatment of correlation. However this is not always the case, especially not in systems containing lone-pair electrons. For example, a full valence MCSCF calculation for the water molecule yields less accurate values for the bond distance, the bond angle, and the dipole and quadrupole moment than an SCF calculation. The reason is that there are only two orbitals available for correlating the eight valence electrons (the 4ax and the 2b2 orbitals). Thus correlation is only introduced into the lone-pair orbital... 

Hydrophilic Groups. Water solubility can be achieved through hydrophilic units in the backbone of a polymer, such as O and N atoms that supply lone-pair electrons for hydrogen bonding to water. Solubility in water is also achieved with hydrophilic side groups (e.g., OH, NHi,C02, SOy ). Truly unique in its ability to interact and promote water solubility is the -O-CH2-CH2- group. The interactions of these groups with water and their placement in the polymer structure influence the waler solubility of the polymer and its hydrodynamic volume. 

The carbon-oxygen double bond in aldehydes and ketones is similar and can be described in either of these two ways. If we adopt the iocalised-orbital description, formaldehyde will have two directed lone pairs in place of two of the C-H bonds in ethylene. In this case the axes of these hybrid orbitals will be in the molecular plane (unlike the oxygen lone pairs in water). Either the components of the double bond or the lone pairs can be transformed back into symmetry forms. The alternative description of the lone pairs would he one er-type along the 0-0 direction and one jr-type with axis perpendicular to the 0-0 bond hut in the molecular plane. It is the latter orbital which has the highest energy, so that an electron is removed from it in. ionisation or excitation to the lowest excited state. 

In water, four valence electrons form two lone pair orbitals that have been determined (Pople, 1951) to point above and below the plane formed by the three nuclei (H—O—H) of the molecule. The shared electrons with the protons give the molecule two positive charges, and the lone pair electrons give the molecule two negative charges. The result is a molecule with four charges and a permanent electric dipole (McCelland, 1963) of 1.84 Debye. 

In mixtures water and solvents with lone pair electrons, the structure depends on the base strength of the lone pair electrons in the series given on page 9. For example the spectra of water-dioxan (Fig. 14) show a weaker frequency shift in comparison with water-alcohol mixtures (Fig. 12) — that means weaker H-bonds — of the H-bond band of water (1.92 q instead 1.94 /a). The wavelength 1.896 ju in Fig. 14 of the non H-bonded OH band instead 1.89 ju in water/methanol (Fig. 12) corresponds with a non H-bonded water OH group whose second OH is H-bonded (Compare the free OH band in liquid water 200 °C < T< 350° in Fig. 1249 ). 

The phosphazene backbone itself appears to be hydrophilic, due mainly to the presence of the nitrogen lone-pair electrons and their ability to form hydrogen bonds to water molecules. However, the overall hydrophilic or hydrophobic character is determined by the side groups and by the degree to which they shield the skeleton. 

Where more than one possible shape exists, the shape depends upon the number and position of lone pairs. Lone pairs, n electrons, and ring strain can distort the predicted bond angles. Lone pairs and x electrons require more room than bonding pairs. For example, the lone pairs on water make the bond angle 104.5°. 

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