Introduction The new periodicity The comparison of the models Outlook Sources
Home The comparison of the models The periodic table from Mendelejew and Meyer

The comparison of the models

The quantum mechanical states The periodic table from Mendelejew and Meyer The Periodic Table by Bettermann Discussion of both models The quantum-mechanical shell model The gradient term Limits of Quantum Mechanics

The first and secound period The third period The fourth period The fifth period The sixth period The seventh period Summary

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The periodic table from Mendelejew and Meyer

When developing the classic periodic table, Mendeleev and Meyer based on several principles.

- The elements are arranged in sequence according to their atomic number.
- Each period of the system is completed with a noble gas.
- Each period of the system starts with a mono valet element.
- Elements with similar properties are placed under each other.

The growth of valence electrons according to the atomic number is, strictly speaking, only the elements of the s and p shells. Starting from the idea that the elements are lined up according to their atomic number, like pearls on a chain, the elements were successively placed on the possible quantum mechanical states.

In the description of the periodic table, a distinction is made between the shell and the quantum period of the Periodic Table.
With a period of the periodic table is meant a line (up to the seventh) of the lower figure. It is occupied by the individual elements. A period always starts with a monovalent element and ends with an inert gas, which has a closed outer shell. The elements of one period is not necessarily the same principal quantum number assigned.
With a shell is meant a sequence of quantum states, which is formed by a principal quantum number n.

In the figure below shows the currently known Mendelejew- periodic table:

The d and f sub shells were placed between the main group shell s and p. This interruption of the s and p states was considered when allocating the elements on the quantum mechanical states.