Hydrogen is placed at the top of group 1, but it is hard to place.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Hydrogen is placed at the top of group 1, but it is hard to place. Give two reasons to put it in group 1, and two reasons to put it in group 17.
Need a reminder? The key ideaShow
The position predicts the valency, the formulas, the reactivity and the nature of an element. A property in the middle of a group can be estimated as the average of its two neighbours, but only roughly.
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. Group 1. It has one outer electron, and it forms the ion , as sodium forms .
Step 2. Group 17. It needs one more electron to fill its shell, and it forms molecules of two atoms, , like .
Answer: group 1: one outer electron, forms . Group 17: one short of a full shell, forms .
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