Describe how Mendeleev organized the periodic table in terms of atomic mass and the properties of elements and

Question

Describe how Mendeleev organized the periodic table in terms of atomic mass and the properties of elements and explain how the term “periodic” applies to the elements on the periodic table.

Answer 1

Remember that in Mendeleev's time, atomic structure was unknown. He grouped elements with similar physical and chemical properties (reactions with oxygen, water, etc..) together in columns. It became apparent that there was a sequence within each column of the type properties- the most pronounced being the halogens. Each can form a negative -1 ion, but fluorine and chlorine were gases, bromine a liquid and iodine a solid. So these could be ordered within a column. At the end of the columns was a column of the "noble" or inert gases. They could be ordered from lightest to heaviest.

Mendeleev noted that at each level in the column there was a repetition of elements, and this became the basis for the periods.

Mendeleev lumped what were to be known as the transition elements in a separate area, since it was clear they did not react like the metallic elements in the columns.