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
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News tagged with atomic structure
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(PhysOrg.com) -- Just a few decades ago, scientists believed that all ordered matter consists of self-repeating building blocks -- atoms, ions or molecules. In this view, the ordinary solids of everyday life ...
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Rice University scientists have won a $1.5 million grant from the National Institutes of Health to scrutinize the influenza A virus for clues that could lead to more effective antiviral drugs. Strains of influenza A include ...
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Oct 15, 2009 |
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By discovering the atomic structure of a key human enzyme, researchers at The University of Texas at Austin have pointed the way toward designing anti-HIV drugs with far less toxic side effects.
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(PhysOrg.com) -- Researchers have overcome a major obstacle in efforts to use tiny structures called carbon nanotubes to create a new class of electronics that would be faster and smaller than conventional ...
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(PhysOrg.com) -- John Spence, a physicist at Arizona State University, is a longtime user of the Advanced Light Source at Lawrence Berkeley National Laboratory, where he has contributed to major advances in lensless imaging. ...
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John Spence, a physicist at Arizona State University, is a longtime user of the Advanced Light Source at Lawrence Berkeley National Laboratory, where he has contributed to major advances in lensless imaging. ...
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(PhysOrg.com) -- The largest representation ever created of the atomic structure of diamond will be brought to the West End on Tuesday for public exhibition. The sculpture is one of three works of science art portraying carbon ...
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Proteins, the work-horse molecules necessary for virtually every human action from breathing to thinking, have proved an almost ghostly presence, daring scientists to fully grasp their structure and behavior. Now, physicists ...
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Scientists at the University of Liverpool and Durham University have developed a new material to further understanding of how superconductors could be used to transmit electricity to built-up areas and reduce global energy ...
New imaging technique reveals the atomic structure of nanocrystals
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(PhysOrg.com) -- A new imaging technique developed by researchers at the University of Illinois overcomes the limit of diffraction and can reveal the atomic structure of a single nanocrystal with a resolution ...
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(PhysOrg.com) -- IBM Research scientists, in collaboration with the Center for Probing the Nanoscale at Stanford University, have demonstrated magnetic resonance imaging (MRI) with volume resolution 100 million ...
True properties of carbon nanotubes measured
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For more than 15 years, carbon nanotubes (CNTs) have been the flagship material of nanotechnology. Researchers have conceived applications for nanotubes ranging from microelectronic devices to cancer therapy. Their atomic ...
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