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
Using lasers to cool and manipulate molecules
12 hours ago |
5 / 5 (6) |
0
(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 ...
How Perfect Can Graphene Be?
Nanotechnology / Nanomaterials
Oct 13, 2009 |
4.6 / 5 (30) |
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 ...
Atomtronic transistor and diode could advance quantum computing
Oct 09, 2009 |
4.6 / 5 (24) |
5
(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 ...
Buffer gas cooling could open up the field of ultracold physics
Sep 17, 2009 |
4.8 / 5 (22) |
2
(PhysOrg.com) -- "Scientists have been making Bose-Einstein Condensates [BECs] for nearly 15 years," Charlie Doret tells PhysOrg.com. "Essentially all BEC research to date, however, begins with laser cooling. Unfortunately, ...
Physicists Propose New Ultracold Scheme for Scalable Quantum Information Processing
Jun 03, 2009 |
4.1 / 5 (14) |
1
(PhysOrg.com) -- Since 1994, when Peter Shor famously showed that a quantum computer could factor large numbers exponentially faster than any current classical algorithm, physicists have been investigating ...
Engineering Carbon for Impressive Hydrogen Storage
Nanotechnology / Nanomaterials
May 22, 2009 |
4 / 5 (16) |
14
(PhysOrg.com) -- University of Missouri researchers recently showed how carbon nanostructures can be engineered to become excellent media for hydrogen storage, work that may be important for the advancement of hydrogen-energy ...
Is random lasing possible with a cold atom cloud?
May 18, 2009 |
4 / 5 (6) |
4
(PhysOrg.com) -- Random lasing, Robin Kaiser tells PhysOrg.com, is like standard lasing, with a little bit of a twist: “You don’t know the direction the photons will go, as you do with a more standard laser. This is becaus ...
Bouncing atoms may be the key to the future of gravimetry
Apr 27, 2009 |
4.4 / 5 (14) |
1
(PhysOrg.com) -- When studying cold atoms, scientists often use magnetic or optical traps to keep the atoms in place. However, in some cases experimentalists want to study free atoms, avoiding the effects of a trap. "One ...
New Research Promises Better Atomic Clocks
Apr 22, 2009 |
4.7 / 5 (9) |
1
(PhysOrg.com) -- The most accurate timekeepers in the world are atomic clocks, which tell time based on the absorption of a very specific and unchanging microwave frequency, which induces electrons in an atom to “jump” from ...
Study Yields Surprising New Insight into High-Temp Superconductors
Mar 17, 2009 |
4.8 / 5 (16) |
135
(PhysOrg.com) -- Recently, an international group of researchers discovered that the underlying mechanism producing high-temperature superconductivity in a widely studied class of copper-oxygen-based superconductors may be ...
Can alkaline earth metals be used in quantum computing?
Nov 14, 2008 |
4.9 / 5 (19) |
1
(PhysOrg.com) -- "There are a number of different proposals for quantum computing," Andrew Daley tells PhysOrg.com. "These include solid state or semiconductor as well as atomic and molecular systems. We are considering atomic ...
Current theories can't explain observed spin segregation
Oct 16, 2008 |
4.7 / 5 (79) |
10
(PhysOrg.com) -- Experiments with quantum systems sometimes yield surprising results. This is exactly what happened when John Thomas, a researcher at Duke University in Durham, North Carolina found out when he and his post ...
Long-Lasting Quantum Memory Leads to Long-Distance Quantum Communication
Oct 07, 2008 |
4.3 / 5 (54) |
6
(PhysOrg.com) -- Physicists have taken a step closer to realizing long-distance quantum communication, in which a quantum state is transferred from one location to another by becoming entangled with a traveling ...
Scientists take theoretical research on 'nasty' molecule to next level
Dec 04, 2009 |
4.4 / 5 (12) |
3
(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 ...
Researchers create 'synthetic magnetic fields' for neutral atoms
Dec 02, 2009 |
4.9 / 5 (15) |
2
(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 ...
