ch25 lesson25_2

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25.2 Nuclear Transformations >25.2 Nuclear Transformations >

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Chapter 25uclear Che!istry

25.1 uclear Radiation

25.2 Nuclear Transformations

25." #ission and #usion

25.$ Radiation in %our &ife

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What is the source of radon in homes?

CHEMISTR!"#

Radon !ay

accu!ulate in a'ase!ent that is

not (ell ventilated.

)est *its are

availa'le to

!easure the

levels of radon in a 'uilding.

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uclear +ta'ility anduclear +ta'ility and

ecayecay

Nuclear Sta$ilit% and &eca%

-hat deter!ines the type of decay a

radioisotope undergoes

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ecayecay

)he nuclear forceis an attractive force

that acts 'et(een allnuclear particles that

are e/tre!ely close together, such as

protons and neutrons in a nucleus.

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ecayecay

)he nuclear forceis an attractive force

that acts 'et(een allnuclear particles that

are e/tre!ely close together, such as

protons and neutrons in a nucleus.

0 At these short distances, the nuclear force

do!inates over electro!agnetic repulsions

and holds the nucleus together.

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)he sta'ility of a nucleus depends on theratio of neutrons to protons.

Inter'retata

0 )his graph

sho(s thenu!'er of

neutrons vs. the

nu!'er of

protons for all

*no(n sta'le

nuclei.

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Inter'retata

0 )he region of the

graph in (hichthese points are

located is called

the $and of

sta$ilit%.

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Inter'retata

0 #or ele!ents of lo(

ato!ic nu!'er4'elo( a'out 26,

this ratio is a'out 1.

0 A'ove ato!ic

nu!'er 2, sta'lenuclei have !ore

neutrons than

protons.

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ecayecay

A nucleus !ay 'e unsta'le and undergo

spontaneous decay for different reasons.

)he neutron8to8proton ratio in aradioisotope deter!ines the type of decay

that occurs.

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ecayecay

+o!e nuclei are unsta'le 'ecause they

have too !any neutrons relative to thenu!'er of protons.

0 -hen one of these nuclei decays, a neutron

e!its a 'eta particle 4fast8!oving electron6 fro!the nucleus.

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ecayecay





9 A neutron that e!its an electron 'eco!es a proton.

n1

p :1

1 e

91

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ecayecay





9 A neutron that e!its an electron 'eco!es a proton.

n1

p :1

1 e

91

9 )his process is *no(n as 'eta e!ission.

9 It increases the nu!'er of protons (hile

decreasing the nu!'er of neutrons.

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ecayecay

Radioisotopes that undergo 'eta e!ission

include the follo(ing.

Cu

27 ;n :

" e

91

C1$

:1$

e

91

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ecayecay

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ecayecay

A 'ositronis a particle (ith the !ass of anelectron 'ut a positive charge.

0 Its sy!'ol is e.

0 uring positron e!ission, a proton changes toa neutron, =ust as in electron capture.

:1

>3

5 >e :3

$ e

:1

25.2 Nuclear Transformations >



ecayecay

uclei that have an ato!ic nu!'er greater

than 3" are radioactive.

0 )hese nuclei have 'oth too !any neutrons and

too !any protons to 'e sta'le.

9 )herefore, they undergo radioactive decay.

9 Alpha e!ission increases the neutron8to8proton

ratio, (hich tends to increase the sta'ility of the

nucleus.

0 ?ost of the! e!it alpha particles.

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ecayecay

In alpha e!ission, the !ass nu!'er

decreases 'y four and the ato!ic nu!'er

decreases 'y t(o.

Ra22

33 Rn : @e222

3

$

2

)h2"2

7 Ra : @e223

33

$

2

+

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ecayecay

Recall that conservation of !ass is an

i!portant property of che!ical reactions.

0 In contrast, !ass is not conserved duringnuclear reactions.

0 An e/tre!ely s!all uantity of !ass is

converted into energy released duringradioactive decay.

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&urin( nuclear deca%) if the atomicnum$er decreases $% one $ut the mass

num$er is unchan(ed) the radiation

emitted is

*. a positron.

+. an alpha particle.

C. a 'eta particle.

&. a proton.

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&urin( nuclear deca%) if the atomicnum$er decreases $% one $ut the mass

num$er is unchan(ed) the radiation

emitted is

*. a 'ositron.

