Part c Look at the two question marks between zinc (Zn) and arsenic (As). At the time, no elements were known with atomic weights between 65.2 and 75. But Mendeleev predicted that two elements must exist with atomic weights in this range. What led Mendeleev to predict that two undiscovered elements existed in that range?

part d
The two elements predicted by Mendeleev were discovered later. Locate the elements gallium (Ga) and germanium (Ge) in the periodic table. Click each element to reveal its properties. Explain how these elements fit Mendeleev’s predictions.