Scientists in the 19th and 20th century

  • Period: 322 to 384

    The Greeks: Aristotle

    -believed all objects were composed of a potential (matter) and a reality (form)
    -believed universe had no beginning or end, and that it was eternal
  • Period: 346 to 460

    The Greeks: Plato

    -used Empedocles element theory, and identified each elem. with reg. solid
    Fire=tetrahedron Air=octahedron
    Water=icosahedron Earth=cube
    -all properies of matter could be deduced through pure thought w/o experimentation
  • Period: 370 to 460

    The Greeks: Democritus

    -developed atomism to say that atoms were solid bodies that were infinite in #, size, and shape but not large enough to see w/naked eye
    -thought evrythng emitted thin films of atoms and that our bodies received sensations from these
  • Period: 420 to 480

    The Greeks: Leucippus

    -theorized that were 2 different elements: the "full" or "solid" and the "empty" or "void"
    -theory atomism: an infinite # of atoms exist and are responsible for special props. of matter
  • Period: 432 to 492

    The Greeks: Empodocles

    -believed all things were made of 4 elements; Earth, Fire, Water, and Air
    -conducted experiment to show that air existed and wasn't only empty space
    -reasoned, not experimentally, that light traveled in finite velocity
  • Jan 1, 1492

    Christopher Columbus

    -discovers the New World
  • Pilgrims

    -Pilgrims land at Plymouth Rock, Massachusetts
  • Period: to

    John Dalton

    -English chemist known for discovering Atomic Theory, but also discovered condition of Color Blindness
  • Period: to

    John Dalton

    -Law of Multiple Proportions: if 2 elements 2gether form more than 1 compound, then ratios of the masses of the 2nd element, which combine with a fixed mass of the 1st element, will be ratios of samll whole #s
    -Law of Definite Composition: compound always contains 2 or more elements combined in a definite proprtion by mass
    -Law of Conservation of Mass: mass of closed system completly isolated remain constant overtime. Created idea that mass can't be created/destroyed, but can be re-arranged.
  • War

    -American and French begin siege of Cornwallis at Yorktown
    -last battle of Revolutionary War
  • Period: to

    Hantaro Nagaoka

    -interested in kinetic theory of gases and stability of Saturn rings
    -presented idea at Tokyo society for mathematics/physics Dec. 1903 (announced discovery in British academic journal "philosophical magazine")
    -idea led to question of electrons losing nrg when they are constantly moving
    - in order to prove model, had to prove electrons were not losing nrg
    -Bohr released detailed atom model that agreed with him. Proved that electrons were not losing nrg as went around positively charged nucleus,
  • Period: to

    Robert Milikan

    -invented an Oil Drop experiment to study electrons (most famous for bcuz able to discover size of the charge of an electron)
    -Oil Drop: atomizer sprays fine mist of oil drops ino chamber. Some droplets then fall through to lower level. Let fall until reached terminal velocity. Measured terminal velocity/calculated mass of each drop of oil using a formula. Directed rays to bottom to apply charge to fallen drops = electrons attach to the drops. Electric field make droplets hang in mid-air.
  • Period: to

    Ernest Rutherford

    -studied under J.J. Thomson
    -dealt with radioactive elements
    -claimed all elements have half-lives and within a certain period of time these elements can turn into different stable elements
    -reported two types of rays: alpha and beta
    -discovered proton
    -1st to make nuclear reaction
  • Period: to

    Niels Bohr

    -1913, began study of atomic structure using Rutherford's model as a guide
    -created new model that could be used to show the physical and chemical properies of the atom (shows nrg levels and sublevels)
  • Period: to

    Erwin Schrodinger

    -QMM (Quantum Mechanical Model) is a model of atomic stucture based on mathematics and is accurate in locating where electrons are placed around the nucleus
    -studied the eigenvalue problems in the physics of continuous media which paved way for his future work
    -QMM determines allowed energies an electron can have and how to find the most probable location of an electron
    -QMM is based on a theory that states that matter has properties relating with waves called the quantum theory
  • Period: to

    Erwin Schrodinger

    -Heisenburg's Uncertainity Principle states that knowing the exact position and momentum, or speed of motion, of electrons at the same time is impossible
    -complex shapes of orbitals are used in the QMM which indicate the volumes of space where electrons would most likely be located
    -principal quantum #s are abbreviated with letter n, which label energy levels of an electron
    -greater the value of n, greater the distance the electrons are from the nucleus, and the greater the energy
  • Period: to

    Louis De Broglie

    -Einstein evaluated thesis "Research on the Theory Quanta", getting him a science degree
    -got theory based on Plancks theory equation, which is E=hv
    -believed that any moving particle/object had an associated wave
    -theory showed that light was considered both a particle and a wave
  • J.J. Thomson

    -achieved most brillant work of his life=oranginal study of cathode rays culminating in the discovery of the electron
  • Max Planck

    -Quantum Theory explains the world on the smalles scale by looking at the stucture/behavior of atom and of subatomic particles assuming that all energy comes in tiny invisible bundles
    -1900: E=h x f (higher energy levels--father from nucleus, to get higher--gain energy, ligth and radiation bundles called quanta, amount of energy measured in Joules (E), freguency in Hertz (f), H=planks constant in Joules per Hertz (j-second,j-s) Constant: 6.63 x 10^-34 j-s
  • Period: to

    Werner Heisenberg

    -1927, came to conclusion
    -states that you can not be completely certain of all characteristics (vector, speed, spin, mass) of a (sub) atomic particle at the same time, only probability of that being the case.
    -this is bcuz in the act of measuring some aspects of it you alter tje others, as you would need a measurement tool that did not interact w/(sub) atomic particle. Results in that you can never be certain of something if you measure it.
  • J.J. Thomson

    -suggested model of the atom as sphere of positive matter in which electrons are positioned by electrostatic forces. Tried estimate # of electrons in an atom from measurements of the scattering of light, X, beta, and gamma rays. Found ISOTOPES.
  • J,J, Thomson

    -believed structure of atom is something like raison bread (Raison Bread Theory). Assumed body of atom spherical object containing N electrons confined in homogenous jellylike substance but realatively massive positive charge distribution whose total charge cancels that of the N electrons. Model sometimes called Plum Pudding Model. Only prob with theory was fact that electrons are not in homogenous gelatinous mixtures.
  • Ernest Rutherford

    -discovered atomic nucleus, and developed the atomic model
  • World War I

    -beginning of War World War
  • Erwin Schrodinger

    -discovered his wave equation which came from a dissatisfaction with Bohr's orbit theory
  • James Chadwick

    -proved existence of Neutrons
    -smashed alpha particls into Be, and allowed radiation that was released to hit another target: paraffin wax. When the Be radiation hit H atoms in the wax, the atoms were sent into a detective chamber. In physics, known that omly particle having same mass as H atom could affect H in that manner (used radial to bomb H and N= atomic nucleus of N and H) (measured velocity of H and N nuclear)
  • Erwin Schrodinger

    -returned to University of Austria and studied problem of unifyinig gravitation and electromagnetism
  • John F. Kennedy

    -assassination of JFK