Loosely bound electrons

The amount of energy required to remove the most loosely bound electron from a gaseous atom is called the ionisation energy. We can represent this process by the equation... 

The term ionization energy is also applied to the removal of the most loosely bound electron from an atom that has already lost one or more electrons (that is, an ion). Hence the ionization energy of, say, Mg+ is the energy of the process... 

In doped silicon (an extrinsic semiconductor) the doping element has either three or five valence electrons (one electron less or one electron more than the four valence electrons of silicon). Substituting an arsenic or phosphorus atom (five valence electrons) for a silicon atom in a silicon crystal provides an extra loosely-bound electron that is more easily excited into the CB than in the case of the pure silicon. In such an n-type semiconductor, most of the electrical conductivity is attributed... 

The classical nonrelativistic expansion goes over jp- jm . In the case of the loosely bound electron, the expansion in jp IrrP corresponds to expansion in (Za) hence, relativistic corrections are given by the expansion over even powers of Za. As we have seen above, from the explicit expressions for the energy levels in the Coulomb field the same parameter Za also characterizes the binding energy. For this reason, parameter Za is also often called the binding parameter, and the relativistic corrections carry the second name of binding corrections. 

The periodic system developed from Bohr s atomic theory is of the greatest importance in chemical science because it demonstrates that the properties of the elements depend on their positions in the system. It is immediately apparent that chemical valency depends on the number of loosely-bound electrons in the atom. Thus, the alkali metals have one such electron while the divalent alkaline-earth metals have two, etc. Valency is therefore closely connected with electronic structure and provides the foundation for the modern theory of the chemical bond, the basis of which is to be found in the coupling or transfer of the valency electrons. 

Electrons in a solid or a liquid may be separated into two groups the core electrons which are the inner, tightly bound electrons with properties sometimes known by studying isolated atom or molecule, and the valence electrons which are the outer, relatively loosely bound electrons. The valence electrons are highly sensitive to the state of aggregation of the system. For our present discussion we might consider as valence electrons the outer 3s electron detached from a sodium atom in liquid ammonia, or the excess electron in a liquid rare gas. 

Metallic Solids In such solids the metal atoms are held together by metallic bonds. In metallic bonding a regular lattice of positive kernels are held together by a cloud of loosely bound electrons. These electrons are free to move together the lattice, e.g. Ag, Au, Na, Cu, Fe, K, Al, etc. 

Finally, there is the metallic bond that occurs between metals. The atoms of metals hold onto their electrons very loosely, which is why metals conduct electricity so well. The loosely bound electrons are often referred to as the sea of electrons. The darker circles in Figure 5.19 represent the electron clouds of the metal atom. 

Processes (19.61)-(19.63) are similar to electron-impact processes (19.33), (19.34) and (19.25), except that in the present case the intermediate (H-7) resonant state is formed not by capture of a free electron but rather by capture of loosely bound electron from 11. There may be also other mechanisms for electron detachment processes (19.61) and (19.63) and for the dissociation process (19.62). 

Only the most loosely bound electrons in an atom or molecule need be considered explicitly, the valence electrons being separated from a core , whose presence is simulated by using a suitable effective (valence-only) Hamiltonian - or, in practice, by assigning empirical values to the Coulomb and exchange integrals involving valence orbitals. 

J. Jortner, Mol. Phys., 5, 257 (1962). Dielectric Medium Effects on Loosely Bound Electrons. 

Structural asymmetry and dissymmetry can be made amenable to theoretical treatment by showing in a general way that electromagnetic waves can perturb charged particles, of which molecules are constructed, so as to produce rotatory phenomena. A charged particle, which we may take to be a loosely bound electron for the reason that rotatory power originates almost entirely from electronic rather than nuclear motions, will oscillate... 

---