Electron shells of atoms
Now let’s return to multielectron atoms. Nucleus of helium is tetrahedron composed of two protons and two neutrons. Tetrahedron is the simplest figure among all space figures. It is the most rigid too, because is composed of triangles. It is obvious that two electrons will occupy two hemispheres around the nucleus. Almost every influence on this shell will result only in its rotation, but won’t violate it (such shell is the simplest among completed ones).
Let’s describe principle of electron shell structure. Divide spherical area around the nucleus into eight equal parts as shown on the picture.
Every new electron will occupy one of the vacant cells. And they will locate symmetrically relative to the nucleus (forces will countervail each other), for example in cells number 1 and 7. in case of existence of four electrons in perinuclear area there may be several variants. For example location of electrons in cells number 1, 3, 6, 8 results in diamond, but in case of their location in cells number 1. 2. 7. 8 we have graphite. In hydrocarbon compounds location of electrons can differ from that ones mentioned above. For example electrons can locate in cells number 1, 2, 3, 4 or 1, 2, 3, 6. So we see origin of possibility of existence of allotropic forms and space and specular isomerism. By the instrumentality of this method we can explain ability of chemical elements to form tetrahedral complexes in coordination chemistry. If we divide perinuclear area into parts by the instrumentality of nodal planes (it is from quantum mechanics), picture will be the same as above.
There are no any wall-bounds between cells. For example three electrons will locate in vertexes of equilateral triangle. And five electrons will form this configuration.
So we can explain organization of atom electron shells in second and third periods of periodic table. And chemical bonds inherent in this atoms directly results from this location of electrons in atoms (look below).
But why there is no possibility to fill electron shells similarly? Because increased charge gives possibility to locate near the nucleus more electrons. In that case common number of electrons will exceed the next magic number 20. It is effect of philosophic law of transforming of quantitative changes into qualitative change (in truth it is effect of principle of continuity).
So metals of long periods have outer electron shell consisting of 20 cells. And shell with 8 electrons will form only by the finishing of the period (we can’t argue with principle of continuity). Explanation of thermal and electric conductivity of metals and semiconductors become easy and clear in this case. Explanations of their magnetic qualities becomes easily too. Theory of chemical bonds in coordination chemistry won’t differ with the same theory for simple compounds.
So let’s draw two atoms of metal schematically.
Vacancies are marked with black arrows. Places of possible joinings of metals in case of alloy are marked with blue arrows. Electrons occupy vacant positions in another atom. Fact that chemical bond can form only by the instrumentality of this method requires for explanation.
There are two types of chemical bonds, but vacancies in electron shells are necessary for both types. Vacancy carries positive charge, electron carries negative one. Chemical bond is based on electric attraction. The first type of bond occurs when electron of one atom fills the vacancy the first type of bond occurs (example is on the picture).
It is the first type – so called ionic bond.
It is the second type - covalent bond.
Vacant areas of two atoms of oxygen are mutually absorbing. Vacant area of one atom is occupied by electrons of another one.
I want you to understand fundamental difference between these types of bonds.
In first case certain area of partially positive charge remains on the surface of molecule (inner electron shells and nucleus of one of the molecule atoms are not fully submerged into common electron surface layer). In case of hydrogen it results in consolidation of separate molecules as a whole.
In second case molecule is covered with electron layer, because in this type of bond every atom grants vacancy and electron. These substances often are gases or are rather inert (examples will be below). Notice that now there is no necessity in Van der Waals forces (which are based on momentary fluctuations of atom electron density).
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