Why is the number of electrons in the secondary outer shell 8

Modern atomic physics points out that the electron configuration outside the nucleus of an atom follows the principle of lowest energy, Pauli's principle of incompatibility, and Hunt's rule.

The so-called principle of lowest energy means that each atomic orbital has a certain amount of energy, and electrons are always distributed in the orbital with the lowest energy. For an atom, it has eight atomic orbitals with lower energy and ten atomic orbitals with higher energy distributed in its m-layer orbitals, while the eight orbitals with lower energy are less than the n-layer and the higher ten energies are higher than the two atomic orbitals in the n-layer. Therefore, generally speaking, the m layer can have 18 electron arrangements when it is the subouter shell, and only 8 electrons can be arranged when it is the outermost shell.

The electron shell after the m shell has such similar atomic orbitals, so the subouter shell can accommodate more than 8 electrons.

In the first few electron shells before the m layer (excluding the k shell, which has only two atomic orbitals), it only has 8 atomic orbitals with lower energy, so it can only accommodate 8 electrons when it is a subouter shell.

Number of electrons in the subouter shell: The number of electrons in the penultimate shell.

For example, there are 8 electrons outside the oxygen nucleus, the number of electrons in the first shell is 2, and the number of electrons in the second shell is 6, that is, the number of electrons in the secondary outer shell is 2

There are a total of 16 electrons outside the sulfur nucleus, the number of electrons in the first shell is 2, the number of electrons in the second shell is 8, and the number of electrons in the third shell is 6, that is, the number of electrons in the subouter shell is 8

Electron Arrangement Rules:

The maximum number of electrons contained in each electron shell is 2n 2 (n is the number of the electronic shell). The number of electrons in the outermost shell does not exceed 8 (no more than 2 when the k-layer is the outermost). The number of electrons in the subouter shell does not exceed 18, and the number of electrons in the penultimate shell does not exceed 32.

Electrons outside the nucleus are always arranged in the lowest energy electron shell first, and then from the inside out, the L layer is arranged before the M layer. The above four laws are interrelated and cannot be understood in isolation.

The secondary electron shell refers to the penultimate shell of the atom (excluding h, he).

There are only two possibilities for this to happen, and one is the inert gas argument. The outermost layer of noble gas is 8 electrons, and it is not easy for other elements to react to form compound beams, so it is 0 valence.

The second is elemental, which is composed of the same element, and the shift of electrons is uniform and not electrical. So also acorn is 0 price.

If there are 2 electron layers in the trouser spine, it is 2 electrons in the first Hu layer, and the second layer is also 2 electrons, and the sum of the number of electrons in the outermost shell and the number of electrons in the subouter shell is less than 8, if there are 3 electron layers, the subouter shell is the second layer is 8 electrons, and the outermost shell is also 8 wild bending electrons, and the sum of the number of electrons in the outermost shell and the number of electrons in the subouter shell is less than 8, so it is 4 beryllium, so B is selected