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NUCLEAR CHEMISTRY

Unit 15

Introduction to Nuclear Chemistry

Nuclear chemistry is the study of the structure of

atomic nuclei and the changes they undergo.

Characteristics of nuclear reactions:

Isotopes of one element are changed into isotopes of

another element

Contents of the nucleus change

Large amounts of energy are released

Chemical vs. Nuclear Reactions

Chemical Reactions Nuclear Reactions

Bonds are broken Nuclei emit particles

and/or rays



Bonds are broken Nuclei emit particles and/or rays

Atoms are

rearranged

Atoms changed into

atoms of another

element




Atoms may be rearranged Atoms changed to atoms of a different

element

Involve valence

electrons from

electron cloud

Involve protons,

neutrons, and/or

electrons from

nucleus




Atoms are rearranged Atoms change into atoms of a different

element

Involve valence electrons from electron

cloud

Involve protons, neutrons, and/or electrons

from nucleus

Small energy

changes

Large energy

changes




Atoms are rearranged Atoms change into atoms of a different

element

Involve valence electrons from electron

cloud

Involve protons, neutrons, and/or electrons

from nucleus

Small energy changes Large energy changes

Radioactivity

Radioactivity– process by which atoms give off rays

or particles

Radiation– the penetrating rays and particles

emitted by a radioactive source

The Discovery of Radioactivity (1895 –

1898):

Roentgen found that invisible rays were emitted when electrons hit the surface of a fluorescent screen (discovered x-rays)

Becquerel accidently discovered that phosphorescent uranium rock produced spots on photographic plates (discovered radioactivity)

Marie and Pierre Curie:

isolated the components emitting the rays (uranium atoms)

identified 2 new elements, polonium and radium on the basis of their radioactivity

These findings contradicted Dalton’s theory of indivisible atoms.

Review of Atomic Structure

Nucleus Electron Cloud

Majority of the mass

of the atom (99.9%)

None of the volume

of the atom (0.01%)

None of the mass of

the atom (0.01%)

Majority of the

volume of the atom

(9,999 times the size

of the nucleus)


Nucleus Electron Cloud

Majority of the mass of the atom (99.9%)

None of the volume of the atom (0.01%)

None of the mass of the atom (0.01%)

Majority of the volume of the atom (9,999

times the size of the nucleus)

Protons (p+) and

neutrons (n0)

Electrons (e-)


Nucleus Electron cloud






Protons (p+) and neutrons (n0) Electrons (e-)

Positively charged Negatively charged


Nucleus Electron cloud






Protons (p+) and neutrons (n0) Electrons (e-)

Positively charged Negatively charged

Strong nuclear force

holds the protons

together

Weak electrostatic

force between

negatively charged

electrons and positively

charged nucleus

nucleons – particles found in the nucleus

Neutrons and protons

The nuclear symbol consists of three parts:

Element symbol

atomic number (Z) – number of protons in the

nucleus

mass number (A) – sum of the number of protons

and neutrons

Also written as the element name dash (-) mass

number (example: Carbon- 12)

nuclide – each unique atom

Ion- an atom with a charge

A Review of Atomic Terms

Radioactivity:

Isotopes– atoms of the same element with different

numbers of neutrons

Radioisotopes– isotopes of atoms with unstable

nuclei (too many or too few neutrons)

Radioactive decay– when unstable nuclei lose

energy by emitting radiation to become more

stable

This is a spontaneous reaction (happens on its own)

Nuclear Stability

Generally elements with atomic #s 1 to 20 are very

stable.

Isotope is completely stable if the nucleus will not

spontaneously decompose.

1:1ratio of protons : neutrons (p+; n0)

Example: Carbon – 12 has 6 protons and 6 neutrons

Nuclear Stability

Generally elements with atomic #s 21to 83 are

marginally stable.

1:1.5 ratio of protons:neutrons (p+:n0)

Example: Mercury – 200 has 80 protons and 120

neutrons

Nuclear Stability

Generally elements with atomic #s > 83 are

unstable and radioactive.

Examples: Uranium and Plutonium

Nuclear Reactions

Types of Nuclear Reactions:

Radioactive decay – alpha and beta particles and

gamma ray emission

Nuclear disintegration - emission of a proton or neutron

Transmutation the conversion of an atom of one

element to an atom of a different element.

Usually occurs by radioactive decay

Nuclear Equation

Nuclear equation – shows the radioactive

decomposition of an element

Alpha radiation

Composition – Alpha particles, same as a helium nuclei

Symbol – Helium nuclei, He, α

Charge – 2+

Deflected towards a negatively charged plate

Mass – 4 amu

Approximate energy – 5.0 MeV

Penetrating power – low (0.05 mm body tissue)

Shielding – paper, clothing

42

Alpha Decay

Example 1: Write the nuclear equation for the radioactive decay of polonium – 210 by alpha emission.

