While some elements such as gold and copper were identified over 5,000 years ago, scientists have not always understood (a) what elements are and (b) that they are the building blocks of compounds. Scientists around the world worked to discover and identify elements. The first recorded new discovery of an element was the discovery of phosphorus by Hennig Brand in 1669. Brand was trying to extract gold from human urine. He carried out many very smelly experiments. His hypothesis that urine is yellow because it contains gold was incorrect. However, he carried out his experiments, recorded his observations carefully and repeated his work to ensure his results were reliable. As a result he discovered the element phosphorus for the first time in recorded history. Scientific discoveries often start with an incorrect idea or hypothesis. Through testing that hypothesis by experimentation and observation it is changed over time and new, more accurate, theories develop. Questions 1. Why do you think so many scientific discoveries start from incorrect ideas or hypotheses? 2. How did Brand ensure his results were reliable? 3. Why is it important for scientists to publish their discoveries? 4. An important part of science is accepting that our first ideas are not always correct. What would happen if scientists ignored the evidence and held on to their incorrect opinions? 5. Research and present information on the discovery of phosphorus.
Chapter Summary
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A pure substance is one that is made up of only one type of particle. A mixture is a substance that is made up of two or more types of particle mingled together. An element is a pure substance that cannot be broken down into simpler substances by chemical means. Elements are made from just one type of atom. All known elements are listed on the Periodic Table. A compound is a pure substance made from two or more different elements that are chemically combined. A physical change is one in which no new substance is made. A chemical change causes new substances to form.
