Democritus (465BC)• Ancient Greeks came to believe all matter consisted of differing amounts of only 4 basic substances: earth, fire, water, and ether• Leucippus, teacher of Democritus, proposed matter was made of small particles• D. was first to use the word atomos: the smallest, indivisible part of matter
Back in the Iron Age….• Some elements are found in nature in a relatively pure form.• Sulfur, copper, gold,silver, and iron weremade into decorativeand useful objects.
The Alchemists (Dark Ages till the Renaissance)• Looked for the philosophers stone• thought they would find a way to turn Pb into Au• Newton dabbled in alchemy
The modern age begins• Henning Brand of Germany discovered phosphorus in 1669.• He collected 50buckets of urine,fermented it, andthen boiled off thewater.
Joseph Priestley• Discovers oxygen -1774 (at the same time as Lavoisier & Scheel)A “natural philosopher”Also credited withinventing soda water! (1733-1804)
• Law of conservation ofAntoine Lavoisier mass 1743-1794 • Discovers nitrogen gas, and that oxygen can be chemically separated from certain compounds • confirms law of definite proportions • father of modern chemistry • loses his head to the French Revolution
John Dalton 1766-1844• Father of modern Atomic Theory• thought atoms of an element were all identical and indivisible• compounds are formed from atoms of different elements
William Prout• Law of Definite Proportions1785-1850, a physicianDistilled HCl acid fromstomach juices, andsuggested that H is thefundamental particle
Dimitri Mendeleev (1834-1907) • Organizes the first periodic table • columns based on valence (reactivity) • position in a row based (mostly ) on atomic weight • left places in table for elements which were not yet discovered
Chemistry and Physics Join Forces The late 19th century through the 20thcentury
J J Thomson 1856-1940• Discovers the electron• Plum Pudding Model of the atom….• All the charged particles were randomly scattered like “plums in pudding”• did not know about neutrons• Nobel Prize 1906.Thompsons experiment to discover electrons (1897)
Wilhelm Roentgen 1845-1923 Discovered X-rays in 1895: his wife’s hand
Becquerel (1852-1908)In 1896, Henri Becquerel discovered thaturanium salts emitted rays that resembledX-rays in their penetrating power. Hedemonstrated that this radiation, unlikephosphorescence, did not depend on anexternal source of energy, but seemed toarise spontaneously from uranium itself.Becquerel had, in fact, discoveredradioactivity.
The Curies Pierre MarieMarie (1867-1934) - first woman to win a Nobel PrizePierre (1859-1906) – died in traffic accidentFormulated the theory of radioactivity while workingwith uranium; also discovered Polonium (named afterPoland) and radiumShe was a pioneer in using radiation in medicine, but wasunaware of the hazards of radiation.
Nikola Tesla 1856-1943 •Investigated X-rays •Got skin damage while experimenting
Ernest Rutherford (1871-1937) • Electrons are separated from the nucleus • nucleus has positive charge and the shells are negative • atoms are mostly empty space (1911) - the Gold foil experiment • Planetary model
Werner Heisenberg 1901-1976• Mathematical models with Schrodinger• The Uncertainty Principle• you can not know both the position and speed of an electron simultaneously
Heisenberg was a hydrogen filled nazi zeppelin that came to thisdisastrous end in the 1930’s.
Werner Heisenberg was a German physicist who, in his latetwenties, introduced what is known as the HeisenbergUncertainty Principle. This discovery shook the veryfoundation of subatomic physics.
Heisenberg’s principle states: For any moment in time, it is impossible to know the position and the momentum of a moving particle.Simply because the act of observing affects the behavior of the observed.
I’m sure you’re aware of some things that change their behaviordepending on how they are being observed, for example:
In the case of particles, the observer also affects the behavior ofthe observed. There are limits to how much we can know about aparticle at any given moment. Take this picture for example: Right now we can see the left side clearly. However, if we moved the magnifying glass,
Now we can see the right side clearly but can no longer see the left.
Imagine this:A microscope that can see electrons in orbit around the nucleusWe shoot ordinary light waves at the electron to find itsposition, but the wavelength is too long to be obstructed by the electron,so... We try gamma rays (shorter wavelength). The problem with this is that gamma rays have so much energy (high frequency), that upon contact, the electron is knocked out of orbit making impossible to know its
Albert Einstein 1879-1955• A “slow student” who revolutionized science and the world• Mass is a form of energy! E = mc2
Einstein didn’t like Quantum Mechanics• Einstein to Bohr, “God does not play dice with the universe”• Bohr, in response, “Who are you to be telling God what to do?”
Paul Dirac Further developed quantum theory from work of Heisenberg and Schrodinger Shared a Nobel Prize - 1933 Worked on Uranium enrichment during WW II
James Chadwick 1891-1974 • 1932 discovers the neutron • Explains isotopeshttp://www.nobel.se/physics/laureates/1935/chadwick-bio.html
Lise Meitner 1878-1968• Realized that some weight was lost during nuclear fission: E=mc2• Was part of the team that discovered nuclear fission in late 1930s
Enrico Fermi (1901-1954)• Emigrated from Fascist Italy in 1938 after winning Nobel Prize• Built first nuclear reactor – underneath the stadium at the University of Chicago - 1942
Arthur Compton 1892-1962Worked with Fermi on first reactorDemonstrated the particle aspect ofelectro-magnetic radiation:The Compton Scattering Effect
Glenn T. Seaborg 1912-1999• Responsible for the Actinide concept• Discovered ten elements: plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium, and 106 (named after him)
Radioactivity Three types• Alpha α – a He nucleus (2p+2n)• Beta β – an electron• Gamma γ – pure energy: EM waves
Penetration of Matter• Though the most massive and most energetic of radioactive emissions, the alpha particle is the shortest in range because of its strong interaction with matter. The electromagnetic gamma ray is extremely penetrating, even penetrating considerable thicknesses of concrete. The electron of beta radioactivity strongly interacts with matter and has a short range.