37968874 chapter 2b the atomic structure

8/3/2019 37968874 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 of atomicThe historical development of atomic

modelsmodelsAtomic Model Characteristics

John Dalton Atom was imagined as asmall indivisible ball

J.J.Thomson Discovered electron

Ernest Rutherford Discoveredproton in nucleus

Neils Bohr Electrons move in shellsaround the nucleus

James Chadwick Discovered neutrons in

nucleus


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Structure of an atomStructure of an atom

ShellShell

NucleusNucleus( proton & neutron )( proton & neutron )

ElectronElectron


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As the masses of protons & neutrons areAs the masses of protons & neutrons are

much greater than electrons, most of themuch greater than electrons, most of the

masses of an atom concentrated in themasses of an atom concentrated in the

nucleus.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 ofelectronselectrons 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 protons butbut 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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Element Isotopes Protons Electrons Neutrons

Hydrogen

Hydrogen-1

Hydrogen-2Hydrogen-3

1

11

1

11

0

12

Oxygen

Oxygen-16

Oxygen-17Oxygen-18

8

88

8

88

8

910


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Isotopes of an element have theIsotopes of an element have the samesame

chemical propertieschemical properties butbut differentdifferent

physical properties.physical properties.


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Uses of isotopesUses of isotopes

Isotopes Purposes

Cobalt-60 Treatment of cancer

Sodium-24 Trace leaks in gas/water pipesIodine-131 Treatment of thyroid diseases

Carbon-14 Estimate age of fossilsKrypton-85 Control thickness of plastic

sheets


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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 occupy thefirst. Electron only start occupy the

next shell when the previous shell has beennext shell when the previous shell has been

fully occupied.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 an atom.furthest from the nucleus ) of an atom. The number of valence electrons in anThe number of valence electrons in an

atom can be determined from itsatom can be determined from its

electron arrangementelectron arrangement..


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H : 1 VE : 1H : 1 VE : 1

He : 2He : 2 VE : 2VE : 2

Carbon : 2.4Carbon : 2.4 VE : 4VE : 4

Na : 2.8.1Na : 2.8.1 VE : 1VE : 1 Ca : 2.8.8.2Ca : 2.8.8.2 VE : 2VE : 2


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Element Symbol Protonnumber

Nucleonnumber

Numberof proton

Numberof

electron

Numberof

neutron

Electronarrange-ment

Numberof valenceelentron

37968874 chapter 2b the atomic structure

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