Post on 07-Jul-2018
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Atomic Structure
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Part 1
The Atom
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All atoms, with the exception of H, are made up of 3subatomic particles: protons, neutrons and electrons.
Hydrogen is the simplest atom (1 proton & 1 electron
Atomic radius is on the order of 1!"1! m. Atoms are mostly empty space. #rotons and neutrons are located in the nucleus. $lectrons are found in energy le%els (shells surrounding
the nucleus.
ATOM BASICS
General Concepts
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Cultural bias in scientific history?
Atom' )ree* word meaningindi%isible'
+n -! /$, the )ree* philosopher,0emocritus, suggested that the
uni%erse was made of indi%isible units
or so we2%e heard. Δημόκριτος, Dēmokritos,"chosen of the people“
(46 ! # $C%&
“'othn) e*sts +t ato-s an. e-pt/space0 e1er/thn) else s opnon23
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Cultural bias in scientific history?
$ddie +ard(0ress to 4ill
“ )re5 p n %rope,
5here the hstor/ co-es fro-23
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Cultural bias in scientific history? 5any historians belie%e the idea
was first proposed at least acentury earlier in the +ndian
subcontinent.
6he theory of atomism was alsomuch de%eloped in both /hineseand Arabic culture during the 0ar*Ages in $urope, when theteachings of the church dictatedmuch of 7estern thought.
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JOHN DALTON
0alton2s Atomic 6heory (proposed in 18!8: All elements are made of tiny atoms. Atoms cannot be subdi%ided. Atoms of the same element are exactly ali*e. Atoms of different elements can 9oin to form
molecules.
E id f S b i
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Thompson and Millikan are gi%en credit for
the first disco%eries relating to electrons.
Robert Millikan J.J. Thompson
Evidence for SubatomicParticles
.. 6homson(18;< " 1=!
1=!< >obel
E id f S b i
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Rutherfor disco%ered the positi%elycharged nucleus.
Evidence for SubatomicParticles
Ernest Rutherford
?bser%ations:
1 5ost of the particles passeddirectly through " nodeflection
- @ome of the particles weredeflected somewhat fromtheir path.
3 @ome of the particlesbounced bac* in the samedirection from which they
approached the gold foil.
$rnest utherford(18B1 " 1=3B
1=!8 >obel
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Relative mass and charge of
subatomic particles
ctal -ass of a proton7 826#9 * 894 )
netron -ass s 1rtall/ .entcal
electron s 8:9 of ths -ass
ctal char)e of an electron7 8269 * 8;8
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!erioic "ey
<
C/arbon
1-.!11
Atomic number (#
$lement2s symbol
$lement2s name
Atomic mass (A
C of protons D E
C of electrons D C of protons (in a neutral atom
C of neutrons D A"E
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horthand notation for an
atom or ion
? @n=:n;
MA #$
A protons = A netrons
AT%MIC #$
A protons
(5hch s B A electrons
f a netral ato-&
C!AR"E7
lea1e +lan f nB(netral ato-&
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E&les
'mbol Atomic
number
()*
Mass
number
(A*
# protons # neutrons # electrons
4 < 4 > 4
9 4 9 9 8D8# # 8# 9 8D
e=,
+-,!
-!/a−/l3B1B
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$%OTO!&%
+sotopes: atoms that ha%e the same C of protons,but a different C of neutrons.
$xample: +sotopes of hydrogen
1pF, 1e", !n
1pF, 1e", 1n
1pF, 1e", -n
H11
H-
1
H31
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$%OTO!&%
+sotopes: atoms that ha%e the same C of protons,but a different C of neutrons.
$xample: +sotopes of carbon
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$%OTO!&%
+sotopes: atoms that ha%e the same C of protons,but a different C of neutrons.
$xample: +sotopes of chlorine
1BpF, 1Be", 18n
1BpF, 1Be", -!n
/l3;1B
/l3B1B
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RELATIVE AT%MIC MA$5e)hte. -ean -olar -ass of ato-s of ele-ents2
%*a-ple7 Ehe t5o sotopes of chlorne occr n the rato of
782 Ehs, natrall/ occrrn) chlorne contans #>F an.
9>F 2 eter-ne the relat1e ato-c -ass of chlorne2
1!!
3B-;(3;B;( ×+×gGmol;.3;=
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Part +
Mass Spectrometry
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The Mass pectrometer
Helat1e ato-c -asses (a-on) other
thn)s 5e 5ll .scss 5hen 5e )et to
or)anc che-str/& can +e .eter-ne.
