Problems Scientists		Problems
Scientists' Contributions
Scientist	Major Contributions
Avogadro	equal volumes of gases, at the same temperature and pressure, have the same number of molecules 6.023 E23  constant
Becquerel	uranium exposes sealed photographic film rays are given off by uranium and radium
Bohr	electrons move in a definite energy level around the nucleus quanta energy have ground and excited states
Chadwick	rays observed by Bothe in 1930 were a beam of uncharged particles:  neutrons
Dalton	first atomic theory based on data 1) all matter composed of atoms that cannot be further subdivided 2) atoms of the same element are identical 3) atoms join other atoms in simple whole numbers ratios to form compounds
Democritus	general theory world made of empty space and small, indivisible particles he called atoms different atoms for each material
Einstein	mass and energy are equivalent E=mc2
Gay-Lussac	volumes of reacting gases and gaseous products are in a ratio of small whole numbers, under constant temperature and pressure
Geiger and Marsden	gold foil  atom is mostly empty space
Lavoisier	combustion, matter cannot be created or destroyed
Millikan	oil drop experiment determined the charge of an electron
Moseley	modified atomic theory to include atomic number (up to that point mass considered)
Planck	electromagnetic energy is radiated in small packets called quanta 6.626 x 10-34 JHz
Proust	compounds always contain elements in the same ratio by mass:  law of definite proportions
Rutherford	predicted existence of neutron and demonstrated with Geiger-Marsden, nucleus is small heavy core in atom, the rest of which is empty space
Thomson	discovered electron and determined its charge-mass ration experimentally calculated the mass of the proton and discovered isotopes
Problems Scientists