Electronic configuration Energy levels

Electronic configuration Energy levels in the shell of an atom which are occupied with electrons symboli2ed by quantum numbers... 

Electron configurations of the r/-transition metal atoms include the s electrons in the outermost occupied shell and the d electrons one energy level lower (e.g., 3r/4r for the first transition series in Period 4). The outer s electrons lie outside the d electrons and are always the first ones lost when transition metals form simple ions. In the first transition series, scandium and zinc each form only one type of cation. Scandium loses its two 4r electrons and its only 3d electron to form Sc ". Zinc loses its two 4r electrons to form Zn. ... 

Chlorine, a member of the halogen family — the VIIA family on the periodic table — often forms cmions. It hcis seven Vedence electrons and a total of 17 electrons, and its electron configuration is ls 2s 2p 3s 3p. So to obtain its full octet, chlorine must lose the seven electrons in energy level 3 or gain one at that level. 

In fact one can go even further back historically to examine whether, or the extent to which, the notion of electronic configurations originated with quantum theory. As the popular account has it, electronic configurations entered physics and chemistry when Bohr first introduced quantum theory into the study of atomic physics. This is perhaps a natural assumption given that there is a sense in which quantization of electron energy is synonymous with the notion of electrons in energy levels or shells. But, surprisingly perhaps, the idea of electrons in shells pre-dates Bohr s model of the atom and has no connection with quantum ideas of any form whatsoever. 

The progression of sections leads the reader from the principles of quantum mechanics and several model problems which illustrate these principles and relate to chemical phenomena, through atomic and molecular orbitals, N-electron configurations, states, and term symbols, vibrational and rotational energy levels, photon-induced transitions among various levels, and eventually to computational techniques for treating chemical bonding and reactivity. 

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