Would you place the two isotopes of chlorine, Cl-35 and Cl-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.

(a) Why do we classify elements? (b) What were the two criteria used by Mendeleev to classifiy 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, Cl-35 and Cl-27 in different slots because of their different atomic masses or in the same slot because theri chemical properties are the same? Justify your answer.

Atoms of two different elements are represented in the following diagram. Do these elements belong to the same group ? Justify your answer.

Why are isotopes of an element having different atomic masses placed at the same position in the Periodic Table?

Do different species of plant a growing in the same area show the same rate of tranpiration at a particular time ? Justify your answer.

Would you expect the first ionisation enthalpies for two isotopes of the same element to be the same or different? Justify your answer.