Study GuideChemistry–Elements1. Discovery and Similarity1.1How Chemistry Began: Discovering ElementsModern chemistry began in the18th century, when scientists tried to understand what substancesare really made of. They studied how materials break down when heated or when electricity is passedthrough them.In1774, an English scientist namedJoseph Priestleymade an important discovery. When he heateda red powder calledmercuric oxide, it broke apart into:•aliquid metal(mercury), and•acolorless gasthat helped things burn.This gas was later namedoxygen.Scientists found that many substances can be broken down into simpler parts using heat or electricity.However, some substancescannot be broken down any further, no matter how much energy isused. These simplest substances are calledchemical elements. They are the basic building blocksof all matter.1.2How Many Elements Are There?In1789, the French chemistAntoine Lavoisierpublished one of the first lists of elements. At thattime, only33 elementswere known—and some of them turned out to be incorrect.By1930, careful work by many chemists increased the number of naturally occurring elements to90.Later, scientists working in high-energy laboratories created about20 additional elements. Theseelements areradioactive and unstable, and they do not occur naturally on Earth, although they arelikely formed in the hot centers of some stars.Today, the total number of known elements has reached112, and the list may continue to grow.The good news for students is thatonly about 40 elementsare important for basic chemistry.Preview Mode
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