Astronomy 123 Basics   Bohr Model of the Atom 

The early concept of the hydrogen atom pictured the electron in a well-defined orbit circling a central proton.

The modern view of the hydrogen atom thinks of the electron as a "cloud" surrounding the proton in the nucleus.

Photons (the quantum of electromagnetic radiation) can be absorbed or emitted  by by an atom, boosting the electron to an excited state (on absorption) or bring the electron to a lower energy state (on emission).

More complex atoms:
• helium
• carbon

Molecules
A model of the carbon-monoxide (CO) molecule, as an example of the dynamics of molecules.

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