Nuclear Chemistry

1
Nuclear Chemistry

• Some Notes and Thawts

2
A Comparison Between Chemical and Nuclear
Reactions.
3
Where the Action Is

• In chemical reactions, the electrons do the work
  while the nucleus is idol.

• In nuclear reactions, the nucleus is changed
  while the orbital electrons are bystanders.

4
What Is Changed?

• In chemical rxns, substances are changed, but
  atoms never change identity.

• In nuclear rxns, atoms of an element change to
  atoms of another element.

5
What About Energy and Mass?

• In chemical rxns, there are small changes in
  energy and no measurable changes in mass.

• In nuclear rxns, there are large changes in
  energy and often large changes in mass.

6
What Affects the Reactions?

• Chemical rxns are affected by temperature,
  concentration, nature of substances and catalysis.

• Nuclear rxns are only affected by number of
  nuclei.

7
Definitions
8
Radioactivity

• The spontaneous disintegration or decay of an
  unstable nucleus by means of emission of
  radiation.

9
Nuclide

• An atom with a particular nuclear composition,
  that is, a certain number of two types of
  nucleonsprotons and neutrons. A nuclide is a
  particular isotope.

10
The Nucleus

• The center of the atom.
• 1/10,000 of the diameter.
• One trillionth of its volume.
• Incredibly dense 1014 g/ml.

11
A Brief History
12
Henri Becquerel

• Discover that Uranium minerals emit radiation
  that make bright images on photographic plates.

13
Marie Curie

• Discovered intensity of radiation is proportional
  to concentration of element.
• Isolated radioactive components and found new
  elements,
• Isolated radium.

14
Rutherford and Soddy

• Proposed that when a nuclide decays, it becomes
  the nuclide of another elementthis was
  outrageous at the time.

15
The Three Common Types of Radioactive Emission
16
Alpha Particles

• These are large particles Helium Nuclei.

17
Beta Particles

• Negatively charged.
• Fast electrons.

18
Gamma Rays

• Very high energy photons.
• Pure energy.
• From the excited nucleus.

19
Types of Radioactive Decay
20
Alpha (a) Decay

• Involves the loss of an alpha particle from the
  nucleus.
• A decreases by 4 and Z decreases by 2.

21
Beta (b) Decay

• Involves the ejection of a b particle from the
  nucleus.
• A stream of electrons.
• Next higher element is formed.

22
How Do Electrons Emit From the Nucleus?

• A neutron is converted into a proton and a beta
  particle which is ejected/

23
Positron Decay

• Emission of positron from the nucleus.
• Antiparticle of an electron

24
Where Does It Come From?

• Proton is converted to a neutron and a positron.
• Next lower element is formed

25
Electron Capture

• Nucleus of atom draws in a surrounding electron
• From low energy level

26
What Actually happens?

• Proton in the nucleus combines with electron to
  form a neutron.

27
Gamma Emission

• Pure radiation of high energy photons from an
  excited nucleus.
• Usually in ultraviolet or infrared light
• Gamma emissions accompany most types of decay.

28
Nuclear Stability

• N/Z Ratio

29
Neutron to Proton Ratio

• As atoms get larger, N/Z ratio increases as
  neutrons increase to stabilize the strong force.
• Competition between strong force and repulsive
  force determines stability.

30

• Atoms with even Z have more stable nuclides.
• Nucleon pairing is similar to electron pairing.
• Unstable nuclei change N/Z to attain stability.

31
What Are the Rules?

• Few nuclides exist for N/Zlt1
• No stable nuclides for N/Z1 for Zgt20.
• All nuclides above Z83 are unstable.

32
Son of Rules

• Neutron rich nuclides hi N/Z undergo beta
  decay.
• Proton rich nuclides lo N/Z undergo positron
  decay or electron capture.
• Heavy nuclides Zgt83 undergo alpha decay.