Chemistry In Society #3: Nuclear Chemistry Flashcards
What does the stability of and atomic nucleus depend on?
The proton/neutron ration
What neutron:proton ratio is required for smaller elements?
1:1 for a stable nucleus
For larger (and heavier) atoms, what neutron:proton ratio is required?
1.5:1 for a stable nucleus
What is radioactive decay?
- the stability of an atomic nucleus depends on proton:neutron ratio
- radioactivity is the result of unstable nuclei rearranging to form stable nuclei with the emission of energy
Radiation is connected solely to… what does this mean?
- the nucleus
- it is independent of the physical state of the element and is not affected when the element for a compounds
How can the three types of radiation be studied?
Using an electric field
Alpha radiation
Slow moving positively charged particles attracted to the negative plate
Beta radiation
Fast moving negatively charged particles attracted to the positive plate
What is gamma radiation?
Electromagnetic radiation travelling at the speed of light. No deflection.
State the nature, symbol, charge, and mass of alpha particles
NATURE: He, nucleus
SYMBOL: ⁴ ₂He
CHARGE: 2+
MASS: 4
State the nature, symbol, charge, and mass of beta particles
NATURE: Electron
SYMBOL: ⁰ -₁e
CHARGE: 1-
MASS: 1/2000
State the nature, symbol, charge, and mass of gamma particles
NATURE: EMR
SYMBOL: None
CHARGE: None
MASS: None
What happens when a radioactive isotope decays by alpha emission?
The nucleus LOSES 2 protons and 2 NEUTRONS
*be sure to include the He isotope in the equation!
What happens in alpha radiation when the number of protons changes?
The element also changes.
This is TRANSMUTATION
BETA RADIATION SUMMARY (2)
- If a nucleus has to many neutrons, a neutron will be converted into a proton and an electron
- The proton stays inside the nucleus and the electron is ejected from the nucleus at beta radiation
(Product will have atomic number of one more than the reactant due to negative electron)
Gamma radiation summary (4)
- occurs within other types of radiation
- is a mechanism for releasing energy
- has no mass or charge
- does not affect the atomic or mass number
Why is it impossible to predict when a particular atom will decay?
The disintegration of a nucleus is an entirely random event
What IS radioactive decay predictable for?
A large population of unstable atoms (this predictability is called half life)
What is half life?
The time taken for half of the nuclei of a particular isotope to decay
Half lives summary (3)
- The disintegration of a nucleus is an envively random event and it is impossible to predict when a particular atom will decay.
- However, radioactive decay is predictable for a large population of unstable atoms.
- This predictability is called half life. It is the time taken for half of the nuclei of a particular isotope to decay.
Half life is abbreviated to
T1/2
What happens after ‘n’ half lives?
The fraction of the original activity which remains is (1/2)n
The half life of any isotope is independent of…
The mass, temperature, pressure, concentration, catalysts, or state of the sample
How are radioisotopes used in medicine?
The are used for radioactive labelling in the diagnosis and treatment of disease
How are radioisotopes used in industry?
241Am is used in smoke alarms
How are radioisotopes used in scientific research?
- 32P and 14C can be used to determine the uptake of phosphates and CO2 in plants
- this it called isotopic labelling
What is 14C?
A radioactive isotope formed in the upper atmosphere by the bombardment of nitrogen by neutrons
¹⁴ ₇N + ¹ ₀n —>
¹⁴ ₆C + ¹ ₁p
Half life of 14C
5600 years
Why is there a constant level of ¹⁴C in the air?
Because the rate of formation is equal to the rate of decay
Why do all plants and animals contain the radioisotope ¹⁴C?
¹⁴C is absorbed by plants during photosynthesis
Why will the radioactivity of the plant/animal decrease when it dies?
It no longer absorbs ¹⁴C
How can the age of a sample containing ¹⁴C be calculated?
Using t1/2 and comparing the activity of that with current ¹⁴C levels
