The diagram represents an early periodic table first published in 1865 by G. New

Question

The diagram represents an early periodic table first published in 1865 by G. Newlands. It lists 62 element in atomic weight order arranged in 8 vertical columns called "octaves". a) One complete family of elements is missing from this table. Name this family (or group) of elements and briefly explain why it was not included. b) Li, Na, K, Rb and Cs are all listed in the same family. Briefly describe one property these five elements have in common. c) This table suggests that Cu should also be a member of the family listed in (b). Briefly describe one property of Cu which is not possessed by any of Li, Na, K, Rb or Cs. d) Uranium was misplaced because its atomic weight was wrongly calculated. The chloride of uranium, whose formula was thought to be UCl_2, was found to contain 62.9% uranium by weight. Calculate the atomic weight of uranium from these data. (These atomic weight of chlorine was known to be 35.5) e) What name is given to the zone of the periodic table on the Data Sheet which includes uranium?

Explanation / Answer

Let the weight of salt of uranium chloride taken = 100 grams

the amount of uranium = 62.9% , which means that amount of uranium in 100grams = 62.9grams

the amount of chlorine will be = 100-62.9 g = 37.1grams

the atomic weight of chlorine = 35.5grams / mole

so the moles of chlorine = 37.1grams / atomic weight = 37.1 / 35.5 = 1.05 moles

moles of uranium should be = half of moles of chlorine [as formula is UCl2]

so moles of uranium = 1.05 / 2 = 0.525 moles

moles = mass / atomic weight

atomic weight = Mass / moles = 62.9 / 0.525 = 119.81 g / moles

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