CHARACTERISTICS OF ATOMSDOE-HDBK-1015/1-93Fundamentals of ChemistryCH-01Rev. 0Page 2Figure 1 Schematic of a Simple Atom (Helium)TheAtomStructureAll matter is composed of atoms, existing individually or in combination with each other. Anatom is an extremely small electrically-neutral particle. It is the smallest unit involved in thechemical change of matter. Atoms can be treated as distinct particles because they behave assuch chemically, but atoms themselves are composed of even smaller subparts. Understandingthese atomic subparticles is important in understanding chemistry.An atom is composed of a positively-charged nucleus orbited by one or more negatively-chargedparticles called electrons. A simplified schematic representation of this arrangement is illustratedin Figure 1. The nucleus is the core of an atom. It has a positive charge because it usuallyconsists of two particles, the neutron and the proton (hydrogen is the exception with only aproton in the nucleus). The neutrons are electrically neutral, and the protons are electricallypositive. A nucleus with one proton has a charge of +1 (or simply 1), and a nucleus with twoprotons has a +2 charge. Together the neutrons and protons give the nucleus its mass, but theproton alone gives the nucleus its positive charge.Neutrons and protons are relatively massive and are essentially equal in mass.
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business