S4.6.5 For the adult
The periodic table
How did one chemist predict elements that nobody had found yet?
What this chapter teaches
Mendeleev ordered the elements by atomic mass and left gaps for elements not yet found, then predicted their properties. Down group 1 reactivity rises, down group 7 it falls, and group 0 is unreactive because the outer shell is full.
Three questions to ask
There is no one right wording. Listen for the idea.
- Why did Mendeleev leave gaps in his table?
- Why does reactivity rise down group 1 but fall down group 7?
- Why are the noble gases unreactive?
After the chapter, the learner can
- Explain how Mendeleev arranged the elements and left gaps
- Describe trends in groups 1, 7 and 0
What they copy into their notebook
Mendeleev ordered by atomic mass, grouped by properties, swapped pairs and left gaps. Today: atomic number. Group 1 reacts more going down. Group 7 reacts less. Group 0 is unreactive, with a full outer shell.