 | By the beginning of the 20th century, scientists knew there were elements or different kinds of atoms, but they did not know the structure of the atom.
In a few short decades, the main properties of the atom and its elementary particles were discovered.
Fundamental to these discoveries was learning about the connection between the changes in atomic energy levels and the emission or absorption of photons by the atom.
These scientific advances indicated, however, that there were very strange properties in the quantum theory underlying the atom:
the probabilistic nature of the atom, the uncertainty principle, wave–particle duality of matter, and particles that carry momentum but no mass.
These ideas were so unexpected and weird that even Albert Einstein resisted them at first. In this chapter you will learn about our modern understanding of the atom and the quantum theory.
|  | | By the end of this chapter you should be able to
|  | describe the structure of the atom and solve isotope problems;
| | describe evidence for a dense and positively charged nucleus;
| | describe evidence for the Bohr model of the hydrogen atom;
| | describe emission and absorption of a photon by an atom and calculate the photon’s properties;
| | describe how to identify elements using spectroscopy; and
| | summarize the main features of the quantum theory, including quantization, uncertainty, probability, and wave–particle duality.
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|  | 26A: Rutherford scattering experiment
26B: Energy levels of the hydrogen atom
26C: Phosphorescence
26D: Identifying elements using spectroscopy
Design project: Infrared pulse monitor
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