Mendeleev and the development of the Periodic table

Over time as elements have been discovered scientists have tried to observe patterns in their properties and behaviours, looking to list and categorise them accordingly. 

Döbereiner spotted patterns in sets of 3 elements, he called them triads. Newland arranged elements in order of atomic mass, he found that every 8th element had similar properties (although this did not work exclusively for all elements).  It was Dmitri Mendeleev who really got to grips with categorising elements into a table.  His ideas eventually led to the modern Periodic Table that we have now.   The video below explains the development of the Periodic Table:

So Mendeleev arranged his table in the following way:

• elements were arranged in rows of increasing atomic mass and columns of elements with similar properties,
• gaps were left for yet undiscovered elements, Mendeleev even predicted the atomic masses and properties of these elements. (Once discovered, it was found that he was very accurate with his predictions),
• where elements were in the wrong place when sorted by atomic mass, he swapped then so that they would be grouped by their properties e.g. tellurium and iodine were swapped so that iodine would be grouped with fluorine, chlorine and bromine,
• some elements were paired in the same space.

Mendeleev's table did not include a transition metal block or the Noble gases. As more was discovered about the atom and new elements found the Mendeleev's table evolved into the modern table that we now know.  In recognition of his role the 101st element was named after him - Mendelevium!