I was thinking about the general trend in metal activity (reactivity increases down a group and decreases across a period) when I started thinking about aluminum and how it has a lower first ionization energy than magnesium because its highest-energy electron is in a high-energy 3p orbital. Despite this, magnesium is the more active metal. Is this because activity measures the potential of the oxidation of Al t0 Al3+, not Al to Al+? Although it may not take much energy to remove the first electron from Al, oxidizing Al+ to Al3+ requires removing electrons from the lower energy 3s orbital, making the overall oxidation less favorable than the oxidation of Mg to Mg2+. Is this thinking correct?