Beryllium molecule electron configuration

The electronic configuration of the diberyllium molecule, Be2, would be (2cg+)2(2ou+)2, with two bonding electrons being counterbalanced by two anti-bonding electrons, leading to a bond order of zero. The molecule does not exist with such a configuration. Elementary beryllium exists in the solid state with a metallic lattice. 

Lithium and beryllium. Two lithium atoms contain six electrons. Pour will fill the als and tr s orbitals with no bonding. The last two electrons will enter the os, orbital, giving a net bond order of one in the Lk molecule. The electron configuration will be... 

Beryllium hydride, BeH2, has four valence electrons, two from beryllium and one each from the two hydrogen atoms, all of which appear in its Lewis diagram. In VSEPR theory, the steric number is 2, so the molecule is predicted to be linear, and this prediction is verified by experiment. The electron configuration of the central atom is Be (ls) (2s). There are no unpaired electrons to overlap with H(ls) orbitals, so the VB model fails to predict the formation of BeHi. 

El.30 Frontier orbitals of Be Recall from Section 1.9(c) Electron affinity, that the frontier orbitals are the highest occupied and the lowest unoccupied orbitals of a chemical species (atom, molecule, or ion). Since the ground-state electron configuration of a beryllium atom is ls 2s , the frontier orbitals are the 2s orbital (highest occupied) and three 2p orbitals (lowest unoccupied). Note that there can be more than two frontier orbitals if either the highest occupied and/or lowest unoccupied energy levels are degenerate. In the case of beryllium we have four frontier orbitals (one 2s and three 2p). 

In some compounds the number of electrons surrounding the central atom in a stable molecule is fewer than eight. Consider, for example, beryllium, which is a Group 2A (and a second-period) element. The electron configuration of beryllium is ls 2s it has two valence electrons in the 2s orbital. In the gas phase, beryllium hydride (BeH2) exists as discrete molecules. The Lewis structure of BeH2 is... 

Consider the triatomic molecule beryllium chloride (BeCl2). Experimental evidence shows that the BeCl2 molecule in the gas phase is linear with two equivalent Be—Cl bonds, consistent with the VSEPR model prediction. The construction of a valence bond picture of bonding in linear BeCl2 requires the existence of unpaired electrons in Be atomic orbitals that overlap with the half-filled 3p orbital on each Cl to form two equivalent bonds that are 180° apart. However, the ground state electron configuration for Be is ls 2s, which contains no unpaired electrons. 

Beryllium in the beryllium fluoride molecule, BeF2(g), provides an example of sp hybridization (Figure 14 26). The beryllium atom has the electron configuration ls 2s. After hybridization the electrons in the outer shell of the heryllium atom are in two sp hybrid orbitals. Single bonds between the beryllium and fluorine atoms involve the sharing of the unpaired electrons in the sp hybrid orbital of beryllium and the sp hybrid orbitals of the fluorine atom (Figure 14.27). 

Electron diffraction patterns for Beig vapor (, 4) have been interpreted in terms of a linear configuration, with the latter study reporting the Be-1 bond distance as 2.12 A. Other studies also suggest a linear molecule. For example, the electric deflection of mass spectrometrlcaly detected molecular beams (5) showed that all the beryllium dihalides are linear. Snelson (6) observed the infrared spectra of Bel in the spectral range 4000-200 cm using a matrix isolation technique. 

The main dijfference between a linear H3 system and beryllium hydride, BeH2, which is a linear molecule, is that the central atom now contributes two valence electrons and four atomic orbitals the 2s orbital, which is doubly occupied in an isolated ground state Be atom (configuration Is, 2s ), and the three 2p orbitals which are empty in Be but lie not too far above 2s in energy. Graphically, we have ... 

In BeCl2, the chlorine atoms achieve the argon configuration, [Ar], and the beryllium atom has a share of only four electrons. Compounds such as BeCl2, in which the central atom shares fewer than 8 e, are sometimes referred to as electron deficient compounds. This deficiency refers only to satisfying the octet rule for the central atom. The term does not imply that there are fewer electrons than there are protons in the nuclei, as in the case of a cation, because the molecule is neutral. 

To factor out basis set effects, we first compare in Table 24 full configuration interaction (FCI) excitation energies and dipole strengths (the values in parentheses) to those obtained with the TDA, RPA, ACISD, and EOM-CCSD approximations. Because FCI is a very expensive method, which has a factorial dependence on the number of electrons, we are restricted to a small system and present comparisons only for the beryllium atom and the CH" molecule." ... 

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