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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 ?
These atoms hardly have an influence on this Rydberg electron's path.
Figure 5 shows the formation energy of two H and He atoms in W, and these two atoms are located in different sites.
When atoms bond, or join together, they form molecules.
The molecule is shaped like a hexagon (having six sides) and contains rings of carbon atoms. Six tripodlike feet support the structure.
A (--)-- atom is an atom that easily combines with other atoms.
"First, it shows how to use single atoms as sensors to obtain new information about the nanoscopic world--we name this approach Atom-Based Metrology," says Stroscio.
"Digital Atoms is extremely excited about having Hitachi Innovative Solutions Corporation as both a client and a partner," said Dave Weyher, Digital Atoms' president and CEO.
Once you had the ability to deal with atoms on an individual basis, you could invent this black box - a "meat machine" - that would physically transform common materials into fresh beef.
The goal was to make implementation a "non-event." The agreed-upon solution was to implement ATOMS sequentially, starting at the end of the assembly line.
It may be because the hydrogen particles are made up, not of single hydrogen atoms, but of combinations of two hydrogen atoms.
In like manner, when the atoms of carbon arrange themselves into a lattice and these lattices combine to form a crystal, the result is crystalline graphite, the type that forms during cast iron solidification.
Polzik of the Niels Bohr Institute in Copenhagen, and their colleagues teleported traits of a dim laser pulse, including the strength of its electromagnetic field, onto a cloud of 1 trillion cesium atoms.