Beryllium ground state electronic configuration, 19

What is the ground-state electron configuration expected for each of the following elements (a) silver (b) beryllium ... 

Let s look at the ground state electron configuration and orbital diagram of the beryllium atom (4Be) which is the first element in group 2A. 

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). 

Continuing our discussion of atoms of the first ten elements, we go next to beryllium (Z = 4). The ground-state electron configuration of beryllium is or... 

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. 

Solution (a) The central atom is beryllium (Be). The Be atom has two valence electrons with a ground-state electron configuration of [He]2s. The Lewis structure of BeH2 is... 

While from the energy point of view, the correlation effects seem to be overestimated, the RDAf s are particularly satisfactory. Thus, when comparing the 2-RDAf s obtained with these approximations for the ground state of the Beryllium atom with the corresponding FCI one, the standard deviations are 0.00208236 and 0.00208338 for the MPS and IP respectivelyFor this state, which has a dominant four electron configuration of the type, 1122 >, the more important errors, which nevertheless can be considered small, are given in table 2. 

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 ... 

We can now predict the electron configurations and orbital diagrams for the ground state of lithium, which has three electrons, and beryllium, which has four electrons ... 

In beryllium (is2, 2s2) there are in the ground state no unpaired electrons. Uncoupling of the 2s2 electrons, however, gives the configuration is2, zs1zpx, and if this is followed by hybridization two equivalent sp orbitals are produced, the bonds from which are oppositely directed... 

Another manifestation of the reciprocity of densities in r- and p-space is provided by Fig. 19.2. It shows the radial electron number density D r) = Aiir pir) and radial momentum density /(p) = Aitp nip) for the ground state of the beryllium atom calculated within the Hartree-Fock model in which the Be ground state has a ls 2s configuration. Both densities show a peak arising from the Is core electrons and another from the 2s valence electrons. However, the origin of the peaks is reversed. The sharp,... 

Boys S F 1950 Electronic wave functions II. A calculation for the ground state of the beryllium atom Proc. R. Soc. A 201 125-37 Shavitt I 1977 The method of configuration interaction Modern Theoretical Chemistry vo 3, ed H F III Schaefer (New York Plenum) pp 189-275... 

Figure 2.5. The schematic spectrum of the states of the free gaseous beryllium atom showing on the left the orbital scheme with electron occupation and on the right half the term levels. One electron configuration can correspond to several terms. The allowed optical transition is indicated with a bold arrow and the forbidden transitions that correspond with weak absorption in the optical spectrum are indicated with thin arrows between the ground state and the excited states.

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