[vicereine]

This seems like an easy question, but I'm a little confused. I'm supposed to answer why 18k gold jewelry would help people with nickel allergies vs 10k gold, and to explain using the reactivity of metals and the activity series. Now I assume that nickel is higher than gold on the activity series (it's not in the list they gave in my lesson book), but looking at the periodic table, gold is below nickel, and I thought reactivity of metals increases from top to bottom? So according to that, shouldn't gold be more reactive?

There's some other examples, like zinc being more reactive than chromium (http://en.wikipedia.org/wiki/Reactivity_series#A_reactivity_series_of_common_metals), even though reactivity increases from right to left for metals. So can someone explain the correlation between reactivity of metals and the activity series?

[Borek]

I thought reactivity of metals increases from top to bottom?

This is not a general rule, it allows only comparison of metals from the same group. It doesn't work for transition metals, in fact, it works best for the first two groups.