Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons (except in the case of hydrogen-1, which is the only stable nuclide with no neutrons). The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain bound to each other by chemical bonds based on the same force, forming a molecule. An atom containing an equal number of protons and electrons is electrically neutral, otherwise it is positively or negatively charged and is known as an ion. An atom is classified according to the number of protons and neutrons in its nucleus: the number of protons determines the chemical element, and the number of neutrons determines the isotope of the element.
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Famous quotes containing the word atom:
“The savages don’t have atom bombs.”
—Friedrich Dürrenmatt (1921–1990)
“The unleashed power of the atom has changed everything save our modes of thinking and we thus drift toward unparalleled catastrophe.”
—Albert Einstein (1879–1955)
“He bends to the order of the seasons, the weather, the soils and crops, as the sails of a ship bend to the wind. He represents continuous hard labor, year in, year out, and small gains. He is a slow person, timed to Nature, and not to city watches. He takes the pace of seasons, plants and chemistry. Nature never hurries: atom by atom, little by little, she achieves her work.”
—Ralph Waldo Emerson (1803–1882)