The Modern Periodic Table

While Mendeleev's table in 1869 provided the final coronating step of creating the periodic table, the table itself has gone through a number of changes and additions in recent history.

The table has gone through a wide number of changes ranging from addition of the lanthanides and actinides to the discovery of isotopes.

The first major change actually validated Mendeleev's design and his predictions. Discoveries of elements such as Gallium and Germanium matched his predictions almost perfectly and further reinforced confidence in the layout of his table.

This validated the choices he made when grouping and designating elements. The second change that followed soon after in the 1890's was the discovery of the noble gases.

Given that the discovered gases didn't match any of Mendeleev's groupings, it lead to the creation of a new group, the Noble Gases.

Following the addition of new elements, the biggest change to the table of 1869 was then done in 1913 by Henry Moseley's discovery of the atomic number.

Whilst for over 40 years, the table was ordered by atomic mass, the table would now be ordered by atomic number instead which was a huge shift in the table's orderings.

The change was done as ordering the elements by the number of protons they had better grouped and matched their properties than the number of all particles in its nucleus.

This solved mass-ordering inconsistencies and fixed anomalies. The last big change that morphed Mendeleev's table into the periodic table we see today is the addition of Transuranic and Synthetic Elements.

Due to developments in nuclear capabilities, scientist were able to create new synthetic elements that would otherwise not exist. This new group of elements would expand the table further with the addition of the Super Heavy Metals group.