Mendeleev's periodic table

In a nutshell

Dmitri Mendeleev made one of the first periodic tables in the 19th century. He did this by arranging elements from lightest to heaviest and according to their properties. The modern periodic table is based on his ideas. 

Mendeleev periodic table

Mendeleev wrote down the names of the elements to help him identify patterns. The elements were ordered from lightest to heaviest and arranged in groups based on physical and chemical properties. Interestingly, Mendeleev left gaps in the periodic table for elements that had not been discovered yet. 

Example 

Germanium was undiscovered in Mendeleev's time but once identified it had a place in the periodic table, as Mendeleev left a gap for it.

Modern periodic table

The modern periodic table is largely based on the following ideas of Mendeleev's:

• Elements are arranged in order of increasing atomic numbers
  
• Columns are called groups
• Elements in the same group have similar properties 
• Rows are called periods ​