constant chemistry physics constant named scientist number constituent particles usually molecules contained substance given mole factor relates mass compound mass sample constant designated symbol value international system units previous definitions chemical quantity involved number historical term closely related constant defined differently number initially defined number atomic hydrogen meaning hydrogen number known constant german literature constant later number grams later relate amounts substance molecular weight instance hydrogen element having atomic mass number hydrogen similarly grams mass number atomic number number carbon number quantity numerical value constant given base units contrast constant dimension substance revisions base set units necessitated concepts chemical quantity number definition favor constant definition changes units proposed fix value constant exactly expressed unit end number means final agreed history constant named early 19th century italian scientist proposed volume gas given pressure temperature proportional number molecules regardless nature gas french physicist proposed naming constant honor won nobel prize physics largely work determining constant different methods value constant indicated estimated average diameter molecules air method equivalent calculating number particles given volume gas value number density formula particles ideal gas called constant honor related constant formula pressure gas constant absolute temperature connection root symbol constant german language literature refer distinguished units measurement accurate number require measurement single quantity atomic scales unit measurement possible time american physicist measured charge electron electric charge mole constant called constant known published works dividing charge mole charge single electron value number obtained newer calculations accurately determined values constant elementary charge originally proposed number refer number molecules oxygen exactly oxygen according definitions period term widely especially introductory works change constant came introduction mole base unit recognized substance independent dimension measurement recognition constant longer pure number unit measurement mole rare use units substance mole constant expressed units pound mole mole general role science constant scaling factor microscopic atomic scale observations nature provides relation physical properties example based values establishes following relationship gas constant constant formula constant elementary charge formula constant enters definition unified atomic mass unit formula mass constant measurement earliest accurate method measure value constant based principle measure constant electric charge carried mole divide elementary charge obtain constant formula classic experiment davis relies silver metal away cell passing constant electric current known time mass silver lost atomic weight silver constant given formula scientists devised method compensate silver lost mechanical causes conducted analysis silver determine atomic weight value conventional constant corresponds value constant values relative standard uncertainty electron mass measurement publishes values physical international use determines constant ratio mass electron rest mass electron formula relative atomic mass electron directly measured quantity mass constant defined constant electron rest mass calculated measured formula observed table main limiting factor precision constant uncertainty value constant contribute calculation known precisely ray crystal density methods modern method determine constant use ray single crystals produced today commercial facilities extremely high purity defects method defines constant ratio volume atomic volume formula formula number unit cell volume unit cell cubic packing arrangement unit cell volume measured determining single unit cell length sides cube practice measurements carried distance known distance planes denoted miller equal value relative uncertainty corresponding unit cell volume proportional composition sample measured taken account occurs stable natural variation proportions greater measurements atomic weight sample crystal calculated relative atomic masses known great accuracy measured density sample allows volume determined formula mass constant value volume relative standard uncertainty recommended values relative uncertainty constant ray crystal density method half times higher electron mass method international coordination simply called project collaboration begun early 1990s national measure constant ray crystal density method relative uncertainty project efforts kilogram terms universal physical constant measurements constant current definitions measurement constant indirect measurement constant formula measurements use highly polished spheres mass kilogram spheres measurement size density minimize effect coating inevitably forms surface measurements spheres natural composition relative uncertainty results inconsistent values constant derived balance measurements source believed known main uncertainty early measurements measurement composition atomic weight single crystal enriched grown kilogram spheres cut diameter measurements spheres uncertainty mass results expected late paper published january summarized result presented measurement constant
Avogadro constant