Metal Reactivity

In todays reading I learned how copper metal, magnesium metal, and gold react with different elements. Copper metal reacts with oxygen gas in the air when heated to produce a black substance. Magnesium metal reacts with oxygen gas and when it is heated in the air it quickly burns. Gold does not react with any components in the air which makes it long-lasting. I also learned that when ranking the elements in order of chemical reactivity it is called an activity series.