1. Nuclear Chemistry

2. Radioactivity
Nuclear Reactions – reactions in which the nuclei of unstable isotopes (radioisotopes) gain stability by undergoing changes

3. Radioactivity
Henri Becquerel noticed that uranium ore exposed photographic film
Marie & Pierre Curie named the process radioactivity
The particles and rays emitted by a radioactive source are called radiation

4. Radioactivity
Radioactivity disproves Dalton’s theory of indivisible atoms
The stability of a nucleus depends on the relative proportion of neutrons to protons in the nucleus as well as the overall size of the nucleus
An unstable nucleus loses energy by emitting radiation during the process of radioactive decay

5. Types of Radiation
Alpha Radiation – consists of helium nuclei emitted from a radioactive source (alpha particles).
In nuclear equations, an alpha particle is written as

6. Types of Radiation
Beta Radiation – fast moving electrons formed by the decomposition of a neutron in an atom (beta particles)
In nuclear equations, beta particles are written as

7. Types of Radiation
Gamma Radiation – high energy electromagnetic radiation given off by a radioisotope
Often emitted along with alpha or beta radiation by the nuclei of disintegrating radioactive atoms

8. Types of Radiation Property Alpha Rad Beta Rad Gamma Rad Composition
Alpha Particle
Beta Particle
Gamma Ray
Symbol
Charge 2+ 1-
Mass 4
1/1837
Shielding
Paper, clothing
Metal foil
Lead, concrete

9. Nuclear Stability and Decay
1500 nuclei are known. Of those, only 264 are stable and do not decay with time
In elements of low atomic number (less than 20), stable nuclei have roughly equal n0 and p+
In elements of high atomic number, stable nuclei have more n0 than p+

10. Nuclear Stability and Decay
The stable nuclei on a neutron vs proton plot are located in a region called the band of stability

11. Nuclear Stability and Decay
A nucleus may be unstable for several reasons:
Nucleus has too many neutrons relative to number of protons.
Decay occurs by turning a neutron into a proton and emitting a beta particle (electron) from the nucleus
Result: increase in p+ and decrease in n0

12. Nuclear Stability and Decay
Nucleus has too few neutrons relative to the number of protons.
Increase stability by converting a proton to a neutron by the nucleus capturing an electron

13. Nuclear Stability and Decay
Positron – a particle with the mass of an electron but with a positive charge. It may be emitted as a proton changes to a neutron

14. Nuclear Stability and Decay
All nuclei with atomic number 83 and higher are radioactive because they have too many n0 and p+ to be stable
Most emit alpha particles

15. Half-Life
Every radioisotope has a characteristic rate of decay measured by its half-life
Half-life – time required for one-half of the nuclei of a radioactive sample to decay to products

16. Transmutation Reactions
Transmutation – conversion of an atom of one element to an atom of another element.
Radioactive decay
Bombarding the nucleus with high-energy particles (p+, n0, or α)

17. Transmutation Reactions
The elements with atomic numbers greater than 92 are called the transuranium elements
None occur in nature, and all are radioactive
Synthesized in nuclear reactors

18. Nuclear Fission
When the nuclei of certain isotopes are bombarded with neutrons, they undergo fission, the splitting of a nucleus into smaller fragments
Fission reactions generate additional neutrons, which lead to a chain reaction

19. Nuclear Fusion
Fusion occurs when nuclei combine to produce a nucleus of greater mass
Requires very high temperatures to start the reaction.
At these temperatures, matter exists as plasma, a high-energy state in which ions exist in a gaslike form