atom


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atom

 [at´om]
the smallest particle of an element that has all the properties of the element. adj., adj atom´ic.ƒThere are two main parts of an atom: the nucleus and the electron cloud. The nucleus is made up of protons, which carry a positive electrical charge, and (except in hydrogen) neutrons, which contain one proton and one electron and carry no electrical charge. The electron cloud is made up of particles called electrons, which carry a negative electrical charge and move in orbits or “shells” around the nucleus. Different atoms have different numbers of protons, neutrons, and electrons in their makeup.

In a chemical change, atoms do not break up but act as individual units. The chemical behavior of an atom is controlled by the number and spatial arrangement of electrons in orbit around the nucleus. The atoms of radioactive elements are very unstable and are capable of emitting nuclear particles in a stream or “ray;” these particles are called radiations.

The atomic number of an element is the number of free protons (those not in neutrons) in the nucleus; it is equal to the net positive charge of the nucleus. The atomic weight is the weight of an atom of a substance as compared with the weight of an atom of carbon-12, which is taken as 12.

at·om

(at'ŏm),
Formerly considered the ultimate particle of an element, believed to be as indivisible as its name indicates. Discovery of radioactivity demonstrated the existence of subatomic particles, notably protons, neutrons, and electrons, the first two making up most of the mass of the atomic nucleus. It is now known that subatomic particles are further classified into hadrons, leptons, and quarks.
[G. atomos, indivisible, uncut]

at·om

(at'ŏm)
Formerly considered the ultimate particle of an element, believed to be as indivisible as its name indicates. Discovery of radioactivity demonstrated the existence of subatomic particles, notably protons, neutrons, and electrons, the first two comprising most of the mass of the atomic nucleus. We now know that subatomic particles are further divisible into hadrons, leptons, and quarks.
[G. atomos, indivisible, uncut]

atom

the smallest particle of matter possessing the properties of an element.

at·om

(at'ŏm)
Formerly considered the ultimate particle of an element, discovery of radioactivity demonstrated the existence of subatomic particles, notably protons, neutrons, and electrons, the first two making up most of the mass of the atomic nucleus. Subatomic particles are now further classified into hadrons, leptons, and quarks.
[G. atomos, indivisible, uncut]
References in periodicals archive ?
As computer simulations show, this comparatively weak kind of interaction decreases the total energy of the system, and so a bond between the Rydberg atom and the other atoms inside the electronic orbit is created.
where E(X) is the total energy of the W supercell with a H or He atom, E([X.sub.2]) is the total energy of the supercell with two H or He atoms, and [E.sup.24.sub.W] is the total energy of 24 W atoms.
Each type of atom is identified by an atomic symbol.
They have found a way to gather up and move around atoms in bunches.
ATOMIC MASS equals the number of protons plus the number of neutrons (uncharged particles) found in a single atom of an element.
"We know when the atom jumps by monitoring the current passing through the atom, as well as 'listening' to these current changes--atom hops--by passing the current signal through a loud speaker," says Stroscio.
(There's already a Tezuka Osamu World Art Square Odaiba shop at the Aqua City shopping complex, 4th floor.) At press time, Tezuka Productions was still finalizing a listing of "Atom Dream Project" events to take place all around the country over the coming months.
How could there be an artificial atom? But Raymond Ashoori, a physicist at AT&T Bell Labs, had created one - an atom whose electron count was controllable by its human maker, from zero to 60.
Thus, the density of water vapor is nine times that of hydrogen at the same temperature, but since the oxygen atom has sixteen times the mass of the hydrogen atom, then the weight of the water particles is 16 + 1 + 1, or 18.
During solidification, the metal atoms attach themselves to the growing dendrites in evenly-spaced columns and rows so that the final structure may be pictured as many unit cells stacked one upon the other.
The artificial atom is actually a superconducting electrical circuit that the researchers make behave as an atom.
Atoms tend to stay put, but light is always on the move.