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Unit 2 Part 1 History of the Atom Ms. Slack 6th Grade Science 2010 Lets Review… What is MATTER? • Matter is anything that has mass and takes up space! • What is NOT considered matter? • Light, Heat, Emotions, Thoughts • Everything around us is either classified as matter or energy. What Makes up Matter? • Democritus (460 BC – 370 BC): – Greek philosopher • believed that the universe was made up of empty space • bits of ‘stuff’ that were so small they could no longer be divided. – He called these tiny pieces atoms – Greek word which means ‘cannot be divided • Today an atom is defined as a small particle that makes up most types of matter. Other Early Contributions • Lavoisier was a French chemist who lived about 2000 years after Democritis. • Before Lavoisier, people thought that matter could appear and re-appear. Example? • Wood burning in a fireplace. Law of Conservation of Matter • Matter is not created or destroyed, it just changes form. Models of the Atom • Models are often used for things that are too small or too large to be observed. • In the case of atoms, scientists use large models to explain something that is too small to be looked at. • Atoms are so small they cannot be seen with the human eye. ATOMIC THEORY TIMELINE The Scientists and History of the Atomic Theory and Models John Dalton – early 1800’s His ideas included: 1. All matter was made up of one type of atom. 2. Atoms are too small to see with the “naked” eye. J.J. Thomson Model He discovered: 1. Atoms can be divided into “subatomic” or smaller particles. 2. Discovered the electron! Envisioned an atom to look like a: ball of chocolate chip cookie dough or a blueberry muffin Rutherford Model 1910 Rutherford discovered: 1. The atom is mostly empty space. 2. Has a positively charged center called the “nucleus”. 3. Called the positively charged parts “protons!” Chadwick Model – 1930’s A student of Rutherford’s he discovered: 1. The “neutron” – a particle in the nucleus with NO CHARGE! Modern Atomic Model The current model includes the following: 1. Electrons have energy levels – from low to high. 2. Electrons are found in a cloud “circling” around the nucleus.