7 Just a “thought experiment” DemocritusJust a “thought experiment”
8 John DaltonProposed the first atomic theory in 1803
9 Dalton’s Theory All elements are composed of indivisible particles. Atoms of the same element are the same.Atoms of different elements are different.Compounds are formed by joining atoms of two or more elements.
18 Bohr or “Planetary” Model (1913) Niels Bohr developed concept that electrons not moving randomlyElectrons moved around nucleus in energy levels (fixed orbits).Electrons move from between energy levels as atom gains/loses energy
19 Electron Cloud Model (Wave Model) (1926) Erwin Schrödinger develops equations to describe electron motion.Electron clouds, or orbitals, represent space where electron is likely to be.Nucleus also contains neutrons (no charge).
20 The Electron Cloud (Wave) Model Electrons travel in no definite path.The probable location of an electron is based on how much energy the electron has.
21 Are There Other Improvements? You Bet! Just wait and see!
22 10 Minutes Closing Activity With a partner, use your textbook:Look up today’s scientists in the index. Turn to the correct pages and read what the book says about each of these scientists.From your notes and the book, respond to the following:Explain the history of our understanding of the atom.What were the contributions/discoveries of these scientists?