Chemistry topic one - the periodic table

T1

The periodic table

History of the periodic table 

1800’s

Before discovering protons, neutrons and electrons, scientists tried to classify the elements by arranging them in order of their atomic weights. The atomic weight of an element is equivalent to what we now call its relative atomic mass.

Early periodic tables were incomplete, since many elements were unknown. Also, some elements were placed in groups with elements that were not similar to them because they didn't take into account their properties 

Dmitri Mandeleev - 1869

In it, he arranged the elements in order of increasing atomic weights

He took into account the properties of the elements and their compounds

He left gaps in his table…