by: Kerem ERYILMAZ

Adnan ÖZTÜREL

Chemical reactions all involve the exchange or sharing of electrons, they never have an influence on the nucleus of the atom.  Nuclear reactions involve a change in the nucleus.  There are forces in the nucleus that oppose each other, the "Strong" force holding Protons and Neutrons to each other and the electrostatic force of protons repelling other protons.  Under certain arrangements of protons and neutrons the electrostatic force can cause instability in the nucleus causing it to decay. It will continue to decay until it reaches a stable combination.

Nuclear Reactions

This graph shows the stable nuclei in red.  There are several things to notice:

- There are no stable nuclei with an atomic number higher than 83 or a  neutron number higher than 126. - The more protons in the nuclei, the more neutrons are needed for stability.  Notice how the stability band pulls away from the P=N line. - Stability is favored by even numbers of protons and even numbers of neutrons. 168 of the stable nuclei are even-even while only 4 of the stable nuclei are odd-odd.

Unstable nuclei, called radioactive isotopes, will undergo nuclear decay as it becomes more stable.  There are only certain types of nuclear decay which means that most isotopes can't jump directly from being unstable to being stable.  It often takes several decays to eventually become a stable nuclei.  

Types of Radioactive Decay 

When unstable nuclei decay, the reactions generally involve the emission of a particle and or energy.  Below is a table describing the types of nuclear decay. Notice that for each type of decay, the equation is balanced with regard to atomic number and atomic mass. In other words, the total atomic number before and after the reaction are equal.  And the total atomic mass before and after the reaction are also equal.

Particle Name

alpha particles

What is it?

helium nuclei                or             

Relative penetrating power1 stopped by the skin but very damaging due to ionization

Happens to nuclei with  Z>83

The 2 p+ 2n loss brings the atom downand to the left toward the belt of stable nuclei.

Particle Name

What is it?

Relative penetrating power

beta particles

high speed electron              or               

100 penetrates human tissue to ~1cm 

Happens to nuclei with high neutron:proton ratio

A neutron becomes a proton causing a shift down and to the right on the stability graph  

Particle Name

What is it?

Relative penetrating power

gamma rays

high energy photon

             

10000highly penetrating but not very ionizing

Generally accompanies other radioactive radiation because it is the energy lost from settling within the nucleus after a change. Since gamma rays do not affect the atomic number or mass number, it is generally not shown in the nuclear equation.

Particle Name

What is it?

Relative penetrating power

positron emission

positron

          

100

Happens to nuclei with a low neutron:proton ratio

A proton becomes a neutron causing a shift up and to the left

Particle Name

What is it?

Relative penetrating power

electron capture

inner shell electron

            

 no release of energy or particle

Happens to nuclei with a low neutron: proton ratio

A proton becomes a neutron causing a shift up and to the left.  Always results in gamma radiation

This graph shows all the trends of decay and the band of stable nuclei.  There are some exceptions to the trends but generally a nuclei will decay following the trends (in multiple steps) until it becomes stable.  For example

92U238 will go through 8 alpha emissions and 6 beta emissions (not all in order) before becoming 82Pb206

The steps a nuclei follows in becoming stable is called a radioactive series.  The series for 92U238 is shown below as an example.

Z > 83 --  alpha 92U 238 => 90Th234 + 2He4  

unpredicted Beta 90Th234 =>  91Pa234 + -1eo 

unpredicted  Beta 91Pa234 =>  92U234 + -1e

o

Z > 83 --  alpha 92U234 => 90Th230 + 2He4

Z > 83 --  alpha 90Th230 => 88Ra226 + 2He4

Z > 83 --  alpha 88Ra226 => 86Rn222 + 2He4 

Z > 83 --  alpha 86Rn222 => 84Po218 + 2He4 

Z > 83 --  alpha 84Po218 => 82Pb214 + 2He4 

Beta 82Pb214 => 83Bi214 + -1eo 

Beta 83Bi214 => 84Po214 + -1eo 

Z > 83 --  alpha 84Po214 => 82Pb210 + 2He4 

Beta  82Pb210 => 83Bi210 + -1eo 

Beta 83Po210 => 84Po210 + -1eo

Z > 83 --  alpha 84Po210 => 82Pb206 + 2He4 

stable  82Pb206

Differences Between Nuclear and Chemical Reactions

Six Differences between nuclear reactions and chemical reactions.

Nuclear Reactions Chemical Reactions 1. Protons and neutrons react 1. Electrons react outside nucleus.

inside nucleus.

2. Elements transmute into other 2. The same number of each kind of elements. atom appear in the reactants

and products.

3. Isotopes react differently. 3. Isotopes react the same.

4. Independent of chemical 4. Depend on chemical combination. combination.

5. Energy changes equal 10^8 kJ. 5. Energy changes equal 10 - 10^3 kJ/mol.

6. Mass changes are detectable. 6. Mass reactants = mass products.