Tellurium (127.6 u) is heavier than iodine (126.9 u).
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Tellurium ( u) is heavier than iodine ( u). Explain why Mendeleev placed tellurium before iodine, and how Moseley's later work showed that he was right.
Need a reminder? The key ideaShow
Dobereiner's triads: the atomic mass of the middle element of three similar elements is close to the mean of the other two. Newlands' law of octaves: every eighth element, in order of atomic mass, is like the first. Mendeleev's periodic law: the properties of the elements are a periodic function of their atomic masses; he left gaps and predicted unknown elements from their neighbours.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The properties. Iodine behaves like chlorine and bromine, and tellurium like sulfur and selenium. By mass, they would land in each other's families.
Step 2. Mendeleev's choice. He trusted the properties and swapped them, placing iodine with the halogens.
Step 3. Moseley. The atomic numbers are for tellurium and for iodine. In order of , tellurium comes first, as Mendeleev had placed it.
Answer: he followed the properties, and the atomic numbers later confirmed the order.
Discussion (0)
Log in to join the discussion.
Loading…