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DEVELOPING THE ATOMIC THEORY Text 5.1: Page170-175 Agenda 1. 2. 3. 4. 5. Just How Small is an Atom? Developing Atomic Theory Modern Model Check & Reflect Assignment – Timeline of the Development of Atomic Theory Learning Goals By the end of the class, we should be able to Describe how the model of the atom has changed over time Describe the structure of the atom according to modern atomic theory Calculate the number of protons, neutrons and electrons in an atom based on the periodic table Minds On: Just How Small is an Atom? Development of Atomic Theory Philosophers of Ancient Greece reasoned there were 4 basic forms of matter Fire, Water, Earth and Air Development of Atomic Theory In ancient China they reasoned there were 5 basic forms of matter Fire, water, wood, metal and earth Development of Atomic Theory 440 BCE, Greek philosopher Democritus also hypothesized about the atom He thought that breaking down rock into powder would reduce it to tiny bits of matter that couldn’t be broken down any more Wasn’t popular at time because there was no experimental evidence to support his claim Modern Atomic Theory Rooted in the idea that an understanding of atoms and their structure can help us predict the properties of matter Began with John Dalton, who reconsidered the ancient idea that each different kind of element is composed of a different type of atom Dalton’s Atom Dalton’s theory stated: All matter is made of small, invisible particles called atoms Atoms of different elements have different properties Atoms of different elements can combine in specific ways to form new substances All atoms of an element are identical in proprieties such as size and mass Sound Familiar? Building Off Dalton… He had it right! All matter is made of small, invisible particles called atoms Atoms of different elements have different properties Atoms of different elements can combine in specific ways to form new substances All atoms of an element are identical in proprieties such as size and mass The Atom JJ Thompson researched the idea that atoms may be made of smaller parts that are charged Experiment included using electric currents in glass tubes called cathode ray tubes. The Atom JJ Thompson researched the idea that atoms may be made of smaller parts that are charged Through experimentation he determined atoms must be made of both + and – charged pieces We now know these to be electrons (-) and protons (+) The Atom Ernest Rutherford expanded on the idea of the size of the parts of the atom He calculated through experimentation that there was a tiny nucleus in the center of orbiting electrons Finishing Touches James Chadwick suggested in the nucleus also contained neutral particles Now known as neutrons Niels Bohr suggested electrons traveled in shells or energy levels With each shells having a specific number of electrons in them Also now sometimes described as “electron clouds” So What’s the Big Picture? So What’s the Big Picture? More Info on the Atom Note: Atomic Mass= # Protons + # Neutrons Check & Reflect Skim & Scan Chapter 5.1 Complete questions 1-6 on page 175 ‘Learning Checkpoint’. Answer in complete sentences in your notebook. Assignment - TimeToast Create a timeline of the development of the atomic theory. Include pictures, text, and info on two scientists per time period. Use p.g. 176 to help you…