Periodic Table; Effective Nuclear Charge (Sections)The prefix eka- comes from the Sanskrit...

Periodic Table; Effective Nuclear Charge (Sections)

The prefix eka- comes from the Sanskrit word for “one.” Mendeleev used this prefix to indicate that the unknown element was one place away from the known element that followed the prefix. For example, eka-silicon, which we now call germanium, is one element below silicon. Mendeleev also predicted the existence of eka-manganese, which was not experimentally confirmed until 1937 because this element is radioactive and does not occur in nature. Based on the periodic table shown in Figure, what do we now call the element Mendeleev called eka-manganese.

▲ Figure Discovering the elements.

Copper, silver, and gold have all been known since ancient times, whereas most of the other metals have not. Can you suggest an explanation?