+. an alpha particle.

C. a 'eta particle.

&. a proton.

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@alf8&ife@alf8&ife

Half,-ife

@o( !uch of a radioactive sa!ple

re!ains after each half8life

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1

2A half,life4t 6 is the ti!e reuired for one8half of the nuclei in a radioisotope sa!ple

to decay to products.

Inter'retBraphs

After each half8

life, half of the

original

radioactive

ato!s havedecayed into

ato!s of a ne(

ele!ent.

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@alf8&ife@alf8&ife

@alf8lives can 'e as short as a second or as

long as 'illions of years.

Half,-ies of Some Naturall% "ccurrin( Radioisoto'es

Isoto'e Half,life Radiation emitted

Car'on81$ 5." 1"years

Potassiu!8$ 1.25 17years ,

Radon8222 ".3 days

Radiu!822 1. 1"years ,

)horiu!82"$ 2$.1 days ,

Draniu!82"5 . 13years ,

Draniu!82"3 $.5 17years

Com'arin( Half,-ies

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@alf8&ife@alf8&ife

0 +cientists use half8lives of so!e long8ter!

radioisotopes to deter!ine the age of ancient

o'=ects.

0 ?any artificially produced radioisotopes have

short half8lives, (hich !a*es the! useful in

nuclear !edicine.

9 +hort8lived isotopes are not a long8ter!

radiation haard for patients.

Com'arin( Half,-ies

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@alf8&ife@alf8&ife

Com'arin( Half,-ies

0 )he age of uraniu!8

containing !inerals can 'eesti!ated 'y !easuring

the ratio of uraniu!82"3 to

lead82.

0 >ecause the half8life of

uraniu!82"3 is $.5 17

years, it is possi'le to use

its half8life to date roc*s as

old as the solar syste!.

Draniu!82"3 decays through a co!ple/ series of

unsta'le isotopes to the sta'le isotope lead82.

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#ranium com'ounds are found inroc/s and in soils that form from theseroc/s. Ho0 can these uranium

com'ounds lead to a $uildu' of radonin homes and other $uildin(s?

CHEMISTR!"#

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#ranium com'ounds are found inroc/s and in soils that form from theseroc/s. Ho0 can these uranium

com'ounds lead to a $uildu' of radonin homes and other $uildin(s?

CHEMISTR!"#

Radon gas is a product of the decay of

uraniu!. As the uraniu! co!pounds in

the soil 'eneath ho!es and 'uildings

decay, radon is produced and seeps into

the structure.

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@alf8&ife@alf8&ife

Radiocar$on &atin(Plants use car'on dio/ide to producecar'on co!pounds, such as glucose.

0 )he ratio of car'on81$ to other car'on isotopesis constant during an organis!Fs life.

0 -hen an organis! dies, it stops e/changing

car'on (ith the environ!ent and its radioactive C ato!s decay (ithout 'eing replaced.

0 Archaeologists can use this data to esti!ate

(hen an organis! died.

1$

2 2 N l T f i

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@alf8&ife@alf8&ife

E1'onential &eca% unction

0 Astands for the a!ount re!aining.

0 Astands for the initial a!ount.

0 nstands for the nu!'er of half8lives.

%ou can use the follo(ing euation to

calculate ho( !uch of an isotope (ill

re!ain after a given nu!'er of half8lives.

AG A1

2

n

25 2 N l T f ti

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@alf8&ife@alf8&ife

0 )he e/ponent nindicates ho( !any ti!es A

!ust 'e !ultiplied 'y to deter!ine A.1

2

AG A1

2

n


25 2 N l T f i25 2 N l T f ti f f

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@alf8&ife@alf8&ife

&eca% of Initial *mount 3A4 of

Radioisoto'e

Half,-ife *mount Remainin(

A 4 6G A

1 A 4 61G A

2 A 4 62G A

)his ta'le sho(s e/a!ples in (hich

nG 1 and nG 2.


12

12

12

12

12

12

25 2 N l T f ti25 2 N l T f ti

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#sin( Half,-ies in Calculations

Sam'lePro'le! 25.1

Car'on81$ e!its 'eta radiation and decays (ith a

half8life 4t 6 of 5" years. Assu!e that you start

(ith a !ass of 2. 1912g of car'on81$.

