3 Ancient Philosophy Who: Democritus When: 400 B.C. Where: Greece What: Democritus believed that matter was made of small, indivisible particles he named “atoms”.Why: Democritus used observation and inference to explain the existence of everything.
4 “What you see is what you get.” At this time in history, science was:“What you see is what you get.”
6 Particle Theory Who: John Dalton When: 1803-1808 Where: England What: Described atoms as tiny particles that could not be divided (like billiard balls). Thought each atom of a given substance were identical.Why: Building on the ideas of Democritus in ancient Greece.Solid Spheres
7 Dalton’s Atomic Theory 1. All matter is composed of atoms 2. Atoms of same element are identical AND atoms of different elements are different 3. Atoms can’t be divided, created, or destroyed 4. Atoms of different elements combine to form compounds 5. In chemical reactions, atoms are combined, separated, or rearranged.
8 Does Dalton’s Atomic Theory Still Hold True Today???
9 Dalton didn’t know about isotopes Dalton didn’t know about isotopes. All identical atoms are NOT identical because we have different forms of them.Dalton didn’t know about parts of an atom! They CAN be divided into parts! We now know about proton, neutron, electrons, nucleus etc.
11 Discovery of Electrons Who: J. J. ThompsonWhen: 1904Where: EnglandWhat: Thompson used Cathode Rays to discover that electrons were smaller particles of an atom and were negatively charged.Why: theorized that the neutral particles called atoms have no charge because it is actually made up of two types of charged parts, one positive and one negative so the charge cancels out.
12 J.J. Thompson’s Plum Pudding Model NOTICE:NO nucleus!
13 Honors Chemistry: Atomic Theory Cathode Ray TubeJ.J. ThomsonDiscovered mass/charge of e-1906 Nobel Prize in Physics
15 Atomic Structure I Who: Ernest Rutherford When: 1909 Where: England What: Conducted a Gold Foil experiment to isolate the positive particles in an atom. Decided that the atoms were mostly empty space, but had a dense central core.Why: He knew that atoms had positive and negative particles, but could not decide how they were arranged.
16 Rutherford’s Results: Most of the large positive particles went straight through! (hit nothing)2. Some were totally bounced back, hit something very hard and dense.3. Some were deflected. In entirely different directions from each other!Meant there were positiveAND negative particles/areasinside!
17 The Nuclear Model: Extremely small, dense and positively charged nucleus surrounded by emptyspace sparsely occupied by electrons.
19 Atomic Structure II Who: Niels Bohr When: 1913 Where: England What: Proposed that electrons traveled in fixed paths around the nucleus. Scientists still use the Bohr model to show the number of electrons in each orbit around the nucleus.Why: Bohr was trying to show why the negative electrons were not sucked into the nucleus of the atom.
20 Planetary ModelElectrons travel around the nucleus in orbits of that have a set energy levelScientists cannot predict where they will be at any given moment.