sn) ths nstr-ent2
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!o, it ,or-s (. basic steps*$
vapori/ation$ f the sa-ple s not alrea./ as
)as, the sa-ple s heate. to ths pont210
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!o, it ,or-s (. basic steps*$
ioni/ation$ sa-ple s +o-+ar.e. 5th a strea- of
h)h ener)/ electons2 n practce, the nstr-ent
s set so that onl/ ons 5th a sn)le post1e
char)e are for-e. (I=&2
+0
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!o, it ,or-s (. basic steps*$
acceleration$ resltn) npost1e ons pass
thro)h slts n parallel plates n.er the nflence
of an electrc fel.2
0
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!o, it ,or-s (. basic steps*$
deflection$ ons are then passe. o1er an e*ternal
-a)netc fel.2 Ehe -a)netc fel. cases the ons to+e .eflecte., an. the a-ont of .eflectons s
proportonal to the char)e:-ass rato2 ons 5th
smaller -asses are .eflecte. more than hea1er
ons2 ons 5th h)her char)es are .eflecte. -ore as
the/ nteract -ore effect1el/ 5th the -a)netc fel.2
20
Jea1er
partcles
l)hter
partcles
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!o, it ,or-s (. basic steps*$
detection$ post1e ons of a partclar
-ass:char)e rato are .etecte. an. a s)nal s
sent to a recor.er2 Ehe stren)th of the s)nal s a
-easre of the n-+er of ons 5th thatchar)e:-ass rato that are .etecte.2
.0
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E&le$ Kn. the relat1e ato-c -ass (r & of
natrall/ occrrn) lea. fro- the .ata +elo52 Hecor.
/or ans5er to the nearest tenth2
Isotopicmass
Relativeabundance
3 relativeabundance
94 29 9
96 924 9249# 929 929
9D >29 >9
203 204 205 206 207 208 209
0
1
2
3
4
5
6
0.2
2.42.2
5.2
Mass Spectrum of Pb
mass/charge
relative abundance
4igure$ Ehe Iass Lpectr- of 'atrall/ Mccrrn) Nea.
9#29
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Radioisotopes
Nucleus staility !epe"!supo" the ala"ce et#ee"the "umer o$ proto"s a"!"eutro"s.
Nuclei that co"tai" too
ma"y or too $e# "eutro"sare u"stale %ra!ioacti&e'a"! cha"(e to $orm morestale "uclei y (i&i"( o)
ra!iatio".
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Radioisotopes
Alpha ( ): particles %i!e"tical to helium"uclei' emitte! y "uclei #ith too ma"yproto"s.
Beta ( ): electro"s are e*ecte! %o#i"( to"eutro" !ecay' $rom "uclei #ith too ma"y"eutro"s.
amma (γ): rays that are a hi(h+e"er(y$orm o$ electroma("etic ratio".
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!ses of radioisotopes
ca" e use! to (e"erate e"er(y i""uclear po#er pla"ts %,ssio"'-sterilie sur(ical i"strume"ts i"
hospitals- preser&e $oo!- !etectcrac/s i" structural materials- etc.
hile the hi(h e"er(y "ature o$ra!ioacti&ity ca" e use! sa&e huma"li$e- u"co"trolle! le&els o$ eposureca" ha&e uite the opposite e)ect.
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"arbon#$% dating
ecays as %eta emissio"' at a/"o#" rate.
al$ li$e %time it ta/es$or 50 o$ sample to!ecay' $or +14 is 5730years.
>e/ 1,B!1"
1,< +→
−
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"arbon#$% dating
+14 co"ti"ually $orms i"the upper atmospherea"! is i" euilirium #ith
+12 %co"ce"tratio"s areco"sta"t'.
As li&i"( thi"(s $u"ctio"-they co"sta"tly recyclecaro"- thus mai"tai"i"(a co"sta"t +14+12ratio.
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"arbon#$% dating
As li&i"( thi"(s $u"ctio"- they co"sta"tlyrecycle caro"- thus mai"tai"i"( a co"sta"t+14+12 ratio.
The +14+12 ratio $alls y 50 e&ery 5730years a$ter the !eath o$ a li&i"( or(a"ism.
Ieasre-ent of crrent act1t/
allo5s s to .eter-ne ho5 lon)a)o a fossl 5as .eposte.2 fter
>, /ears, the act1t/ s so lo5
that other ra.oncl.es -st +e
se. for accrate fossl .atn)2
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"obalt#&' used inradiotherap
a!iotherapy %ra!iatio" therapy'tar(ets io"ii"( ra!iatio" atca"cer cells- !ama(i"( the(e"etic material o$ these cells y/"o#c/i"( o) electro"s a"!ma/i"( it impossile $or thesecells to (ro# a"! !i&i!e. Co;6 s co--onl/ se. as t e-ts 1er/ penetratn)
)a--a ra.aton 5hen ts protons an netrons chan)e
ther relat1e postons n the ncles2
ltho)h ra.otherap/ .a-a)es +oth cancer an. nor-al
cells, the nor-al cells are a+le to reco1er f the treat-ent
s carefll/ controlle.2
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odine#$*$ as a medicaltracer
mitter o$ oth eta a"! (ammara!iatio".
Ha.osotopes ha1e sa-e che-cal propertes as an/
other ato- of the sa-e ele-ent an. so the/ pla/ the
sa-e roll n the +o./0 ho5e1er, ther postons, nle other
sotopes, can +e -ontore. +/ .etectn) ra.aton le1els,
-an) the- sta+le as -e.cal tracers2
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odine#$*$ as a medicaltracer
:+131 i" the $orm o$ so!iumio!i!e ca" e use! toi"&esti(ate acti&ity o$ the
thyroi! (la"! a"! to!ia("ose a"! treat thyroi!ca"cer.
Jalf lfe for ;88 s short, D .a/s, so t s Ocl/ el-nate.
fro- the +o./2
nother sotope, ;89> s se. n treat-ent of prostate
cancer (half;lfeBD .a/s&2