ATOMICTHEORY
LearningOutcomes
Bytheendofthisunitthelearnerwillbeableto:
a) Describetheatomicstructure
b) Explaintheperiodictableofelements
ATOM
Anatomisthesmallestunitofmatterthatretainsallofthechemicalpropertiesofanelement.Atomscombi
netoformmolecules,whichtheninteracttoformsolids,gases,orliquids.Forexample,wateriscomposed
ofhydrogenandoxygenatomsthathavecombinedtoformwatermolecules.
AtomicParticles
Atomsconsistofthreebasicparticles:protons,electrons,andneutrons.Thenucleus(center)oftheatomco
ntainstheprotons(positivelycharged)andtheneutrons(nocharge).Theoutermostregionsoftheatomare
calledelectronshellsandcontaintheelectrons(negativelycharged).Atomshavedifferentpropertiesbas
edonthearrangementandnumberoftheirbasicparticles.
Theoppositechargecausestheatomtohaveaforceofattractionwhichkeepstheelectronstorevolvearoun
dtheshell.
Differentelementshavedifferentnumberofshellswiththehighestbeingsevenshells.
TheshellsarenumberedfromK-Q
Kshellholdsamaximumoftwoelectrons,Lmaximumof8,Mmaximum18,Nmaximumof32,noshellhol
dsmorethan32electrons.
Anatomwithequalnumberofelectronsandprotonsissaidtobeelectricallyneutral.
Atomwithsameouterorbitalelectronshavesimilarchemicalproperties.
Outerorbitalelectronsarereferredasvalenceelectronsandplaysmajorpartinchemicalcombinations.
AtomicMass
Protonsandneutronshaveapproximatelythesamemass,about1.67×10-
24grams.Scientistsdefinethisamountofmassasoneatomicmassunit(amu)oroneDalton.Althoughsimi
larinmass,protonsarepositivelycharged,whileneutronshavenocharge.Therefore,thenumberofneutro
nsinanatomcontributessignificantlytoitsmass,butnottoitscharge.
Electronsaremuchsmallerinmassthanprotons,weighingonly9.11×10-
28grams,orabout1/1800ofanatomicmassunit.Therefore,theydonotcontributemuchtoanelement’sov
LearningOutcomes
Bytheendofthisunitthelearnerwillbeableto:
a) Describetheatomicstructure
b) Explaintheperiodictableofelements
ATOM
Anatomisthesmallestunitofmatterthatretainsallofthechemicalpropertiesofanelement.Atomscombi
netoformmolecules,whichtheninteracttoformsolids,gases,orliquids.Forexample,wateriscomposed
ofhydrogenandoxygenatomsthathavecombinedtoformwatermolecules.
AtomicParticles
Atomsconsistofthreebasicparticles:protons,electrons,andneutrons.Thenucleus(center)oftheatomco
ntainstheprotons(positivelycharged)andtheneutrons(nocharge).Theoutermostregionsoftheatomare
calledelectronshellsandcontaintheelectrons(negativelycharged).Atomshavedifferentpropertiesbas
edonthearrangementandnumberoftheirbasicparticles.
Theoppositechargecausestheatomtohaveaforceofattractionwhichkeepstheelectronstorevolvearoun
dtheshell.
Differentelementshavedifferentnumberofshellswiththehighestbeingsevenshells.
TheshellsarenumberedfromK-Q
Kshellholdsamaximumoftwoelectrons,Lmaximumof8,Mmaximum18,Nmaximumof32,noshellhol
dsmorethan32electrons.
Anatomwithequalnumberofelectronsandprotonsissaidtobeelectricallyneutral.
Atomwithsameouterorbitalelectronshavesimilarchemicalproperties.
Outerorbitalelectronsarereferredasvalenceelectronsandplaysmajorpartinchemicalcombinations.
AtomicMass
Protonsandneutronshaveapproximatelythesamemass,about1.67×10-
24grams.Scientistsdefinethisamountofmassasoneatomicmassunit(amu)oroneDalton.Althoughsimi
larinmass,protonsarepositivelycharged,whileneutronshavenocharge.Therefore,thenumberofneutro
nsinanatomcontributessignificantlytoitsmass,butnottoitscharge.
Electronsaremuchsmallerinmassthanprotons,weighingonly9.11×10-
28grams,orabout1/1800ofanatomicmassunit.Therefore,theydonotcontributemuchtoanelement’sov
