Unit 1: Atoms
Scientists to Know CHADWICK THOMSON RUTHERFORD DEMOCRITUS BOHR HEISENBERG DALTON
The History of Discovering the Atom The Timeline of Discovery 1. Philosophical Era 2. Alchemical Era 3. Classical Era 4. Subatomic Era 5. Modern Era For later study The Intermediate Atomic Models 1. Uncuttable Model 2. --- 3. The Dalton Sphere Model 4. The Plumb Pudding Model The Planetary Model 5. The Quantum Model
Brainstorm about this era? THE PHILOSOPHICAL ERA (CIRCA 500~300BCE)
A time when logic ruled the land THE PHILOSOPHICAL ERA (CIRCA 500~300BCE)
Philosophical Era (Ancient Greece) o Their ideas were based on logic, without experimental support (as was common in that time) o Age of Thinking
Democritus (460-370 BCE) o Argued that matter was made of small, indivisible particles o Called the small particles atomos meaning that which cannot be divided o Believed properties of matter came from the properties of the atomos
Brainstorm about this era? ALCHEMICAL ERA (300 BCE ~ 1400CE)
The Dark Ages of Chemistry where early chemists had to work in secret and encode their findings for fear of persecution ALCHEMICAL ERA (300 BCE ~ 1400CE)
Alchemy o the closest thing to the study of chemistry for nearly two thousand years o Very mystical study and experimentation with the elements and what was perceived as magic o Study was illegal, findings hidden in code
Elements in Alchemy o Alchemists studied many different materials, and their properties, in order to find a way to turn lead into gold and achieve immortality
Brainstorm about this era? THE CLASSICAL ERA (1400CE 1887CE)
The printing press brings the widespread transfer and acquisition of knowledge THE CLASSICAL ERA (1400CE 1887CE)
John Dalton [really famous] (1766-1844) o Dalton returns to Democritus ideas in 1803 with four arguments I. All matter is made up of tiny particles II. III. IV. called atoms All atoms of a given element are identical to one another and different from atoms of other elements Atoms of two or more different elements combine to form compounds. A chemical reaction involves the rearrangement, separation, or combination of atoms. Atoms are never created nor destroyed during a chemical reaction. John Dalton
Brainstorm about this era? THE SUBATOMIC ERA (1897CE 1932CE)
The relatively quick discovery of things smaller than the once indivisible atom - EXPERIMENTAION THE SUBATOMIC ERA (1897CE 1932CE)
JJ Thomson o Use the cathode ray tube (glass chamber used to study electricity in gasses) to discover the electron.
J.J. Thompson English (1897) o Put magnetic fields near cathode rays (CRT) o Using three different arrangements of CRTs he was able to determine that the Cathode rays o Were streams of negatively charged particles o Those particles had very low mass-to-charge ratios
The First Subatomic Particle o Electrons one part of an atom with one negative charge o Since atoms were known to be electrically neutral, Thompson developed the plumb pudding model of the atom Positively (+) charged majority Negatively (-) Charged electrons
Ernest Rutherford New Zealander (1910) o Rutherford worked with radiation and had heard of Thompson s plumb pudding model o He wanted to use radiation to prove Thompson s model o With the help from Marie Curie, he shot alpha particles (+) at an ultra-thin piece of gold foil, with a Geiger counter on the other side Ernest Rutherford New Zealand Marie Curie Polish/ French
Rutherford s Results o Rutherford s results were not what he expected o Expected to have all alpha particles (+ charge) go straight through all of the atoms o Saw that occasionally an alpha particle would ricochet o Determined the positive charge of an atom must be held in a massive, centrally located, nucleus
The Second Subatomic Particle o After more experiments the second subatomic particle was formally named (1911) o Proton o Proton: The massive subatomic particle, within the nucleus of an atom, with a single positive charge
The Planetary Model (1911) o Earnest Rutherford took his idea of a nucleus, and the known electrons, to construct a new atomic model o Compact nucleus o With a positive center o The orbit of the electrons kept them from falling directly into the nucleus, just like planetary motion The Rutherford Model or The Planetary Model
The Third Subatomic Particle o Missing mass in the nucleus o James Chadwick determined that a another subatomic particle must be in the nucleus with the protons o Called this subatomic particle: neutron because it has NO charge. James Chadwick English
Brainstorm about this era? THE MODERN ERA (1900CE PRESENT)
The Quark Era starts in 1964, but that advance can be regarded as outside the realm of chemistry instead a part of nuclear physics THE MODERN ERA (1900CE PRESENT)
Bohr s Planetary Model of the Atom o integrated all known information into a new, math based, model of the atom o He kept electrons in energy levels or fixed orbits around the nucleus Niels Bohr Danish Physicist
The Modern (current) Atom Uncertainty Principle An electrons position, momentum, energy and time can never be known at the same time. Electrons are so small and relatively massless to measure it becomes impossible because any measuring technique causes it to change position / move. Werner Heisenberg Germany
What does it look like? Likely electron locations are now represented as clouds or orbitals (bubbles) Electron Clouds