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.
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News tagged with atoms
Researchers invent new method for graphene growth
Nanotechnology / Nanomaterials
Nov 10, 2009 |
4.9 / 5 (20) |
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(PhysOrg.com) -- A Cornell research team has invented a simple way to make graphene electrical devices by growing the graphene directly onto a silicon wafer.
First Bose-Einstein condensation of strontium
Nov 09, 2009 |
4.8 / 5 (10) |
5
In an international first, scientists from the Institute of Quantum Optics and Quantum Information (IQOQI, Austria) produced a Bose-Einstein condensate of the alkaline-earth element strontium, thus narrowly ...
Quantum gas microscope offers glimpse of quirky ultracold atoms
Nov 04, 2009 |
4.6 / 5 (19) |
4
(PhysOrg.com) -- Physicists at Harvard University have created a quantum gas microscope that can be used to observe single atoms at temperatures so low the particles follow the rules of quantum mechanics, ...
Tailoring the optical dipole force for use on molecules
Oct 29, 2009 |
3.4 / 5 (5) |
1
(PhysOrg.com) -- "Scientists have been working with dipole fields for quite some time," Peter Barker tells PhysOrg.com. "However, most of the work is focused on very small particles, like atoms, or on larger particles, such a ...
New methods are changing old materials
Oct 28, 2009 |
4.4 / 5 (10) |
2
(PhysOrg.com) -- A company that makes steel for bearings used in heavy trucks had a big problem. The trucks travel through harsh, perilous environments such as Siberia, and an unexpected bearing failure on ...
Identifying Molecules in Infrared Could Lead to New Medicines
Oct 27, 2009 |
5 / 5 (3) |
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(PhysOrg.com) -- An interdisciplinary team of researchers has created a new, ultra-sensitive technique to analyze life-sustaining protein molecules. The technique may profoundly change the methodology of biomolecular ...
Researchers make key step towards turning methane gas into liquid fuel
Oct 22, 2009 |
3.5 / 5 (8) |
1
(PhysOrg.com) -- Researchers at the University of Washington and the University of North Carolina at Chapel Hill have taken an important step in converting methane gas to a liquid, potentially making it more useful as a fuel ...
Physicists Turn to Radio Dial for Finer Atomic Matchmaking
Oct 20, 2009 |
4.5 / 5 (4) |
1
(PhysOrg.com) -- Investigating mysterious data in ultracold gases of rubidium atoms, scientists at the Joint Quantum Institute of the National Institute of Standards and Technology and the University of Maryland ...
Galactic magnetic fields may control the boundaries of our solar system
Oct 16, 2009 |
4.7 / 5 (9) |
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The first all-sky maps developed by NASA's Interstellar Boundary Explorer (IBEX) spacecraft, the initial mission to examine the global interactions occurring at the edge of the solar system, suggest that the galac ...
Physicist wins Packard Fellowship
Oct 16, 2009 |
2.3 / 5 (3) |
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(PhysOrg.com) -- MIT physicist Pablo Jarillo-Herrero has won a 2009 David and Lucile Packard Fellowship, an award he will use to study a new class of materials that could have applications in the semiconductor ...
Graphene: Unravelling the secrets of a magic material
Nanotechnology / Nanomaterials
Oct 15, 2009 |
4.8 / 5 (12) |
8
UCL researchers are helping to unlock the secrets of a material that could ultimately be used in a new generation of electronic devices.
Physicists discover novel electronic properties in two-dimensional carbon structure
Oct 14, 2009 |
4.8 / 5 (11) |
1
Rutgers researchers have discovered novel electronic properties in two-dimensional sheets of carbon atoms called graphene that could one day be the heart of speedy and powerful electronic devices.
How Perfect Can Graphene Be?
Nanotechnology / Nanomaterials
Oct 13, 2009 |
4.6 / 5 (29) |
5
(PhysOrg.com) -- Physicists have investigated the purest graphene to date, and have found that the material possesses unprecedented high electronic quality. The discovery has raised the bar for this relatively ...
Growing geodesic carbon nanodomes
Oct 12, 2009 |
5 / 5 (4) |
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Researchers analyzing the assembly of graphene (sheets of carbon only one atom thick) on a surface of iridium have found that the sheets grow by first forming tiny carbon domes. The discovery offers new insight ...
Atomtronic transistor and diode could advance quantum computing
Oct 09, 2009 |
4.6 / 5 (24) |
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(PhysOrg.com) -- What if atoms could be used to perform the functions currently the province of electronic devices? The goal of atomtronics is to do just that by creating analogues to the common items found in electronic ...
