Atomic theory is the description of atoms, the smallest units of elements. The scientific evidence for the existence of atoms and its even smaller constituents is so vast that most people now consider the existence of atoms to be a fact and not just a theory.
Dalton realized that if elements were made up of atoms, a different atom for each different element, atomic theory could explain Lavoisier's results. If two atoms of hydrogen always combined with one atom of oxygen, the resulting combination of atoms, called a molecule, would be water. Dalton published his explanation in 1803. This year is considered the beginning of modern atomic theory. S…
As more and more elements continued to be discovered, it became convenient to begin listing them in symbol form in a chart. In 1869, Dmitri Mendeleev listed the elements in order of increasing atomic weight and grouped elements that seemed to have similar chemical reactions. For example, lithium (Li), sodium (Na), and potassium (K) are all metallic elements that burst into flame if they get wet. S…
Early studies of radioactivity revealed that certain atomic nuclei were naturally radioactive. Some scientists wondered that if particles could come out of the nucleus, would it also be possible to force particles into the nucleus? In 1932, Cockcroft and Walton succeeded in building a particle accelerator, a device that could make streams of charged particles move faster and faster. These fast par…
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