In the 19th century, Dmitri Mendeleev organized the elements into an early version of the periodic table.
Cobalt (Co\text{Co}Co) has an atomic weight of 58.9, and nickel (Ni\text{Ni}Ni) has an atomic weight of 58.7. Explain why Mendeleev placed cobalt before nickel in his periodic table.
Mendeleev left several gaps in his periodic table. Explain why his periodic table became widely accepted by the scientific community.
In the modern periodic table, elements are arranged in a different order compared to Mendeleev's table. In order of what property are elements arranged in the modern periodic table?