Lithium atom orbital energies

For purposes of illustration, consider a lithium crystal weighing one gram, which contains roughly 1023 atoms. Each Li atom has a half-filled 2s atomic orbital (elect conf. Li = ls22s1). When these atomic orbitals combine, they form an equal number, 1023, of molecular orbitals. These orbitals are spread over an energy band covering about 100 kJ/moL It follows that the spacing between adjacent MOs is of the order of... 

The energy of the one-electron bond in the lithium molecule ion is calculated with consideration of the s-p separation to be 1.19 e. v and the hybrid bond orbital involved is shown to involve about equal contributions from the 25 and 2p orbitals of the lithium atom. 

In the molecule Li2 the bond involves a hybrid atomic orbital as+bp formed from the 2s orbital and one of the much less stable 2p orbitals. It is shown below that the amount of p character of this bond orbital (equal to b2, with a2 + b2 = 1) is small, being about 8%. On the other hand, if each of the atoms in metallic lithium requires a bond orbital and a metallic orbital and the two are equivalent they will be 2- -p) and 2 t(s —p), with 50 % p character. The analysis of energy quantities supports this conclusion. 

A lithium atom has three electrons. The first two electrons fill lithium s lowest possible energy level, the 1. S orbital, and the third electron occupies the 2 5 orbital. The three representations for the ground-state electron configuration... 

A) and for the 1 s orbital, the average distance =- q-1 bohr is 2.25 bohr for q = 2/3. From both this point of view, and that of the ionization energy, the latter quarkonium atom is rather comparable to the lithium atom, and expected to be chemically highly reactive. 

In the lithium atom, and for all other multi-electron atoms, orbitals in different energy sublevels differ in energy. 

The band of molecular orbitals formed by the 2s orbitals of the lithium atoms, described above, is half filled by the available electrons. Metallic beryllium, with twice the number of electrons, might be expected to have a full 2s band . If that were so the material would not exist, since the anti-bonding half of the band would be fully occupied. Metallic beryllium exists because the band of MOs produced from the 2p atomic orbitals overlaps (in terms of energy) the 2s band. This makes possible the partial filling of both the 2s and the 2p bands, giving metallic beryllium a greater cohesiveness and a higher electrical conductivity than lithium. 

Let us consider what happens as two s-valent atoms A and are brought together from infinity to form the AB diatomic molecule as illustrated schematically in Fig. 3.1. The more deeply bound energy level EA could represent, for example, the hydrogenic Is orbital (EA = —13.6 eV), whereas the less deeply bound energy level EB could represent lithium s 2s orbital (EB = — 5.5 eV. cf Fig. 2.16). Each free atomic orbital satisfies its own effective one-electron Schrodinger equation (cf eqn (2.59)), namely... 

For hydrogen, only the Is orbital is energetically accessible for band formation. For elements of lithium through fluorine, the 2s and, at somewhat higher energy, the three 2p orbitals are available, and, depending on the ways in which the atomic orbitals align with the crystal structure, these may form either a continuous s,p band or a pair of bands with the same... 

Fig. 7.20 Interaction of eight 2s orbitals of eight lithium atoms. The spacing of the energy levels depends upon the geometry of the cluster...

The chiral discrimination in the 2 1 complexes (homo vs. heterochiral ones) indicates that, in all the cases, the heterochiral complexes are more stable than the homochiral ones, except for the tert-butyl derivatives. The chiral discrimination energies were discussed on the basis of different parameters related to the lithium atom, such as the N-Li distance, the orbital interaction between the lone pair of the nitrogen and an empty orbital of the lithium, and its atomic contribution to the total energy of the complexes. 

Electron configurations describe the exact arrangement of electrons (given as a superscript) in successive energy levels or shells (1,2,3, etc.) and orbitals (s, p, d, f) of an atom, starting with the innermost electrons. For example, a lithium atom s configuration is ls 2sT The superscripts mean two electrons are in the Is orbital and one electron is in the 2s orbital. Several rules are applied to the filling of electrons ... 

In lithium, atomic number 3, the Is level has dropped to a very low energy and is occupied by two electrons. The Is orbital is considered part of the atomic core of lithium a single electron occupies a 2s orbital. In the lithium row, all elements, to neon, Z= 10, have a lithium core the energy levels in successive atoms... 

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