Beryllium molecule

Bands. See Energy bands Barium, values of properties. See Simple metals Barium fluorite. See Fluorites Barium titanate, 450, 466f Beryllium molecule, 28... 

For the beryllium molecule (Be2) the bonding and antibonding orbitals both contain two electrons. In this case the bond order is (2 - 2)/2 = 0, and since Be2 is not more stable than two separated Be atoms, no molecule forms. However, beryllium metal contains many beryllium atoms bonded to each other and is stable for reasons we will discuss in Chapter 10. 

For the beryllium molecule (Be2), the bonding and antibonding orbitals both contain two electrons. In this case the bond order is (2 2)12 = 0. Thus... 

The small lithium Li" and beryllium Be ions have high charge-radius ratios and consequently exert particularly strong attractions on other ions and on polar molecules. These attractions result in both high lattice and hydration energies and it is these high energies which account for many of the abnormal properties of the ionic compounds of lithium and beryllium. 

Beryllium Carbonates. BeryUium carbonate tetrahydrate [60883-64-9] BeCO 4H2O, has been prepared by passing carbon dioxide through an aqueous suspension of beryUium hydroxide. It is unstable and is obtained only when the solution is under carbon dioxide pressure. BeryUium oxide carbonate [66104-25-4] is precipitated when sodium carbonate is added to a beryUium salt solution. Carbon dioxide is evolved. The precipitate appears to be a mixture of beryUium hydroxide and the normal carbonate, BeCO, and usuaUy contains two to five molecules of Be(OH)2 for each BeCO. ... 

There are a few species in which the central atom violates the octet rule in the sense that it is surrounded by two or three electron pairs rather than four. Examples include the fluorides of beryllium and boron, BeF2 and BF3. Although one could write multiple bonded structures for these molecules in accordance with the octet rule (liable 7.2), experimental evidence suggests the structures... 

The formation of the BeF2 molecule can be explained by assuming that, as two fluorine atoms approach Be, the atomic orbitals of the beryllium atom undergo a significant change. Specifically, the 2s orbital is mixed or hybridized with a 2p orbital to form two new sp hybrid orbitals. (Figure 7.12). 

In the BeF2 molecule, there are two electron-pair bonds. These electron pairs are located in the two sp hybrid orbitals. In each orbital, one electron is a valence electron contributed by beryllium the other electron comes from the fluorine atom. 

Therefore we should expect in the gaseous state to find molecules such as BeH2 and BeF2. These molecules have been detected. On the other hand, beryllium has the trouble boron has, only in a double dose. It has two vacant valence orbitals. As a result, BeH2 and BeF2 molecules, as such, are obtained only at extremely high temperatures (say, above 1000°K). At lower temperatures these vacant valence orbitals cause a condensation to a solid in which these orbitals can participate in bonding. We shall discuss these solids in the next chapter. 

The beryllium-fluorine bond is also highly ionic in character. However, there are two such Be-F bonds and the electrical properties of the entire molecule depend upon how these two bonds are oriented relative to each other. We must find the geometrical sum of these two bond dipoles. 

The arrangement of atoms in the molecule of Be40(CH3C00)6. Small circles represent carbon atoms, large circles oxygen atoms. The beryllium atoms occupy the centers of the four tetrahedra. One of the six acetate groups is not shown. 

The arrangement of the centers of the molecules in the crystal is that corresponding to the diamond structure. Each molecule is surrounded tetrahedrally by four molecules. If we consider a molecule as roughly tetrahedral in shape with similar orientation to the tetrahedron formed by the four beryllium atoms, then the adjacent molecules are so oriented as to present tetrahedral faces to one another. 

Under these conditions, the 3-RDM of the three lower states of the Beryllium atom and the two lower ones of the Water molecule were determined [48] by taking as initial data the 2-RDM obtained in a Full Configuration Interaction. In Table 4 some of these results are given and as can be seen they are very satisfactory. 

Figure 8.9 Examples of four-coordinated molecules of beryllium (a) BeCl2 2Et20 and (b) the polymeric molecule BeCl2.

An unusual geometry for oxygen in discrete molecules, the OX4 tetrahedral geometry is found in the oxotetracarboxylates of beryllium such as oxohexaacetatotetraberyllium Be40... 

CH3COO)6 (Figure 8.26). Although this geometry is independent of the nature of the BeO bonds, they are expected to be predominately ionic in this molecule. The same geometry is also found in many three-dimensional infinite structures such beryllium oxide. 

A polymeric structure is exhibited by "beryllium dimethyl," which is actually [Be(CH3)2] (see the structure of (BeCl2) shown earlier), and LiCH3 exists as a tetramer, (LiCH3)4. The structure of the tet-ramer involves a tetrahedron of Li atoms with a methyl group residing above each face of the tetrahedron. An orbital on the CH3 group forms multicentered bonds to four Li atoms. There are numerous compounds for which the electron-deficient nature of the molecules leads to aggregation. 

In solvents that have donor properties, solubility leads to complex formation to give species such as S A1C13 (where S is a solvent molecule). Beryllium chloride is soluble in solvents such as alcohols, ether, and pyridine, but slightly soluble in benzene. 

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