Earth Sciences 1023A/B Lecture Notes - Lecture 2: Subatomic Particle, Relative Atomic Mass, Atomic Number
1 Mar 2015
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In the 5th century b. c. , greek philosophers (leucippus and democritus) proposed that matter was made up of tiny, indivisible particles in constant motion. Aristotle, however, did not accept the theory, and it was ignored for centuries. Modern atomic theory began with the publication in 1808 by british chemist and physicist john. Dalton of his experimental conclusions that: all atoms of one element have the same size and weight, and, atoms of elements unite chemically in simple numerical ratios to form compounds. H2o is a compound composed of two hydrogens and one oxygen. Element = a single or isolated group of particles composed of only one species of atoms. Atoms of all the same type define an element. In 1897, british physicist j. j. thomson (aka lord kelvin) discovered the electron, a negatively charged subatomic particle (i. e. , a particle smaller than the atom). For this work, he was awarded a nobel prize in 1906.
