Question

________having higher atomic weight was placed before Nickel.

Answer 1

Mendeleev periodic table:

• In Mendeleev, periodic table elements were arranged based on increasing atomic mass.
• During Mendeleev, only 63 elements were known so after studying the properties of elements he arranged them into vertical columns called groups, and horizontal rows called periods.
• During the arrangement, there were seven periods and eight groups in Mendeleev's periodic table.

Although Mendeleev resolved many of the previous limitations in previous arrangements but is suffered from some limitations such as:

Anomalous pair: Some elements with higher atomic weight were placed before low atomic weight elements in order to maintain the similar chemical nature of elements and are called inverted pairs or anomalous pairs.

Cobalt (58.9) with a higher atomic mass precedes Nickel (58.6) in the periodic table.

Therefore, Cobalt having a higher atomic weight was placed before Nickel.