Chemistry Science 10 History of the Atom
Atomic Theory Answer the following questions How long has the Atomic Theory been around?How long has the Atomic Theory been around? Is the Atomic Theory the work of one scientist?Is the Atomic Theory the work of one scientist? Have there been many changes to the Atomic Theory?Have there been many changes to the Atomic Theory? Do you think we fully understand atomic behaviour?Do you think we fully understand atomic behaviour?
History of the Atom Began with Democritus Theory continually tested and refined through history until we have the current model
Democritus BC Greek Philosopher Pictured the atom as a solid sphere – hypothesised that there was a piece of matter that could no longer be divided in two No real science
John Dalton Hypothesised that there was a building block of matter Gave it the name of an atom Basically, he restated Democritus’s Theory based on scientific observation
John Dalton’s Theory Matter was composed of atoms Atoms of the same type all had similar mass A pure substance would contain the same type of atoms Compounds were different types of atoms combined together Chemical reactions were the rearranging of compounds
JJ Thompson Used electron beam directed at the atom to test behaviour Discovered that cathode rays were streams of electrons (negative particles)Discovered that cathode rays were streams of electrons (negative particles) Discovered there are both positive and negative particles
JJ Thompson’s Theory “Raisin-Bread” Model of the Atom Solid mass of positive charge (bread)Solid mass of positive charge (bread) Random electrons with negative charge throughout (raisins)Random electrons with negative charge throughout (raisins) Attempted to predict number of electrons using electrostatic forces
Ernest Rutherford Set out to test Thompson’s Model Used alpha particles (radioactive) directed at Gold Foil Proposed the Nuclear Model of the atom
Ernest Rutherford’s Model All atoms would have a positive nucleus 99.9% of atom’s mass99.9% of atom’s mass Only.1% of atom’s sizeOnly.1% of atom’s size Atoms would have orbiting electrons (like planets) Majority of the atom is empty space
Neils Bohr Tested planetary orbital model of atom Used Hydrogen spectra for analysis
Neils Bohr’s Model Discrete energy levels in which electron can exist Electrons can move between levels but never have a non- whole number energy level Quantization of energy
Quantum Mechanical Model No longer individual science Teams work together to solve problems Current model explains why the periodic table works
Quarks & Leptons Newest theory Quarks make up protons and neutrons Electrons are another type of matter called leptons Bosons create forces