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.