Changes

In [[chemistry]] and [[physics]], an '''atom''' ([[Greek language|Greek]] ''ἄτομος'' or ''átomos'' meaning "indivisible") is the smallest particle still characterizing a [[chemical element]]."Atom" in IUPAC Compendium of Chemical Terminology, Electronic version, http://goldbook.iupac.org/A00493.html. Accessed March 2007.</ref>

In [[chemistry]] and [[physics]], an '''atom''' ([[Greek language|Greek]] ''ἄτομος'' or ''átomos'' meaning "indivisible") is the smallest particle still characterizing a [[chemical element]]."Atom" in IUPAC Compendium of Chemical Terminology, Electronic version, [http://goldbook.iupac.org/A00493.html]. Accessed March 2007.

An atom consists of a dense [[atomic nucleus]] of positively-charged [[proton]]s and electrically-neutral [[neutrons]], surrounded by a much larger [[electron cloud]] consisting of negatively-charged [[electron]]. An atom is electrically neutral if it has the same number of protons as electrons. The number of protons in an atom defines the [[chemical element]] to which it belongs, while the number of neutrons determines the [[isotope]] of the element.

An atom consists of a dense [[atomic nucleus]] of positively-charged [[proton]]s and electrically-neutral [[neutrons]], surrounded by a much larger [[electron cloud]] consisting of negatively-charged [[electron]]. An atom is electrically neutral if it has the same number of protons as electrons. The number of protons in an atom defines the [[chemical element]] to which it belongs, while the number of neutrons determines the [[isotope]] of the element.