A single-electron chemical bond is the simplest chemical bond that determines the existence of molecular compounds through the Coulomb confinement of two atomic nuclei by one electron . The main distinguishing features of a single-electron chemical bond is a decrease in the total energy of the molecular system compared to the energy of the isolated atoms and atomic fragments from which it is formed, as well as a significant redistribution of the electron density in the region of the one-electron chemical bond as compared to the simple superposition of the electron density of the atom and atomic fragment close at a communication distance.
The behavior of an electron in a one-electron chemical bond is determined by the laws of quantum mechanics and is described by the Schrödinger equation taking into account the statistical interpretation of the M. Born wave function . In a one-electron chemical bond, the repulsive forces ( Ftt ) of two positively charged atomic nuclei (n + ) are compensated by the attractive force to the only negatively charged elementary particle - the electron (e - ).
A single-electron chemical bond falls outside the scope of both the Lewis electronic chemical bond theory and valence bond theory , since a single-electron chemical bond has neither an electron pair (electron doublet), nor overlap of atomic orbitals , nor electron spin interactions.
The mechanism of the formation of a single-electron chemical bond is described in the framework of the theory of molecular orbitals :
- “The nature of the chemical bond in H 2 + can be explained not only on the basis of the virial theorem, but also on the basis of the Gelman – Feynman theorem . From the charge distribution it follows that the attraction force from spherical symmetric charges centered on the nuclei acts on each nucleus and the overlapping charge centered in the middle between the nuclei. The “own” spherical charge, of course, has no effect on the nucleus. Another spherical charge will only partially shield its core, so that a repulsive force arises between the nuclei anija which, when R = R e is balanced by the attractive force of each core to overlap the electronic charge. " [one]
Thus, in the framework of the theory of molecular orbitals, the charge density in an H 2 + molecule consists of the densities of spherically symmetric charges surrounding each nucleus and an ellipsoidal overlapping charge density; the latter is due to the product of atomic orbitals k and is large only where they have sufficiently large values and strongly overlap. [one]
Content
Single-electron chemical bond length
The length of the one-electron chemical bond in the molecular hydrogen ion H 2 + , numerically equal to the internuclear distance, is 1.06 Å [2] and is equal to twice the Bohr radius a 0 = 0.53 Å — the most probable radius of the electron shell of a hydrogen atom in a stable state. Thus, a one-electron chemical bond in the molecular hydrogen ion H 2 + is formed as if by touching two electron shells of the hydrogen atom (Fig. 2). If in a two-electron chemical covalent bond, half its length determined the covalent radius of an atom, then in a one-electron chemical bond, half its length determines the orbital radius of the atom.
Molecular Alkali Metal Ions
It is known that alkali metals form molecular ions with a single-electron chemical bond. [3]
The characteristic of a single-electron chemical bond in molecular ions of alkali metals is presented in the table.
| Atom | Molecular Ion, Me 2 + | The bond length, d, Å [3] | Orbital radius of an atom, r a , Å |
|---|---|---|---|
| Li | Li 2+ | 3.14 | 1,57 |
| Na | Na 2 + | 3.43 | 1.72 |
| K | K 2 + | 4.18 | 2.09 |
| Rb | Rb 2+ | 4.44 | 2.22 |
| Cs | Cs 2+ | 4.70 | 2,35 |
The existence of molecular ions of alkali metals Li 2 + , Na 2 + , K 2 + , Rb 2 + , Cs 2 + , in which a single valence electron creates a chemical bond, expands and complements the concept of chemical bonds. In these ions, there can be no talk of any interaction of electron spins and overlapping of electron clouds. The only binding electron is localized in the space between the nuclei at the place of contact of the electron shells of atoms and holds them together, forming a chemical system.
See also
- Molecular ion of hydrogen
Notes
- ↑ 1 2 Shustorovich E. M. Chemical bond. The essence and problems. - M .: "Science", 1973. - S. 64-66. - 230 p. - 11,700 copies.
- ↑ Handbook of a chemist. - 2nd ed., Revised. and add. - M. - L .: GNTI chemical literature, 1962. - T. 1. - S. 338. - 1072 p.
- ↑ 1 2 Lidin R.A., Andreeva L.L., Molochko V.A. Handbook of inorganic chemistry. Inorganic matter constants. - M .: "Chemistry", 1987. - 124 p.