Before 1600, people studied substances to figure out how to do things such as turn lead into gold, but no one managed to do that. This was called alchemy. Alchemists separated the air into many parts and isolated the noble gases from it. They also processed special minerals from a mine in Sweden to get rare earth metals. Radioactivity was also discovered. Today chemists have discovered 118 different elements. Some are very common, like oxygen. Many are very rare and expensive, like platinum. Some cannot be found on earth and can only be made in labs, like rutherfordium.
Since the 1920s, the increased understanding of physics has changed chemists' theories about chemical reactions. With smaller and faster computers, chemists have built better tools for analyzing substances. These tools have been sent to study chemicals on Mars. Police also use those tools to study evidence from crime scenes.