What holds atoms together in molecules?

I understand that cations attract anions, and that's what holds ionic compounds together. What holds atoms together in molecules?

Molecules are held together by electrons shared between bonded atoms. For example, consider the formation of an H2 molecule from two separate hydrogen atoms:
covalent bond in H2
2 approaching
hydrogen atoms
(2 H)
a hydrogen molecule
As the two atoms approach, each nucleus begins to attract the other atom's electrons. The shared electrons spend much of their time wedged between the two nuclei (where they can be be as close as possible to both of the positive charges at once). The attraction of nuclei for shared electrons holds the atoms together. A molecule has formed.

Because of the wavelike nature of electrons, you really need quantum mechanics to accurately describe this process.

Author: Fred Senese senese@antoine.frostburg.edu

General Chemistry Online! What holds atoms together in molecules?

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Last Revised 08/17/15.URL: http://antoine.frostburg.edu/chem/senese/101/compounds/faq/print-covalent-bonding.shtml