1913, improved rutherfords description of the atom, a miniature solar system in which the electrons revolved about the nucleus in prescribed orbits or energy levels.
late 1890's he described the atom as looking something like a plum pudding, where the plums represented negative electric charges (electrons) and the pudding was a shapeless mass of uniform positive electrification.
1911 - disproved thomson's model of the atom, introduced the nuclear model, which described the atom as containing a small, dense, positively charged center surrounded by a negative cloud of electrons. he called the center of the atom the nucleus
1808 - school teacher - elements could be classified according to integral values of atomic mass
an element was composed of identical atoms that reacted the same way, chemically
showed elements were arranged in order of increasing atomic mass, a periodic repetition of similar chemical properties occurred
what is an atom?
the smallest particle that has all the properties of an element
essentially empty space
what is the mass of a proton? neutron? electron?
proton - 1.673 x 10^-27 kg
neutron 1.675 x 10^-27 kg (slightly heavier)
electron 9.1 x 10^-31 kg