Changes

[[Image:lighterstill.jpg]]

[[Image:lighterstill.jpg]]

[[Image:Helium_atom_QM200.jpg|right|frame|<center>This illustrates the [http://en.wikipedia.org/wiki/Nucleus nucleus] (pink) and the [http://en.wikipedia.org/wiki/Electron_cloud electron cloud] distribution (black) of the [http://en.wikipedia.org/wiki/Helium Helium] atom. The nucleus (upper right) is in reality spherically symmetric, although this is not always the case for more complicated nuclei.</center>]]

[[Image:Helium_atom_QM200.jpg|right|frame|<center>This illustrates the [https://en.wikipedia.org/wiki/Nucleus nucleus] (pink) and the [https://en.wikipedia.org/wiki/Electron_cloud electron cloud] distribution (black) of the [https://en.wikipedia.org/wiki/Helium Helium] atom. The nucleus (upper right) is in reality spherically symmetric, although this is not always the case for more complicated nuclei.</center>]]

==Origin==

==Origin==

[https://nordan.daynal.org/wiki/index.php?title=English#ca._1100-1500_.09THE_MIDDLE_ENGLISH_PERIOD Middle English], from [[Latin]] ''atomus'', from [[Greek]] ''atomos'', from ''atomos'' indivisible, from ''a''- + ''temnein'' to cut which means uncuttable, or indivisible, something that cannot be divided further.

[https://nordan.daynal.org/wiki/index.php?title=English#ca._1100-1500_.09THE_MIDDLE_ENGLISH_PERIOD Middle English], from [[Latin]] ''atomus'', from [[Greek]] ''atomos'', from ''atomos'' indivisible, from ''a''- + ''temnein'' to cut which means uncuttable, or indivisible, something that cannot be divided further.

*[http://en.wikipedia.org/wiki/15th_century 15th Century]

*[https://en.wikipedia.org/wiki/15th_century 15th Century]

==Definitions==

==Definitions==

*1:  one of the minute indivisible [[particles]] of which according to [[ancient]] [[materialism]] the universe is composed

*1:  one of the minute indivisible [[particles]] of which according to [[ancient]] [[materialism]] the universe is composed

*4:  the atom considered as a source of vast [[potential]] [[energy]]  

*4:  the atom considered as a source of vast [[potential]] [[energy]]  

==Description==

==Description==

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 [http://en.wikipedia.org/wiki/Proton protons] and electrically neutral [http://en.wikipedia.org/wiki/Neutron neutrons] (except in the case of [http://en.wikipedia.org/wiki/Hydrogen-1 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 [http://en.wikipedia.org/wiki/Ion 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 [http://en.wikipedia.org/wiki/Isotope isotope] of the element.

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 [https://en.wikipedia.org/wiki/Proton protons] and electrically neutral [https://en.wikipedia.org/wiki/Neutron neutrons] (except in the case of [https://en.wikipedia.org/wiki/Hydrogen-1 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 [https://en.wikipedia.org/wiki/Ion 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 [https://en.wikipedia.org/wiki/Isotope 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 [http://en.wikipedia.org/wiki/Nanometer nanometer] and tiny masses [[proportional]] to the volume implied by these [[dimensions]]. Atoms can only be observed individually using special instruments such as the [http://en.wikipedia.org/wiki/Scanning_tunneling_microscope 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 [http://en.wikipedia.org/wiki/Radioactive_decay 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 [http://en.wikipedia.org/wiki/Atomic_orbital orbitals], and can undergo [[transitions]] between them by absorbing or emitting [http://en.wikipedia.org/wiki/Photon 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''.[http://en.wikipedia.org/wiki/Atom]

Chemical atoms, which in science now carry the simple name of "atom," are minuscule objects with [[diameters]] of a few tenths of a [https://en.wikipedia.org/wiki/Nanometer nanometer] and tiny masses [[proportional]] to the volume implied by these [[dimensions]]. Atoms can only be observed individually using special instruments such as the [https://en.wikipedia.org/wiki/Scanning_tunneling_microscope 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 [https://en.wikipedia.org/wiki/Radioactive_decay 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 [https://en.wikipedia.org/wiki/Atomic_orbital orbitals], and can undergo [[transitions]] between them by absorbing or emitting [https://en.wikipedia.org/wiki/Photon 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''.[https://en.wikipedia.org/wiki/Atom]

[[Category: Physics]]

[[Category: Physics]]