- Online Text
- Unit Guide (PDF)
Section 1: Introduction
Figure 3-1. Image of a Gold Surface Taken with a Scanning Tunneling Microscope (STM)
Image of gold [Au (100)] surface created by using a scanning tunneling microscope (STM). The individual atoms are visible. Techniques such as STM allow scientists to learn about the inner structure of atoms and their components.
© Wikimedia Commons, Public Domain. Author: Erwinrossen, 2008.
Atoms are tiny: A million of them fit across a human hair. At this minuscule size, they are not visible to the human eye; the closest we can get to "seeing" individual atoms is with the scanning electron microscope, which can create images of matter at the atomic scale—outlining the shapes of individual atoms. Atomic scientists have found innovative ways of using observable phenomena to make inferences about the inner structure of the atom over the years. Gerd Binnig (born 1947) and Heinrich Rohrer (1933–2013), the Nobel Prize-winning inventors of the scanning tunneling microscope, allowed the atom to be visualized. (Figure 3-1) In this unit, we will follow the gradual change from considering the atom as a single indivisible particle to a later understanding of the atom composed of its constituent subatomic parts. This revolution in understanding the atom, which began in the late 19th century and continued through the first decades of the 20th century, is key to today's science and technology: electricity and electronics, nuclear power, atomic clocks, and many other inventions.
Before the late 19th century, chemists had no methods for probing the inner structure of the atom, so they assumed that the atom was indivisible—just as described by John Dalton early in the century. Gradually, scientists developed new techniques to probe the atom, and they used these phenomena to make inferences about the inner structure of the atom and its components. What we call "subatomic particles"—electrons, protons, and neutrons—were discovered in breakthrough investigations starting in the 1870s. The astonishing detail made visible by the scanning tunneling microscope is just one of the results of a long series of experiments that have culminated in the modern model of the atom, which continues to evolve today.