The atom is a basic unit of matter that consists 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 neutrons). 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 by chemical bonds based on the same force, forming a molecule. An atom containing an equal number of protons and electrons is electrically neutral, otherwise it is positively or negatively charged and is known as 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 determines the isotope of the element.

Chemical atoms, which in science now carry the simple name of "atom," are minuscule objects with diameters of a few tenths of a nanometer and tiny masses proportional to the volume implied by these dimensions. Atoms can only be observed individually using special instruments such as the scanning tunneling microscope. Over 99.94% 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 an unstable nucleus 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. The principles of quantum mechanics have been successfully used to model the observed properties of the atom.

Read more about Atom:  Etymology, Identification, Origin and Current State

Other articles related to "atom, atoms":

Atom (Ray Palmer) - Rogues Gallery
... As Chronos, he became the Atom's archnemesis and would in time became an expert in time travel and manipulation ... escapes from prison, the warden asks the Atom to discover how he achieved such a feat ... The Atom is able to recreate the escape and follows the villain to his hideout ...
Atom - Origin and Current State - Rare and Theoretical Forms
... most likely candidate for a stable superheavy atom, unbihexium, has 126 protons and 184 neutrons ... may offer an explanation.) As a result, no antimatter atoms have been discovered in nature ... Other exotic atoms have been created by replacing one of the protons, neutrons or electrons with other particles that have the same charge ...
Soluble Methane Monooxygenase (MMO) Systems - Proposed Catalytic Cycle and Mechanism
... starts with abstraction of the hydrogen atom from the substrate to form QH (the rate determining step), hydroxyl bridged compound Q and the free alkyl radical ... As the radical approaches, the H atom of the alkane leave the coplanar tricoordinate O environment and bends upward to create a tetrahedral tetracoordinate O environment ... On the other hand, it can start with a 2e- reduction process of bridging the O1 atom to give a water molecule, followed by elimination of the alcohol and regeneration of the enzyme ...
Radioactive Source - Changing Decay Rates
... and environmental effects which change the electronic structure of the atom, which in turn affects the presence of 1s and 2s electrons that participate in the decay process ... This relatively large effect is because beryllium is a small atom whose valence electrons are in 2s atomic orbitals, which are subject to electron capture in 7Be because (li. 187Os with a half-life of 41.6 × 109 y, but studies using fully ionised 187Re atoms (bare nuclei) have found that this can decrease to only 33 y ...
Atom (Ray Palmer) - Fictional Character Biography - Blackest Night
... Atom is then invited to visit undead Hawkman in order to discuss his heartache over his wife ... son of Al Pratt, the first hero to be called Atom ... close approximation of the tattered Sword of the Atom clothings he had used in the past ...

Famous quotes containing the word atom:

    The unleashed power of the atom has changed everything save our modes of thinking and we thus drift toward unparalleled catastrophe.
    Albert Einstein (1879–1955)

    The flame from the angel’s sword in the garden of Eden has been catalysed into the atom bomb; God’s thunderbolt became blunted, so man’s dunderbolt has become the steel star of destruction.
    Sean O’Casey (1884–1964)

    Thank God! none of my children have an atom of poetry in their composition!
    Augusta Leigh (1783–1851)