chapter 2b the atomic structure

8/8/2019 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



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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chapter 2b the atomic structure

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