Nuclear Chemistry

NUCLEAR CHEMISTRYChapter 25

Introduction to Nuclear Chemistry Nuclear chemistry is the study of the

structure of and the they undergo.

Chemical vs. Nuclear ReactionsChemical Reactions Nuclear Reactions

Occur when bonds are broken

Occur when nuclei emit particles and/or rays

Chemical vs. Nuclear ReactionsChemical Reactions Nuclear ReactionsOccur when bonds are broken Occur when nuclei emit particles

and/or rays

Atoms remain unchanged, although they may be rearranged

Atoms often converted into atoms of another element

Chemical vs. Nuclear ReactionsChemical Reactions Nuclear ReactionsOccur when bonds are broken Occur when nuclei emit particles

and/or raysAtoms remain unchanged, although they may be rearranged

Atoms often converted into atoms of another element

Involve only valence electrons

May involve protons, neutrons, and electrons

Chemical vs. Nuclear ReactionsChemical Reactions Nuclear ReactionsOccur when bonds are broken Occur when nuclei emit particles

and/or raysAtoms remain unchanged, although they may be rearranged

Atoms often converted into atoms of another element

Involve only valence electrons May involve protons, neutrons, and electrons

Associated with small energy changes

Associated with large energy changes

Chemical vs. Nuclear ReactionsChemical Reactions Nuclear ReactionsOccur when bonds are broken Occur when nuclei emit particles

and/or raysAtoms remain unchanged, although they may be rearranged

Atoms often converted into atoms of another element

Involve only valence electrons May involve protons, neutrons, and electrons

Associated with small energy changes

Associated with large energy changes

Reaction rate influenced by temperature, particle size, concentration, etc.

Reaction rate is not influenced by temperature, particle size, concentration, etc.

The Discovery of Radioactivity (1895 – 1898): found that invisible rays

were emitted when electrons bombarded the surface of certain materials.

Becquerel accidently discovered that phosphorescent salts produced spontaneous emissions that darkened photographic plates

The Discovery of Radioactivity (1895 – 1898): isolated the components (

atoms) emitting the rays – process by

which particles give off – the penetrating

rays and particles by a radioactive source

The Discovery of Radioactivity (1895 – 1898): identified 2 new elements,

and on the basis of their radioactivity

These findings Dalton’s theory of indivisible atoms.

The Discovery of Radioactivity (1895 – 1898): – atoms of the

element with different numbers of

– isotopes of atoms with nuclei (too / neutrons)

– when unstable nuclei energy by emitting to attain more atomic configurations ( process)

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

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Beta radiation Composition – Beta particles, same as an

electron Symbol – e-, β Charge – 1- Mass (amu) – 1/1837 (practically 0) Approximate energy – 0.05 – 1 MeV Penetrating power – moderate (4 mm

body tissue) Shielding – metal foil

Gamma radiation Composition – High-energy

electromagnetic radiation Symbol – γ Charge – 0 Mass (amu) – 0 Approximate energy – 1 MeV Penetrating power – high (penetrates

body easily) Shielding – lead, concrete

Review of Atomic StructureNucleus Electrons

99.9% of the mass1/10,000 the size of the atom

0.01% of the mass

Review of Atomic StructureNucleus Electrons99.9% of the mass1/10,000 the size of the atom

0.01% of the mass

Composed of protons (p+) and neutrons (n0)

Composed of electrons (e-)

Review of Atomic StructureNucleus Electrons99.9% of the mass1/10,000 the size of the atom

0.01% of the mass

Composed of protons (p+) and neutrons (n0)

Composed of electrons (e-)

Positively charged

Negatively charged

Review of Atomic StructureNucleus Electrons99.9% of the mass1/10,000 the size of the atom

0.01% of the mass

Composed of protons (p+) and neutrons (n0)

Composed of electrons (e-)

Positively charged Negatively charged

Strong nuclear force (holds the nucleus together)

Weak electrostatic force (because they are charged negatively

Chemical Symbols A chemical symbol looks like…

To find the number of , subtract the from the

C614

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

Nuclear Stability Elements with atomic #s to are

.

ratio of protons:neutrons (p+ : n0) Example: Mercury – 200 has

protons and neutrons

Nuclear Stability Elements with atomic #s are and . Examples: and

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 element. All nuclear equations are .

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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.

Mass #

Atomic #

Step 2: Draw the arrow.

Step 3: Write the alpha particle.Step 4: Determine the other product (ensuring everything is balanced).

Alpha Decay Example 2: Write the nuclear equation

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

Mass #

Atomic #

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 .

0-1

Beta Decay Example 1: Write the nuclear equation

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

Mass #

Atomic #

Beta Decay Example 2: Write the nuclear equation

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

Mass #

Atomic #

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.

Transmutation –

the of one atom of one element to an atom of a different element ( decay is one way that this occurs!)

ReviewType of

Radioactive

Decay

Particle

Emitted

Change in Mass

#

Change in

Atomic #

Alpha α He

-4 -2

Beta β e 0 +1Gamma γ 0 0

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-1

Half-Life is the required

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

For any radioisotope,# of ½ lives % Remaining0 100%1 50%2 25%3 12.5%4 6.25%5 3.125%6 1.5625%

Half-Life

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 0 101 29 52 58 2.53 87 1.254 116 0.625

Half-Life Or an equation!

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? ________ 2 half lives? __________ 3 half lives? __________

Half-Life Example 2: 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 3: 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 4: 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 5: 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 Reactions Characteristics: Isotopes of one element are

into isotopes of another element Contents of the change amounts of are

released

Types of Nuclear Reactions

decay – alpha and beta particles and gamma ray emission

Nuclear - emission of a or

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).

Nuclear Fission - 1st controlled nuclear reaction in

December 1942. 1st uncontrolled nuclear explosion occurred July 1945.

- Examples – atomic bomb, current nuclear power plants

Nuclear Fusion - of a nuclei - Two nuclei combine to form a

heavier nucleus - Does not occur under standard conditions

( repels ) - Advantages compared to fission -

,

- Disadvantages - requires amount of energy to , difficult to

- Examples – energy output of stars, hydrogen bomb, future nuclear power plants