In 1982, the United States government changed the way it minted pennies. Before 1982, pennies were made of 95% copper and 5% tin. Now they are made of 97.5% zinc coated with copper. Because they weigh different amounts (have different masses) and are still the same item, they make a good model for studying isotopes. 4. What do the two kinds of pennies represent in this exercise?
5. How do the pennies differ? How do isotopes differ?
6. What do the pennies have in common? What do isotopes have in common?