Diatom bi di baezik patikul of dikemikal elements. An atom konsis of anukleus ofprotons and jeneralyneutrons, wey dey soraunded by an elektromagnetikaly-baund swarm ofelektrons. Di kemikal elements dey diferenshiated from each oda bai di nomba of protons wey dey dia atoms. For exampul, eni atom wey kontain 11 protons bisodium, and eni atom wey kontain 29 protons bikoppa. Atoms wey get di sem nomba of protons but a diferen nomba of neutrons biisotopes of di sem element.
Atoms dey veri smol, typikally araund 100 pikometas akros. A human hair bi abaut a million kabon atoms waid. Dis dey smola than di shortes waivlength of visibul lait, which mean say humans no fit si atoms with konvenshonal maikroskops. Atoms dey so smol sotey to akuraetli predit their behavio bai yuzinklassikal fysiks no dey posibul due toquantum effekts.
Moh than 99.94% of an atommass dey di nukleus. Protons get a positivelektrik charj and neutrons no get charj, so di nukleus dey positivli charjd. Di elektrons dey negativli charjd, and dis oposin charj bi wetin dey baind dem to di nukleus. If di nombas ofprotons and elektrons dey equal, as dem normally dey, then di atom dey elektrikali neutral as a whol. If an atom get moh elektrons than protons, then e get an ovaraul negativ charj, and so bi a negativion (or anion). Konvasli, if get moh protons than elektrons, e get a positiv charj, and so bi a positiv ion (or kation).
For 1897,J. J. Thomson diskova saykathod rays no bi elektromagnetik waivs but konsis of patikuls bikos Dem fit dey deflekted bai elektrik and magnetik fields. Him measure diz patikuls to dey 1,800 taims laita thanhydrojin (di laites atom). Thomson konklud say diz patikuls kom from di atoms wey dey di kathod—dem bisubatomik patikuls. Him kol diz niu patikulskopuskuls butelektrons bi wetin wi kom to sabi dem as. Thomson also show say elektrons dey identikal to di patikuls wey dey komot fromphotoelektrik and radioaktiv materials.[1] Wi quickli rekognaiz say elektrons bi di patikuls wey karielektrik korrents for metal waiya-dem.[2] Thomson konklud say diz elektrons join togeda from di veri atoms of di kathod for him instruments, wey mean say atoms no dey indivisibul as Dalton been tink.
DiGeija–Marsden experiment: Left: results wey wi expekt: alfa patikuls wey dey pas thru di plum pudin model of di atom with neglijibul deflekshon. Raight: Wetin wi obsav: koncentrated positiv charj of di nukleus deflekt a smol poshon of di patikuls.
J. J. Thomson been tink say di negativli-charjd elektrons dey distributed thruaut di atom for a sea of positiv charj wey dey distributed akros di whol volum of di atom.[3] Dis model bi wetin wi sometaims sabi as diplum pudin model.
Ernest Ruthaford and him koleaguesHans Geija andErnest Marsden kom to daut di Thomson model afta dem encaunta difikultis wen dem trai to build instrument to measure di charj-to-mass ratio ofalfa patikuls (diz bi positivli-charjd partikuls wey cetain radioactiv substansis such asradium dey emit). Di alfa patikuls dey skatad bai di air for di detekshon chamba, wey mek di measurements dey unreliabul. Thomson been enkaunta a simila problem for him work on kathod rays, wey him solv bai kreatin a nia-pafekt vakuum for him instruments. Ruthaford no tink say him ga run into dis sem problem bikos alfa patikuls dey much hevi than elektrons. Akordin to Thomson's model of di atom, di positiv charj for di atom no dey koncentrated enouf to prodius elektrik field wey ga dey strong enouf to deflekt an alfa patikul, and di elektrons dey so laitweight so dat dem ga dey push aside efotlesli bai di much hevi alfa partikuls. Yet skatarin dey, so Ruthaford and him kolleagues decide to investigaet dis skatarin kiafuli.[4]
For 1938, di Jerman kemistOtto Hahn, a student of Ruthaford, direkt neutrons onto uranium atoms expektin say natransuranium elements ga bi di results. Insted, him kemikal experiments showbarium as di produkt. A year afta,Lise Meitna and ha nefewOtto Frisch verifai say Hahn's result bi di fes experimentalnukle fission. For 1944, Hahn receiv diNobel Prize for Kemistri. Despite Hahn's efots, di kontribushons of Meitna and Frisch no dey rekognaizd.
For di 1950s, di development of impruvdpatikul accelerators andpatikul detetors kom allow saientists to stodi di impakts of atoms wey dey muv for hai enejis. Dem diskova say Neutrons and protons bihadrons, or komposits of smola patikuls wey dem kolquarks.
Though di wodatom been orijinali mean patikul wey no fit dey cut into smola patikuls, for moden saientifik yuz di atom konsis of varioussubatomik patikuls. Di konstituent patikuls of a atom bi dielektron, diproton and dineutron.
Dibaindin eneji wey dey needed for a nukleon to eskayp di nukleus, for various isotops
Aul di baund protons and neutrons for an atom mek up a tainiatomik nukleus, and dey kolektivli kolnukleons. Di radius of a nukleus dey approximaetli equal tofemtometas, whe bi di total nomba of nukleons.[5] Dis dey much smola than di radius of du atom, wey dey 105 fm.
Atoms of di semelement get di sem nomba of protons, wey bi diatomik nomba. Within a singul element, di nomba of neutrons fit vari, to detamyn diisotop of dat element. Di total nomba of protons and neutrons detamyn dinuklyde. Di nomba of neutrons relativ to di protons dey detamyn di stabiliti of di nukleus, with certain isotops sufarinradioactiv dikay.
Bai definishon, eni tuw atoms with an identikal nomba ofprotons for dia nuklei bilong to di semkemikal element. Atoms with equal nomba of protons but a diferen nomba ofneutrons dey diferen isotops of di sem element. For exampul, aul hydrojin atoms dey admit exaktli a proton, but isotops exist with no neutrons (hydrojin-1, bai fa di mos komon fom, wey bi also protium), a neutron (deuterium), tuw neutrons (tritium) andmoh than tuw neutrons. Di elements wey wi sabi fom a set of atomik nomba, from di singul-proton elementhydrojin up to di 118-proton elementoganesson.
Di laj majoriti of an atom's mass dey kom from di protons and neutrons wey mek up am. Di total nomba of diz patikuls (wey bi "nukleons") for a given atom bi dimass number. E bi a positiv intija and daimenshonles (instead of havin dimenshon of mass), bikos e dey expres a kaunt. An exampul of yuz of a mass nomba bi "kabon-12," wey get 12 nukleons (six protons and six neutrons).
Atoms dey lak a wel-defined auta baundari, so dia daimenshon yuzuali dey deskraibd in tems of anatomik radius. Dis bi a measure of di distans aut to which di elektron klaud dey extend from di nukleus.[6]
