are the heart of chemistry. People have always known that they exist. The Ancient Greeks were the firsts to speculate on the composition of matter. They thought that it was possible that individual particles made up matter. Later, in the Seventeenth Century, a German chemist named George Ernst Stahl was the first to speak of chemical reaction, specifically, combustion. He said that a substance called phlogiston escaped into the air from all substances during combustion. He said that a burning candle would go out if a candlesnuffer was put ov ....