Unit 1: Atoms

1. Unit 1: Atoms

2. Scientists to Know … CHADWICK THOMSON RUTHERFORD DEMOCRITUS BOHR HEISENBERG DALTON

3. The History of Discovering the Atom Philosophical Era Alchemical Era Classical Era Subatomic Era Modern Era For later study… Uncuttable Model 2. --- 3. The Dalton Sphere Model 4. The Plumb Pudding Model The Planetary Model 5. The Quantum Model The Timeline of Discovery The Intermediate Atomic Models

4. A time when logic ruled the land… The Philosophical Era (Circa 500~300BCE)

5. Philosophical Era (Ancient Greece) • Their ideas were based on logic, without experimental support (as was common in that time)

6. Philosophical Era Democritus (460-370 BCE) • Argued that matter was made of small, indivisible particles • Called the small particles “atomos” meaning “that which cannot be divided” • Believed properties of matter came from the properties of the “atomos”

7. 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)

8. Alchemical Era Alchemy • the closest thing to the study of chemistry for nearly two thousand years • Very mystical study and experimentation with the elements and what was perceived as magic • Study was illegal, findings hidden in code

9. Alchemical Era Elements in Alchemy • Alchemists studied many different materials, and their properties, in order to find a way to turn lead into gold and achieve immortality

10. The printing press brings the widespread transfer and acquisition of knowledge The Classical Era (1400CE – 1887CE)

11. Classical Era John Dalton [really famous] (1766-1844) John Dalton The Atom • Dalton returns to Democritus’ ideas in 1803 with four arguments • All matter is made up of tiny particles 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.

12. The relatively quick discovery of things smaller than the once “indivisible” atom The Subatomic Era (1897CE – 1932CE)

13. Subatomic Era Cathode Ray Tubes • Glass chambers used to study electricity in gasses • Glowing rays were observed in all gasses, and even gasless set-ups

14. Subatomic Era J.J. Thompson English (1897) • Put magnetic fields near cathode rays (CRT) • Using three different arrangements of CRTs he was able to determine that the Cathode rays… • Were streams of negatively charged particles • Those particles had very low mass-to-charge ratios

15. Subatomic Era The First Subatomic Particle Positively (+) charged majority Negatively (-) Charged electrons • With the combined work of Thompson and other scientists the first subatomic particle was established! • Electrons – one part of an atom with one negative charge • Since atoms were known to be electrically neutral, Thompson developed the plum pudding model of the atom

16. Subatomic Era Ernest Rutherford New Zealander (1910) Ernest Rutherford New Zealand Marie Curie Polish/ French • Rutherford worked with radiation and had heard of Thompson’s plumb pudding model • He wanted to use radiation to prove Thompson’s model • He set-up an alpha particle gun (with help from Marie Curie) to shoot at an ultra-thin piece of gold foil, with a Geiger counter on the other side

17. Subatomic Era Rutherford’s Results • Rutherford’s results were not what he expected • Expected to have all alpha particles go straight through all of the atoms • Saw that occasionally an alpha particle would ricochet • Determined the positive charge of an atom must be held in a massive, centrally located, “nucleus”

18. Subatomic Era The Second Subatomic Particle • After more experiments the second subatomic particle was formally named (1911) • Rutherford determined all atomic nuclei were made up of hydrogen nuclei • Hydrogen nuclei are called Protons • Proton: The massive subatomic particle, within the nucleus of an atom, with a single positive charge

19. Subatomic Era The Planetary Model (1911) The Rutherford Model or The Planetary Model • Earnest Rutherford took his idea of a nucleus, and the known electrons, to construct a new atomic model • Compact nucleus • With a positive • The orbit of the electrons kept them from falling directly into the nucleus, just like planetary motion

20. Subatomic Era The Third Subatomic Particle James Chadwick English • Electrons and Protons were identified as particles, but these alone could not fully describe atoms • The charge-to-mass ratio of atoms was not what they thought it should be • James Chadwick studied an unnamed form of radiation– he found it to be electrically neutral and about the mass of a proton • Including these particles in the nucleus of the atom solved their questions about charge-to-mass ratios

21. 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)

22. Modern Era Bohr’s Planetary Model of the Atom Niels Bohr Danish Physicist • integrated all known information into a new, mathematically based, model of the atom • He kept electrons in energy levels or fixed orbits around the nucleus

23. Modern Era The Modern (current) Atom • We don’t know any electron’s exact location or momentum • Uncertainty Principle • Electrons are likely to exist in some areas around a nucleus, and not in other areas • We can determine the locations where electrons are very probable to be found Werner Heisenberg Germany

24. Modern Era What does it look like? Electron Clouds Electron Bubbles Likely electron locations are now represented as clouds or orbitals (bubbles)