Atoms Mass Spec ppt

8/19/2019 Atoms Mass Spec ppt

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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&amples

'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!&%


$xample: +sotopes of carbon


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$%OTO!&%


$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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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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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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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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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&ample$ 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

Atoms Mass Spec ppt

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