Presentation on theme: "History of Atomic Theory"— Presentation transcript:
1 History of Atomic Theory Review of In-Class ResearchTuesday, September 15th, 2015
2 Ancient Philosophy § Who: Aristotle, Democritus, Leucippus § When: More than 2000 years agoears ago§ Where: Greece§ What: Aristotle believed in 4 elements: Earth, Air, Fire, and Water. Democritus believed that matter was made of small particles he named “atomos”.§ Why: Aristotle and Democritus used observation and inference to explain the existence of everything.
3 Like to the Greeks (Democritus)? What did an Atom LookLike to the Greeks (Democritus)?This was Democritus’ atomic model. It was simply a round sphere with no electrons, protons, or neutrons. Democritus created the first atomic model. His contribution helped people to understand the idea of an atom, then other scientists looked further into the science of the atom and its general makeup.
4 Dalton’s Particle Theory of Matter Who: John DaltonWhen: 1808Where: EnglandWhat: Described atoms as tiny particles that could not be divided. Thought each element was made of its own kind of atom.Why: Building on the ideas of Democritus in ancient Greece.What did an Atom look like to Dalton?
5 Discovery of Electrons Who: J. J. ThomsonWhen: 1897Where: EnglandWhat: Thomson discovered that electrons were smaller particles of an atom and were negatively charged.Why: Thomson knew atoms were neutrally charged, but couldn’t find the positive particle.
6 Thomson’s Cathode Ray Tube Understanding Thomson’s Experiment
7 What did an Atom look like to Thomson? Bunch of negative charged particles (raisins) in a sphere of positive charge (plum pudding)
8 Discovery of Nucleus Who: Ernest Rutherford When: 1911 Where: England What: Conducted an experimentthat resulted in discovery of atom’s nucleus.Decided that the atoms were mostly emptyspace, but had a dense central core.Why: He knew that atoms had positive and negative particles, but could not decide how they were arranged.
11 Bohr’s Model of the Atom Who: Niels BohrWhen: 1913Where: EnglandWhat: Proposed that electrons traveled in fixed paths around the nucleus. Scientists still use the Bohr model.Why: Bohr was trying to show why each element emitted its own unique frequency of energy as electrons jumped orbits.
13 Our Current Model - The Electron Cloud - Bohr said electrons orbit the nucleus (like the planets around the Sun)- The electron cloud model says that we can't know exactly where an electron is at any given time, but theelectrons are more likelyto be in specific areas.
14 Our Current Model - The Electron Cloud - Bohr assigned electrons to different shells- Using quantum mechanics, the electron cloud model assigns electrons to different atomic orbitals. ** These are not all spheres
15 For the quiz/testYou should know the main scientists and their experiments/contributions.You should be able to draw their models of the atom and explain differences.