Related topics: molecules , physical review letters , electrons , laser , absolute zero
Atom
hideThe atom is a basic unit of matter consisting 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 neutron). 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, forming a molecule. An atom containing an equal number of protons and electrons is electrically neutral, otherwise it has a positive or negative charge and is 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 determine the isotope of the element.
The name atom comes from the Greek ἄτομος/átomos, α-τεμνω, which means uncuttable, something that cannot be divided further. The concept of an atom as an indivisible component of matter was first proposed by early Indian and Greek philosophers. In the 17th and 18th centuries, chemists provided a physical basis for this idea by showing that certain substances could not be further broken down by chemical methods. During the late 19th and early 20th centuries, physicists discovered subatomic components and structure inside the atom, thereby demonstrating that the 'atom' was divisible. The principles of quantum mechanics were used to successfully model the atom.
Relative to everyday experience, atoms are minuscule objects with proportionately tiny masses. Atoms can only be observed individually using special instruments such as the scanning tunneling microscope. Over 99.9% of an atom's mass is concentrated in the nucleus, with protons and neutrons having roughly equal mass. Each element has at least one isotope with unstable nuclei that can undergo radioactive decay. This can result in a transmutation that changes the number of protons or neutrons in a nucleus. Electrons that are bound to atoms possess a set of stable energy levels, or orbitals, and can undergo transitions between them by absorbing or emitting photons that match the energy differences between the levels. The electrons determine the chemical properties of an element, and strongly influence an atom's magnetic properties.
For more information about Atom, read the full article at
Wikipedia.
This text uses material from Wikipedia and is available under the GNU Free Documentation License.
News tagged with atoms
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(PhysOrg.com) -- Drinking water can transmit a number of diseases, including typhoid, dysentery, cholera, and diarrhea, which can then spread explosively throughout an entire service area. To avoid this problem, drinking ...
Caltech scientists film photons with electrons
Dec 16, 2009 |
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(PhysOrg.com) -- Techniques recently invented by researchers at the California Institute of Technology -- which allow the real-time, real-space visualization of fleeting changes in the structure of nanoscale ...
New way to break some of the strongest chemical bonds
Dec 16, 2009 |
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(PhysOrg.com) -- Scientists at Cornell University in the U.S. have found a new way of breaking two of the strongest chemical bonds, at ambient temperature and pressure, and this breakthrough could lead to ...
Miracle light: Can lasers solve the energy crisis?
Dec 15, 2009 |
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Next year will mark the 50th birthday of the laser, one of the most productive and widely used mega-inventions of the last century. Scientists hope that 2010 also will see the launch of laser technology's greatest challenge: ...
Physicists lay the groundwork for cooler, faster computing
Dec 14, 2009 |
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University of Toronto quantum optics researchers Sajeev John and Xun Ma have discovered new behaviours of light within photonic crystals that could lead to faster optical information processing and compact computers that ...
New structure could produce efficient semiconductor laser sources
Dec 14, 2009 |
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(PhysOrg.com) -- University of Wisconsin-Madison researchers have achieved a nanoscale laser structure they anticipate will produce semiconductor lasers in the next two years that are more than twice as efficient ...
Super cool atom thermometer
Dec 07, 2009 |
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As physicists strive to cool atoms down to ever more frigid temperatures, they face the daunting task of developing new, reliable ways of measuring these extreme lows. Now a team of physicists has devised ...
Using lasers to cool and manipulate molecules
Dec 07, 2009 |
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(PhysOrg.com) -- "For years, we have been using laser cooling to trap and manipulate atoms," David DeMille tells PhysOrg.com. "This has been very useful for both basic science and many applications. Recent ...
Scientists take theoretical research on 'nasty' molecule to next level
Dec 04, 2009 |
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(PhysOrg.com) -- Some atoms don't always follow the rules. Take the beryllium dimer, a seemingly simple molecule made up of two atoms that University of Delaware physicists Krzysztof Szalewicz and Konrad Patkowski ...
A (nano-) window that washes itself?
Nanotechnology / Nanomaterials
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A coating on windows or solar panels that repels grime and dirt? Expanded battery storage capacities for the next electric car? New Tel Aviv University research, just published in Nature Nanotechnology, detail ...
Suzaku spies treasure trove of intergalactic metal
Dec 02, 2009 |
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Every cook knows the ingredients for making bread: flour, water, yeast, and time. But what chemical elements are in the recipe of our universe?
Researchers create 'synthetic magnetic fields' for neutral atoms
Dec 02, 2009 |
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(PhysOrg.com) -- Achieving an important new capability in ultracold atomic gases, researchers at the Joint Quantum Institute, a collaboration of the National Institute of Standards and Technology and the University ...
Researchers put a new spin on atomic musical chairs
Dec 02, 2009 |
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Researchers from the National Institute of Standards and Technology and the Naval Research Laboratory have developed a new way to introduce magnetic impurities in a semiconductor crystal by prodding it with ...
Fujitsu Develops Technology for Low-Temperature Full-Service Direct Formation of Graphene Transistors on Large-Scale Sub
Nov 27, 2009 |
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Fujitsu Laboratories today announced, as a world first, the development of a novel technology for forming graphene transistors directly on the entire surface of large-scale insulating substrates at low temperatures ...
Herschel takes a peek at the ingredients of the galaxies
Nov 27, 2009 |
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(PhysOrg.com) -- The European Space Agency has today released spectacular new observations from the Herschel Space Observatory, including the UK-led SPIRE instrument. Spectrometers on board all three Hershel ...
