Summarizing Discovery of the Parts of the Atom

Discovery of the Parts of the Atom Summary

• Atoms are composed of negatively charged electrons, first proved to exist in cathode-ray-tube experiments, and a positively charged nucleus.
• All electrons are identical and have a charge-to-mass ratio of

  \(\cfrac{{q}_{e}}{{m}_{e}}=-\text{1.76}×{\text{10}}^{\text{11}}\phantom{\rule{0.25em}{0ex}}\text{C/kg.}\)

• The positive charge in the nuclei is carried by particles called protons, which have a charge-to-mass ratio of

  \(\cfrac{{q}_{p}}{{m}_{p}}=9\text{.}\text{57}×{\text{10}}^{7}\phantom{\rule{0.25em}{0ex}}\text{C/kg}\text{.}\)

• Mass of electron,

  \({m}_{e}=9\text{.}\text{11}×{\text{10}}^{-\text{31}}\phantom{\rule{0.25em}{0ex}}\text{kg}\text{.}\)

• Mass of proton,

  \({m}_{p}=1\text{.}\text{67}×{\text{10}}^{-\text{27}}\phantom{\rule{0.25em}{0ex}}\text{kg.}\)

• The planetary model of the atom pictures electrons orbiting the nucleus in the same way that planets orbit the sun.

Glossary

cathode-ray tube

a vacuum tube containing a source of electrons and a screen to view images

planetary model of the atom

the most familiar model or illustration of the structure of the atom