The atoms bond because there is a strong enough attraction in both directions and room for the electrons in the outer energy level of the atoms. When two hydrogen atoms and an oxygen atom get close ...

Thus when an atom absorbs or gives off energy (as in light or heat), the electron jumps to higher ... of light emitted by real hydrogen atoms. Bohr's theory that electrons existed in set orbits ...

The picture shows a close-up of one carbon atom. A hydrogen atom has one proton as the nucleus and one electron in the region outside the nucleus. The electron and proton are attracted to each other.