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I'm a 9th grade physical science teacher, and we're currently learning periodic trends. This is the first chemistry my students have learned. One of our labs for this unit has to do with the relative reactivity of Al, Mg, and Ca in water and 1M HCl.

In past years, the lab has been fun, but not very educational, because students aren't connecting what they see (bubbles of hydrogen gas forming) with what they know about periodic trends. I'm trying to find a way to explain this that isn't overly-complicated, but also isn't terribly inaccurate.

My current plan is to explain that acids contain H+ ions, and during a reaction with a metal, electrons from the metal are given to the H+ ions, which then become H2 gas, which bubbles up out of the test tube. The lower the ionization energy and electronegativity, the easier or faster it is for the H+ to take the ions from the metal, which is why we see a faster and more violent reaction with the Ca, for example, than with the Mg.

Is this an accurate understanding? (Or at least accurate-enough understanding in a "lies-to-children" sort of way?) Is there any information that I'm missing or that would clarify the connection between the reaction and the properties of the metals? Or is there a better lab to demonstrate this concept altogether?

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    $\begingroup$ In this case it might be, but just talking about redox potential would be more accurate. Or just showing reactivity somewhat correlates with place in Periodic Table would maybe be less likely to bite them later on. BTW we're rather against lies-to-student, misconceptions, etc. around here. $\endgroup$
    – Mithoron
    Commented Feb 2 at 23:48
  • $\begingroup$ So you're saying that in this particular case, reactivity is caused by electronegativity, but that isn't always the case? $\endgroup$
    – Golden Eagle 1
    Commented Feb 3 at 2:03
  • $\begingroup$ By lies-to-children, I guess I meant things like teaching using Bohr models, because even though it's not actually accurate, it is a useful model up to a point. I always try to tell the students when we're simplifying things. $\endgroup$
    – Golden Eagle 1
    Commented Feb 3 at 2:05
  • $\begingroup$ Even with acids passivation can bring surprises, on the other hand sodium reacts especially violently. $\endgroup$
    – Mithoron
    Commented Feb 3 at 2:14
  • $\begingroup$ What age is 9th grade? Not everybody has the same education system $\endgroup$
    – Ian Bush
    Commented Feb 3 at 7:01

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