Lithium molecule, electron configuration

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... 

In this section we consider homonuclear diatomic molecules (those composed of two identical atoms) formed by elements in Period 2 of the periodic table. The lithium atom has a 1 s22s electron configuration, and from our discussion in the previous section, it would seem logical to use the Li Is and 2s orbitals to form the MOs of the Li2 molecule. However, the Is orbitals on the lithium atoms are much smaller than the 2s orbitals and therefore do not overlap in space to any appreciable extent (see Fig. 14.33). Thus the two electrons... 

Lithium —The neutral atom is monovalent and on the loss of one electron the zerovalent singly charged positive ion Li+ is formed. The formation of a negative ion Li" is theoretically possible, this would have the electronic configuration 1 252 and would thus be zerovalent. Such an ion could only be of importance in compounds with more electropositive substances e,g. LiCs, but in molecules such as lithium hydride the contribution to the resonance of the molecule of the form Li" may be considered as negligible. 

Lithium has the electron configuration ls 2sh When lithium metal is heated above its boiling point (1342 °C), Li2 molecules are found in the vapor phase. The Lewis structure for Li2 indicates a Li—Li single bond. We will now use MOs to describe the bonding in Li2. 

L12. (atomic niunber of Li = 3) Six electrons (2 X 3) must be added to the MO s. The four Is inner-shell electrons (2 horn each atom) fill the cTi, and cti, molecular orbitals and so contribute nothing to the bond energy. The two 2s electrons enter the erg, bonding molecular orbital, and therefore Li should be stable. The molecule has been detected in the vapor state of lithium. This MO configuration of Li may be represented as... 

The first four terms in Equation 3.13 represent the attractions between the electrons and the nuclei, and all are negative. The last two terms represent the repulsions between the pair of electrons and the pair of protons, and both are positive. The value of V can be calculated for any configuration of the molecule. But just as in the case of the lithium atom in Section 3.3, this potential energy function does not give a simple pictorial explanation of the stability of the molecule, because there is no exact solution for the motions of four interacting particles. 

Ab initio quantum-mechanical calculations have been made for the two lowest electronic states of the Li02 molecule. For isosceles triangular configurations, the 2A2 state is the ground state, with equilibrium geometry r(LiO) = 1.82 A and 0(0—Li—O) = 44.5°. The 2B2 state is predicted to lie 14 kcal mol-1 higher, with r(LiO)=1.76A and 0(0—Li—0) = 46.5°. For symmetry the 2II state bond distances were predicted, r(Li—Oj = 1.62 A and r(0—0)=1.35A. There appears to be little or no barrier between the C2v and CU forms.150 The decomposition of anhydrous lithium... 

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