Final answer:
Members of the Group 18 family of elements were once thought to be inert, but this assumption was proven false.
Step-by-step explanation:
The Group 18 elements, also known as the noble gases, were once thought to be inert or nonreactive due to their filled valence shells.
This means that they have a full shell of two s electrons and six p electrons, making it difficult to remove or add electrons.
However, in 1962, Dr. Neil Bartlett proved this assumption to be false, showing that noble gases can react under certain conditions.