Nuclear chemistry power point.pptx

(1)

NUCLEAR CHEMISTRY

(2)

Introduction to Nuclear Chemistry

 Nuclear chemistry is the study of the

structure of and the

they undergo.

(3)

Chemical vs. Nuclear Reactions

Chemical Reactions Nuclear Reactions

Bonds are

broken

Nuclei emit

particles and/or

(4)

Chemical Reactions Nuclear Reactions

Bonds are broken Nuclei emit particles and/or rays

Atoms are

(5)

Chemical Reactions Nuclear Reactions

Bonds are broken Nuclei emit particles and/or rays Atoms may be rearranged Atoms changed to atoms of

different element

Involve valence

(6)

Chemical Reactions Nuclear Reactions

Bonds are broken Nuclei emit particles and/or rays Atoms are rearranged Atoms change into atoms of

different element

Involve valence electrons Involve protons, neutrons, and/or electrons

Small energy

(7)

Chemical Reactions Nuclear Reactions

Bonds are broken Nuclei emit particles and/or rays Atoms are rearranged Atoms change into atoms of

different element

Involve valence electrons Involve protons, neutrons, and/or electrons

Small energy changes Large energy changes

Reaction rate can

(8)

The Discovery of Radioactivity (1895 –

1898):

 found that invisible rays

were emitted when electrons hit the surface of a fluorosent screen

(discovered x-rays)

 Becquerel accidently discovered that

phosphorescent rock

produced spots on photographic plates

Roentgen

(9)

The Discovery of Radioactivity (1895 – 1898):



 isolated the components (

atoms) emitting the rays

 – process by

which atoms give off

 – the penetrating

rays and particles by a radioactive source

Marie and Pierre

Curie

uranium

Radioactivity

rays or particles

Radiation

(10)

 identified 2 new elements,

and on the basis of their radioactivity

 These findings

Dalton’s theory of indivisible atoms.

polonium

radium

contradi

cted

(11)

 – atoms of the same

element with different numbers of

 – isotopes of

atoms with unstable nuclei (too many or too few neutrons)

 – when

unstable nuclei lose energy by emitting to become more

Isotopesneutrons

Radioisotopes

Radioactive decay

radiation

stable

(12)

Alpha radiation

 Composition – Alpha particles, same as

helium nuclei

 Symbol – Helium nuclei, He, α  Charge – 2+

 Mass (amu) – 4

 Approximate energy – 5 MeV

 Penetrating power – low (0.05 mm body

tissue)

 Shielding – paper, clothing

(13)

Beta radiation

 Composition – Beta particles, same as an

electron

 Symbol – e-, 0

-1β

 Charge –

1- Mass (amu) – 1/1837 (practically 0)  Approximate energy – 0.05 – 1 MeV

 Penetrating power – moderate (4 mm body

tissue)

(14)

Gamma radiation

 Composition – High-energy

electromagnetic radiation

 Symbol – o

oγ

 Charge – 0

 Mass (amu) – 0

 Approximate energy – 1 MeV

 Penetrating power – high (penetrates body

easily)

(15)

Review of Atomic Structure

Nucleus Electron Cloud

99.9% of the

mass

1/10,000 the

size of the atom

0.01% of the

mass 9,999

(16)

Nucleus Electron Cloud

99.9% of the mass

1/10,000 the size of the atom 0.01% of the mass, 9,999 times the size of the nucleus

Protons (p

+

) and

neutrons (n

0

)

(17)

Nucleus Electrons

99.9% of the mass

1/10,000 the size of the atom 0.01% of the mass, 9,999 times the size of the nucleus Protons (p+) and neutrons (n0) Electrons (e-)

Positively

(18)

Nucleus Electrons

99.9% of the mass

1/10,000 the size of the atom 0.01% of the mass, 9,999 times the size of the nucleus Protons (p+) and neutrons (n0) Electrons (e-)

Positively charged Negatively charged

Strong nuclear

force (holds the

protons

together)

Weak

electrostatic

(19)

Chemical Symbols

A chemical symbol looks like…

p+ = e- = atomic #

To find the number of , subtract the

from the

C

6 14

mass #

atomic #

mass #

(20)

Nuclear Stability

 Isotope is completely stable if the

nucleus will spontaneously .

 Elements with atomic #s to are

.

 ratio of protons:neutrons (

)

 Example: Carbon – 12 has protons

and neutrons

not

decompose

20

1

very stable

1:1

p

+

:n

0

(21)

Nuclear Stability

 Elements with atomic #s to are

.

 ratio of protons:neutrons (p+ : n0)

 Example: Mercury – 200 has

protons and neutrons

21 83

marginally stable

1:1.5

(22)

Nuclear Stability

 Elements with atomic #s are

and .

 Examples: and

> 83

(23)

Alpha Decay

 Alpha decay – emission of an alpha

particle ( ), denoted by the symbol , because an α has 2 protons and 2

neutrons, just like the He nucleus. Charge is because of the 2 .

 Alpha decay causes the number

to decrease by and the number to decrease by .

 determines the

(24)

Alpha Decay

 Example 1: Write the nuclear equation

for the radioactive decay of polonium – 210 by alpha emission.

Step 1: Write the element that you are

starting with.

210

Po

84

Mass # Atomic #

Step 2: Draw the arrow.

Step 3: Write the alpha particle.

