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“Introduction to the Elements” Video Note-taking Guide Aristotle vs. Democritus views on matter in 400BC Aristotle- a Greek philosopher who thought… Everything is made up of 4 elements (earth, fire, air and water) Democritus- a Greek philosopher who thought… Everything was made of atoms o Atomos means… can’t be divided Whose idea is closer to what we believe today? Democritus Whose idea was widely accepted for ~2000 years? Aristotle Alchemists were early chemists whose mean focus was … to turn Pb to Au (change one element into another) Elements are … the building blocks of matter, basic substances that can’t be broken down by ordinary chemical changes Number of naturally occurring elements : 92 Number of elements: 112 All are listed on the … Periodic table (blue: man made black: natural) History of atomic theory 1808 John Dalton’s Atomic Theory based on Democritus’ early ideas 1. Tiny particles….. that could not be divided 2. Each element…. Has its own kind of atom Model is sometimes called the billiard ball model 1897 JJ Thomson discovered the first subatomic particle… electron Sketch his model think of it looking like a chocolate chip cookie 1911 Ernest Rutherford famous Gold Foil Experiment Most particles… passed right through the gold foil 4/10,000 particles… bounced back off the foil He concluded that … atoms are made mostly up of empty space with a tiny nucleus that has a positive charge Sketch his model think of it being kind of like the inside of a peach 1913 Niels Bohr model is called a planetary model because… electrons orbit the nucleus like planets orbit the sun Energy levels around the nucleus contain.. electrons Modern Atomic Theory Our current atomic model is … the electron cloud model It’s called the Electron Cloud model because… the electrons travel