EasyChemistryHigh School (9–10)GeneralThe Periodic Table › Development of the Periodic TableConceptualBoard Exam
Mendeleev left gaps in his table. Why was that important? …
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Mendeleev left gaps in his table. Why was that important? Name one element that later filled a gap, and say what Mendeleev had called it.
Need a reminder? The key ideaShow
Mendeleev arranged the elements by atomic mass, in groups of similar properties. He left gaps and predicted the missing elements, such as eka-aluminium (gallium) and eka-silicon (germanium). Error of a prediction .
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. Why it mattered. He refused to force elements into places where their properties did not fit. The gaps said that elements were still unknown.
Step 2. Predictions. He described the missing elements, so the table could be tested.
Step 3. An example. Gallium filled the gap he called eka-aluminium, and it matched his description.
Answer: the gaps made testable predictions; gallium, which he called eka-aluminium.
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