chapter 2b the atomic structure
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The Atomic StructureThe Atomic Structure
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Structure of an atomStructure of an atom
ShellShell
NucleusNucleus( proton & neutron )( proton & neutron )
ElectronElectron
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The historical development ofThe historical development of
atomic modelsatomic modelsAtomic ModelAtomic Model CharacteristicsCharacteristics
John DaltonJohn Dalton Atom was imagined as aAtom was imagined as a
small indivisible ballsmall indivisible ball
J.J.ThomsonJ.J.Thomson DiscoveredDiscovered electronelectron
Ernest RutherfordErnest Rutherford DiscoveredDiscoveredprotonproton inin
nucleusnucleus
Neils BohrNeils Bohr Electrons move inElectrons move in shellsshells
around the nucleusaround the nucleus
James ChadwickJames Chadwick DiscoveredDiscovered neutronsneutrons inin
nucleusnucleus
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Structure of an atomStructure of an atom
ShellShell
NucleusNucleus( proton & neutron )( proton & neutron )
ElectronElectron
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SubatomicSubatomic
particlesparticles
SymbolSymbol RelativeRelative
massmass
RelativeRelative
electricelectric
chargecharge
ProtonProton pp 11 +1+1
NeutronNeutron nn 11 00
ElectronElectron ee 00 --11
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As the masses of protons & neutronsAs the masses of protons & neutrons
are much greater than electrons, mostare much greater than electrons, most
of theof the masses of an atom concentratedmasses of an atom concentrated
in the nucleus.in the nucleus.NucleusNucleus has an overallhas an overallpositive chargepositive charge..
An atom consists of an equal number ofAn atom consists of an equal number of
electrons & protons. Thus, an atom iselectrons & protons. Thus, an atom is
electrically neutral.electrically neutral.
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Proton NumberProton Number
Is the number ofIs the number ofprotonsprotons in an atom.in an atom.
Since atoms areSince atoms are neutralneutral, the proton, the proton
number is also the number ofnumber is also the number of
electronselectrons in the atom.in the atom.
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Nucleon NumberNucleon Number
Is the total number ofIs the total number ofprotons &protons &
neutronsneutrons in an atom.in an atom.
Nucleon numberNucleon number
= protons + neutrons= protons + neutrons
Is also known asIs also known as mass number.mass number.
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Symbol of an elementSymbol of an element
Nucleon numberNucleon number 2323
Proton numberProton number 1111NaNa
Number of protons, electrons & neutrons ?Number of protons, electrons & neutrons ?
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IsotopesIsotopes
Atoms of theAtoms of the same elementsame element with thewith the
same number of protonssame number of protonsbutbut differentdifferent
numbers of neutrons.numbers of neutrons.
Or, atoms with theOr, atoms with the same proton numbersame proton number
butbut different nucleon number.different nucleon number.
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ElementElement IsotopesIsotopes ProtonsProtons ElectronsElectrons NeutronsNeutrons
HydrogenHydrogen
HydrogenHydrogen--11
HydrogenHydrogen--22
HydrogenHydrogen--33
11
11
11
11
11
11
00
11
22
OxygenOxygen
OxygenOxygen--1616
OxygenOxygen--1717
OxygenOxygen--1818
88
88
88
88
88
88
88
99
1010
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Isotopes of an element have theIsotopes of an element have the samesame
chemical propertieschemical propertiesbutbut differentdifferent
physical properties.physical properties.
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Uses of isotopesUses of isotopes
IsotopesIsotopes PurposesPurposes
CobaltCobalt--6060 Treatment of cancerTreatment of cancer
SodiumSodium--2424 Trace leaks in gas/water pipesTrace leaks in gas/water pipes
IodineIodine--131131 Treatment of thyroid diseasesTreatment of thyroid diseases
CarbonCarbon--1414 Estimate age of fossilsEstimate age of fossilsKryptonKrypton--8585 Control thickness of plasticControl thickness of plastic
sheetssheets
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The Electronic Structure of an AtomThe Electronic Structure of an Atom
The first
shell (2e)
The second
shell (8e)
The thirdshell (8e)
Nucleus
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Electron ArrangementElectron Arrangement
For a neutral atom,For a neutral atom,
number of electrons = number of protons.number of electrons = number of protons.
Electrons occupy the shellElectrons occupy the shell closest to theclosest to thenucleusnucleus first. Electron only start occupyfirst. Electron only start occupy
the next shell when the previous shell hasthe next shell when the previous shell has
been fully occupied.been fully occupied.
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H : 1H : 1
He : 2He : 2
Carbon : 2.4Carbon : 2.4
Na : 2.8.1Na : 2.8.1
Ca : 2.8.8.2Ca : 2.8.8.2
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Valence electronsValence electrons
Valence electrons are electrons foundValence electrons are electrons found
in thein the outermost occupied shelloutermost occupied shell ( the( the
furthest from the nucleus ) of anfurthest from the nucleus ) of anatom.atom.
The number of valence electrons inThe number of valence electrons inan atom can be determined from itsan atom can be determined from its
electron arrangementelectron arrangement..
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