The Modern View of Matter

-in 1860s it was thought there were 80 elements-organized into a table (the Periodic Table) by Dimitri Mendeleev

-Atoms were thought indivisable in the 1800s. -Each element was made of a different atom-Not sure then why each acted so differently-Perhaps there are smaller objects than atoms

-Discovered the electron in 1897 in Cambridge, England-More than 100 years later, it is still believed to be a fundamental particle, it cannot be broken down.

-Thompson made a partical accelerator-particals accelerated using magnetic plates-The particals would hit a screen which would glow when a partical hit it-He varied the voltage to bend the electron stream-He was able to deduce the mass of the particles from this-the smallest were approximately 2000 times smaller than a hydrogen atom, the smallest known particle at that time.-Thompson had discovered the electron

-Thompson thought of the "raison bun" model-He believed the electrons were imbedded in the positive mass of the atom-This was later proven to be wrong by one of his students

-In 1911, Rutherford discovered the atomic nucleus -Fired alpha particles at a piece of gold foil-used the decay of radioactive particles to produce a beam (through a hole in a block of lead)-most passed right through but 1 in 8000 bounced back-they had hit something small and dense-this proved there was a mass at the centre with electrons orbitting it-most of matter is actually empty space-if an apple were the nucleus, electrons could be up to 1km away

-we know now it isn't quite correct-we cannot say exactly where an electon will be (ie. not in a specific orbit)-quantum mechanics tells us they will be in distinct shells

-with further experiments, Rutherford and James Chadwick discovered in 1932 that there are 2 particles in the nucleus of an atom-positive protons and neutral neutrons

-a test at the Stanford Linear Accelerator Centre in 1968 proved the existance of Quarks-used an electron beam to take a microgram of the proton-the three fundamental particles (quarks) were observed

-12 fundamental particles in 4 families-Up Quark-Down Quark-Electron-Electron Neutrino-The other families identicle but heavier

-Recreated in the Hadron Collider-it has a circumfrance of 27km and 2000 superconducting magnets at 1.9K-protons accelerated to 99.99999% the speed of light-they collide in 4 large detectors-pictures of the collision are taken at a rate of 600 million times a second-this will help us understand the nature of the universe

-1912 more subatomic particles were discovered-before it was believed that there were 3, protons, neutrons, electrons-cosmic rays were discovered-by the 1960s, more than 80 fundamental particles had been found

-Murray Gell-Mann simplified these 80 particles-He observed symetries between them-He found that protons, neutrons and all of the other 80 were made of the same 3 particles, Quarks

-forces are the agents of change-they are present everywhere-CERN (Switzerland) built a CMS Detector, the most expensive scientific equipement ever to study them

-there are four forces-nuclear forces, gravity and electromagnetism-Gravity is the weakest and can be ignored in subatomic studies-electromagnetism holds electrons in place

-Michel Faraday found that electricity and magnetism were manifestations of the same thing

-James Clark Maxwell found the true connection-unified them with mathmatics