a) Why do we classify elements?
b) What were the two criteria used by Mendeleev in creating his Periodic Table?
c) Why did Mendeleev leave some gaps in his Periodic Table?
Answers
Answer:
(a) Due to discovery of different elements, it was difficult to organize the information and properties of the elements, so there was a strong need to find some pattern in the properties of different elements so that they can be grouped together. That's why we classify elements.
(b) Atomic mass and similarity of chemical properties ( compounds formed by elements with oxygen and hydrogen )were the two criteria used by Mendeleev in his Periodic Table.
(c) Mendeleev went even further. He corrected the known atomic masses of some elements and he used the patterns in his table to predict the properties of the elements he thought must exist but had yet to be discovered. He left blank spaces in his chart as placeholders to represent those unknown elements.