Mass #

Atomic #

Step 1: Write the nuclear symbol for the element that you are

starting with followed by the yields symbol.

Step 2: Write the alpha particle as a product

Step 3: Determine the other product using atomic #.

Step 4: Determine mass and ensure everything is balanced.(Net effect is loss of 4 in mass number and loss of 2 in atomic number.)

Alpha Decay

Example 2: Write the nuclear equation for the

radioactive decay of radium – 226 by alpha

emission.

Beta radiation

Composition – Beta particles, same as a fast moving electron

A neutron is converted to a proton and a beta particle.

Symbol – −10𝑒, 0-1β

Charge – 1-

Deflected towards a positively charged plate

Mass (amu) – 1/1837 (practically 0)

Approximate energy – 0.05 – 1 MeV

Penetrating power – moderate (4 mm body tissue)

Shielding – metal foil

Beta Decay


radioactive decay of carbon – 14 by beta emission.

Steps: same steps as alpha equations except use a

beta particle(Net effect is no change in mass and addition of 1 in

atomic number.)

Beta Decay


radioactive decay of zirconium – 97 by beta

decay.

Gamma radiation

Composition – gamma ray, High-energy electromagnetic radiation or high energy photon

Usually accompanied by alpha and beta radiation

Symbol – ooγ or γ

Charge – 0

Mass (amu) – 0

Approximate energy – 1 MeV

Penetrating power – high (penetrates body easily)

Shielding – lead, concrete, water

Gamma Decay


radioactive decay of uranium – 238 by gamma

decay accompanied with alpha decay.

Steps: include alpha and/or beta, and gamma decay

Radioactive Decay

Review

Type of

Radioactive

Decay

Particle

Emitted

Change in

Mass #

Change in

Atomic #

Alpha α He -4 -2

Beta β e 0 +1

Gamma γ 0 (plus

alpha

and/or

beta

decay)

0 (plus

alpha

and/or

beta

decay)

42

0-1

Radioactive Decay

Decay series:

when a substance

undergoes a series

of nuclear decay

Half-Life

Half-life is the time required for half 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%

Half-Life

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7

% R

em

ain

ing

# of Half-Lives

Half-Life

Half-Life

Example 6: suppose you have 10.0 grams of

strontium – 90, which has a half life of 29 years.

How much will be remaining after 116 number of

years?

You can use a table:

# of ½ lives Time (Years) Amount

Remaining (g)

0 0 10

1 29 5

2 58 2.5

3 87 1.25

4 116 0.625

Half-Life

Or an equation!

Half-Life

Example 7: 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? ________

2 half lives? __________ 3 half lives? __________

Half-Life

Example 8: Cobalt – 60, with a half-life of 5 years,

is used in cancer radiation treatments. If a hospital

purchases a supply of 30.0 g, how much would be

left after 15 years? ______________

Half-Life

Example 9: Iron-59 is used in medicine to diagnose

blood circulation disorders. The half-life of iron-59

is 44.5 days. How much of a 2.000 mg sample will

remain after 133.5 days? ______________

Half-Life

Example 10: The half-life of polonium-218 is 3.0

minutes. If you start with 20.0 g, how long will it

take before only 1.25 g remains? ______________

Half-Life

Example 11: A sample initially contains 150.0 mg

of radon-222. After 11.4 days, the sample

contains 18.75 mg of radon-222. Calculate the

half-life.

Nuclear Fission

Nuclear Fission- splitting of a nucleus

Releases a lot of energy

Chain reactions occur

Produces radioactive waste

Usually fueled by Uranium

Example: atomic bomb, nuclear reactors, nuclear

power plants

Fission

Nuclear Fusion

Nuclear Fusion- combining of two or more nuclei

Two light nuclei combine to form a single heavier nucleus

Does not occur under standard conditions

Releases a lot of energy (more than fission)

Not radioactive

Can cause chain reactions

Usually fueled by isotopes of hydrogen

Example: energy output of stars (and the sun) and

hydrogen bomb (more powerful than atomic bombs)

Fusion

Advantages and Disadvantages

Advantages

Fission Fusion

• Zero air pollution

• Not a fossil fuel so doesn’t contribute to

climate change

• Able to be controlled

• No radioactive waste

• Inexpensive

Disadvantages

Fission Fusion

• Produces high level radioactive waste

that must be stored for 10,000’s of

years.

• Meltdown causes disasters like in Japan

and Chernobyl.

• Requires large amount of energy to

start

• Difficult to control

Uses of Radiation

Radioactive dating

Detection of diseases

Treatment of some malignant tumors

X-rays

Radioactive tracers

Everyday items: thorium–232 used in lantern mantels, plutonium–238 used in long-lasting batteries for space, and americium–241 in smoke detectors.

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