Step 4: Determine the other product

(ensuring everything is balanced).

(25)

Alpha Decay

for the radioactive decay of radium – 226 by alpha emission.

starting with.

226

Ra

88

Mass # Atomic #

Step 3: Write the alpha particle.

Step 4: Determine the other product

(26)

Beta decay

 Beta decay – emission of a beta particle (

), a fast moving , denoted by the symbol or . β has insignificant mass ( ) and the charge is because it’s an .

 Beta decay causes change in

number and causes the number to increase by .

 A neutron is converted to a proton and a

beta particle.

β

0

electron

-1

no

mass

1

atomic

electron

e

-e

(27)

Beta Decay

for the radioactive decay of carbon – 14 by beta emission.

starting with.

14

C

6

Mass # Atomic #

Step 3: Write the beta particle.

Step 4: Determine the other product

0

e

-1

14

N

(28)

Beta Decay

for the radioactive decay of zirconium – 97 by beta decay.

starting with.

97

Zr

40

Mass # Atomic #

Step 3: Write the beta particle.

Step 4: Determine the other product

0

e

-1

97

Nb

(29)

Gamma decay

 Gamma rays – high-energy

radiation, denoted by the symbol .

 γ has no mass ( ) and no charge ( ).

Thus, it causes change in or numbers. Gamma rays almost

accompany alpha and beta radiation. However, since there is effect on

mass number or atomic number, they are usually from nuclear equations.

electromagnetic

γ

0

no

mass

atomic

always

no

(30)

Transmutation



the of an atom of one element to an atom of a different element.

Radioactive decay is one way

that this occurs!

(31)

Review

Type of

Radioact

ive

Decay

Particl

e

Emitte

d

Change

in Mass

#

Change

in

Atomic

#

Alpha

α

He

-4

-2

Beta

β e

0

+1

Gamma

γ

0

(32)

Half-Life

 is the required

for of a radioisotope’s nuclei to decay into its products.

 For any radioisotope,_{# of ½ lives} _{% Remaining}

0 100%

1 50%

2 25%

3 12.5%

4 6.25%

5 3.125%

6 1.5625%

(33)

Half-Life

0 1 2 3 4 5 6 7

0 10 20 30 40 50 60 70 80 90 100 Half-Life

# of Half-Lives

(34)

Half-Life

 For example, suppose you have 10.0

grams of strontium – 90, which has a half life of 29 years. How much will be

remaining after x number of years?

 You can use a table:

# of ½ lives

Time (Years)

Amount Remaining (g)

0

10

1

29

5

2

58

2.5

3

87

1.25

(35)

Half-Life

 Or an equation!

m

t

= m

₀

x (0.5)

n

mass remaining

initial mass

(36)

Half-Life

 Example 1: If gallium – 68 has a half-life

of 68.3 minutes, how much of a 160.0 mg sample is left after 1 half life?

________

(37)

Half-Life

 Example 2: Cobalt – 60, with a half-life of

5 years, is used in cancer radiation treatments. If a hospital purchases a

(38)

Half-Life

 Example 3: Iron-59 is used in medicine

(39)

Half-Life

 Example 4: The half-life of polonium-218

(40)

Half-Life

 Example 5: A sample initially contains

(41)

Nuclear Reactions

 Characteristics:

 Isotopes of one element are

into isotopes of another element

 Contents of the change

 amounts of are

released

changed

nucleus

(42)

Types of Nuclear Reactions

 decay – alpha and

beta particles and gamma ray emission

 Nuclear -

emission of a or

Radioactive

disintegration

neutron

(43)

Nuclear Fission

 - of a nucleus

 - Very heavy nucleus is split into

approximately fragments

 - reaction releases several neutrons

which more nuclei

 - If controlled, energy is released

(like in ) Reaction control depends on reducing the of the neutrons (increases the reaction rate) and extra neutrons ( creases the reaction

rate).

Fissionsplitting

slowly

split

Chain

equal

two

nuclear reactors

speed

(44)

Nuclear Fission

 - 1st controlled nuclear reaction in

December 1942. 1st uncontrolled

nuclear explosion occurred July 1945.

 - Examples – atomic bomb, current

(45)

Nuclear Fission

 Disadvantages

 Produces high level radioactive waste that must be stored for 10,000’s of years.

 Meltdown causes disasters like in Japan and Chernobyl.

 Advantages

 Zero air pollution

(46)

Nuclear Fusion

 - Fusion: Combining of two nuclei

 - Two light nuclei combine to form a single

heavier nucleus

 - Does not occur under standard conditions

(positive nuclei repel each other)

 - Advantages compared to fission – No

radioactive waste, inexpensive ,

 - Disadvantages - requires large amount of

energy to start, difficult to control.

 - Examples – energy output of stars, hydrogen

(47)

Uses of Radiation

 Radioactive dating: Carbon–14 used to

determine the age of an object that was once alive.

 Detection of diseases: Iodine–131 used to

detect thyroid problems, technetium–99 used to detect cancerous tumors and brain disorders, phosphorus – 32 used to detect stomach cancer.  Treatment of some malignant tumors

(cobalt–60 and cesium–137) cancer cells are

(48)

Uses of Radiation

 X-rays

 Radioactive tracers: used in research

to tag chemicals to follow in living organisms

 Everyday items: thorium–232 used in

lantern mantels, plutonium–238 used in long-lasting batteries for space, and