12

a. @o( long is three half8lives

$. @o( !any gra!s of the

isotope re!ain at the end ofthree half8lives

25 2 N l T f ti25 2 N l T f ti >

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6N"WNS #N6N"WNS

" half8lives G years

!ass re!aining G g

*nal%7e -ist the /no0ns and the un/no0ns.8

Sam'lePro'le! 25.1

0 )o calculate the length of three half8lives,

!ultiply the half8life 'y three.

0 )o find the !ass of the radioisotope

re!aining, !ultiply the original !ass 'y for

each half8life that has elapsed.

12

t G 5" years

initial !ass 4A6 G 2. 1912 g

nu!'er of half8lives 4n6G "

12

25 2 N l T f ti25 2 N l T f ti > S

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a. ?ultiply the half8life of car'on81$ 'y

the total nu!'er of half8lives.

Calculate Sole for the un/no0ns.2

Sam'lePro'le! 25.1

t nG 5" years " G 1,17 years12

25 2 N l T f ti >25 2 N l T f ti > S l P 'l 25 1

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Sam'lePro'le! 25.1

$. )he initial !ass of car'on81$ is

reduced 'y one8half for each half8life.

+o, !ultiply 'y three ti!es.12

Re!aining !ass G 2. 1912g 12

12

12

G .25 1912g

G 2.5 191"g

25 2 N l T f ti >25 2 N l T f ti > S l P 'l 25 1

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Sam'lePro'le! 25.1

$. %ou can get the sa!e ans(er 'y

using the euation for an e/ponential

decay function.

G 42. 1912g6

G .25 1912g

G 2.5 191"g

AG A G 42. 1912g64 612

n 4 612"

4 61

3

25 2 N l T f ti >25 2 Nuclear Transformations > S l P 'l 25 1

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Ealuate&o the results ma/e sense?

9

Sam'lePro'le! 25.1

0 )he !ass of car'on81$ after three half8lives

should 'e one8eighth of the original !ass.

0 If you divide 2.5 191"g 'y 2. 1912g,you (ill get 12.5H, or .13

25 2 N l T f ti >25 2 Nuclear Transformations >

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The half,life of 'hos'horus,92 is8:.9 da%s. Ho0 man% milli(rams of

'hos'horus,92 remain after 844.8

da%s if %ou $e(in 0ith 2.5 m( of theradioisoto'e?

25 2 Nuclear Transformations >25 2 Nuclear Transformations >

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The half,life of 'hos'horus,92 is8:.9 da%s. Ho0 man% milli(rams of

'hos'horus,92 remain after 844.8

da%s if %ou $e(in 0ith 2.5 m( of theradioisoto'e?

nG 1.1 days G half8lives1 half8life

1$." days

G 42.5 !g6 G 2. 192!g

AG A G 42.5 !g64 612

n 4 612

4 6 1123

25 2 Nuclear Transformations >25 2 Nuclear Transformations > )rans!utation Reactions)rans!utation Reactions

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)rans!utation Reactions)rans!utation Reactions

Transmutation Reactions

-hat are t(o (ays in (hich

trans!utation can occur


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#or thousands of years, alche!ists tried

to change lead into gold.

0 -hat they (anted to achieve is

transmutation, or the conversion of an ato!

of one ele!ent into an ato! of another

ele!ent.


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)rans!utation can occur 'y radioactive

decay, or (hen particles 'o!'ard the

nucleus of an ato!.0 )he particles !ay 'e protons, neutrons,

alpha particles, or s!all ato!s.


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Ernst Rutherford perfor!ed the earliest

artificial trans!utation in 1717.

0 @e 'o!'arded nitrogen gas (ith alpha

particles.

0 )he unsta'le fluorine ato!s uic*ly decay tofor! a sta'le isotope of o/ygen and a proton.

< :1

3 p1

1#13

7

Proton25 2 Nuclear Transformations > )rans!utation Reactions)rans!utation Reactions

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RutherfordFs e/peri!ent eventually led to

the discovery of the proton.

0 @e and other scientists noticed a pattern as they did

different trans!utation e/peri!ents. @ydrogen nuclei(ere e!itted.

0 +cientists realied that these hydrogen nuclei 4protons6

!ust have a funda!ental role in ato!ic structure.

@e

Alphaparticle

itrogenato!

#

Dnsta'lefluorine ato!


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a!es Chad(ic*Fs discovery of theneutron in 17"2 also involved a

trans!utation e/peri!ent.

