(a) Why do we classify elements?
(b) What were the two criteria used by Mendeleev to classify the elements in his periodic table?
(c) Why did Mendeleev leave some gaps in his periodic table?
(d) In Mendeleev's periodic table, why was there no mention of noble gases like helium, neon and argon?
(e) Would you place the two isotopes of chlorine, CI-35 and CI-37 in different slots because of their different atomic masses or in the same slot because their chemical properties are the same? Justify your answer.
Answers
Answer:
1)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.
2)The two certeria used by Mendeleev to classify the elements in his periodic table are: Atomic mass: elements are arranged in the order of increasing atomic masses. The formulae of the hydrides and the oxides formed by the various elements.
3)Mendeleev left gaps in his table to place elements not known at the time. By looking at the chemical properties and physical properties of the elements next to a gap, he could also predict the properties of these undiscovered elements. ... The element germanium was discovered later.
4)There was no mention of noble gases like helium, neon, and argon as they were not known at that time and were discovered much later. Since they are very inert gases, it was difficult to detect them with the primitive technology.