Atomic Theory Timeline - Project, Slides of Chemistry

Download Atomic Theory Timeline - Project and more Slides Chemistry in PDF only on Docsity! The atomic theory has changed over time as new technologies have become available. Atomic Theory Timeline Scientific knowledge builds on past research and experimentation. Democritus 400 B.C. Information Atomic Model Analogy Democritus, a philosopher in ancient Greece, began the search for a description of matter. He questioned whether matter could be divided into smaller and smaller pieces forever until eventually the smallest possible piece would be obtained. He believed that the smallest possible piece of matter was indivisible. He named the smallest piece of matter “atomos,” meaning “not to be cut.” To Democritus, atoms were small, hard particles that were all made of the same material, but were formed into different shapes and sizes. Legos Thomson 1897 Information Atomic Model Analogy In 1897, the English scientist named J.J. Thomson provided the first hint that an atom is made of even smaller particles. He discovered the presence of a negative particle in the atom – the electron. He proposed a model of the atom that is sometimes called the “Plum Pudding” model. His theory was that atoms are made from a positively charged substance with negatively charged electrons scattered about, like raisins in a pudding or chocolate chips in a cookie. Chocolate Chip Cookie Rutherford 1908 Information Atomic Model Analogy In 1908, the English physicist Ernest Rutherford performed an experiment using positively charged particles fired at gold foil. Through his experiment, he proved that atoms are not a “pudding” filled with a positively charged material. He theorized that atoms have a small, dense, positively charged center, which he called the “nucleus”. He said that nucleus is tiny compared to the atom as a whole, because the atom is mostly open space! He concluded that the negatively charged particles are scattered outside the nucleus at a distance. Cherry with a Pit Bohr 1913 Information Atomic Model Analogy In 1913, the Danish scientist Niels Bohr proposed an improvement. He built on the concept that the mass of an atom is contained mostly in the nucleus. He also theorized that electrons move in definite orbits around the nucleus, much like planets circle the sun. These orbits, or energy levels, are located at certain distances from the nucleus. Solar System