0 eutrons (ere produced (hen 'erylliu!87

(as 'o!'arded (ith alpha particles.

C :12

n1

eutronCar'on812

>e :7

$ @e$

2

>erylliu!87 Alphaparticle


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Ele!ents (ith ato!ic nu!'ers a'ove 72,the ato!ic nu!'er of uraniu!, are called

transuranium elements.

0 one of these ele!ents occurs in nature.

0 All of the! are radioactive.

0 All transuraniu! ele!ents undergotrans!utation.


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)ransuraniu! ele!ents are synthesied in nuclear

reactors and nuclear accelerators.0 Reactors produce 'ea!s of lo(8

energy particles.

0 Accelerators are used to increase

the speed of 'o!'arding

particles to very high speeds.

9 )he European

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0 -hen uraniu!82"3 is 'o!'arded (ith the relatively

slo( neutrons fro! a nuclear reactor, so!e uraniu!nuclei capture these neutrons. )he product is uraniu!8

2"7.

0 Draniu!82"7 is radioactive and e!its a 'eta particle.)he other product is an isotope of the artificial

radioactive ele!ent neptuniu! 4ato!ic nu!'er 7"6.

0 eptuniu! is unsta'le and decays, e!itting a 'eta

particle and a second artificial ele!ent, plutoniu!

4ato!ic nu!'er 7$6.

p :2"7

7" e

91D2"7

72

D :2"3

72 n1

D2"7

72

Pu :2"7

7$ e

91p2"7

7"


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+cientists in >er*eley, California,synthesied the first t(o artificial ele!ents

in 17$.

0 +ince that ti!e, !ore than 2 additionaltransuraniu! ele!ents have 'een produced

artificially.


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Which of the follo0in( al0a%s chan(es

0hen transmutation occurs?

*. )he nu!'er of electrons

+. )he !ass nu!'er

C. )he ato!ic nu!'er

&. )he nu!'er of neutrons


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Which of the follo0in( al0a%s chan(es

0hen transmutation occurs?

*. )he nu!'er of electrons

+. )he !ass nu!'er

C. The atomic num$er

&. )he nu!'er of neutrons

25 2 Nuclear Transformations >25 2 Nuclear Transformations > Jey ConceptsJey Concepts

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Jey ConceptsJey Concepts

The neutron,to,'roton ratio in aradioisoto'e determines the t%'e of deca%

that occurs.

*fter each half,life) half of the ori(inalradioactie atoms hae deca%ed into atoms

of a ne0 element.

Transmutation can occur $% radioactiedeca%) or 0hen 'articles $om$ard the

nucleus of an atom.

25 2 Nuclear Transformations >25.2 Nuclear Transformations > Jey EuationJey Euation

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Jey EuationJey Euation

AG A1

2

n

25 2 Nuclear Transformations >25.2 Nuclear Transformations > Blossary )er!sBlossary )er!s

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Blossary )er!sBlossary )er!s

0 nuclear force;an attractive force that acts'et(een allnuclear particles that are

e/tre!ely close together, li*e protons and

neutrons in a nucleus

0 $and of sta$ilit%;the location of sta'le nuclei

on a neutron8vs.8proton plot

0 'ositron;a particle (ith the !ass of anelectron 'ut a positive charge

25.2 Nuclear Transformations >25.2 Nuclear Transformations > Blossary )er!sBlossary )er!s

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25.2 Nuclear Transformations >25.2 Nuclear Transformations


Blossary )er!sBlossary )er!s

0 half,life;the ti!e reuired for one8half of thenuclei of a radioisotope sa!ple to decay to

products

0 transmutation;the conversion of an ato! ofone ele!ent to an ato! of another ele!ent

0 transuranium elements;any ele!ents in the

periodic ta'le (ith ato!ic nu!'er a'ove 72,the ato!ic nu!'er of uraniu!

25.2 Nuclear Transformations >25.2 Nuclear Transformations > +I

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25.2 Nuclear Transformations >25.2 Nuclear Transformations


Electrons and the Structure of *toms

0 Dnsta'le ato!ic nuclei decay 'y e!itting

alpha or 'eta particles.

0 25.2 Nuclear Transformations >

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25.2 Nuclear Transformations 25.2 Nuclear Transformations

EN& " 25.2EN& " 25.2

ch25 lesson25_2

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