Topic 1: Nuclear Chemistry Flashcards
What is a positron?
Positron is a positive electron that is not present in stable atoms.
Define atomic number and mass number
- Atomic number: number of protons
- Mass number: total number of nucleons
What feature of an atom does atomic number define?
The chemical nature of the atom
What is a nuclide?
An atom with particular mass number and atomic number
What are isotopes?
Nuclides with same atomic number but different mass number
How is atomic mass calculated?
Average of atomic masses and abundances of each of the naturally-occuring isotopes
What is nucleogenesis?
Formation of nuclei from existing nucleons
How are atoms of elements generated (from what element and via what reaction)?
Generated from hydrogen, simplest nuclei, by nuclear reactions
Describe properties of hydrogen burning reaction, where does it happen and how it is different from Fe
As hydrogen fuses, it releases heat and radition into the surrounding environment.
When hydrogen is exhausted, helium starts to burn and it keeps going up the periodic table until Fe.
All elements up to Fe are produced in stars. When iron being burned, it consumes energy and implodes, forming a supernova.
Classify 2 types of atomic nuclei and how they turn from one to another
Radioactive and stable
Radioactive nuclei undergoes spontaneous decay to become a stable nuclei
Name 2 characteristic features unique to each radioactive nuclei
- Mode of decay
- Half life
What is half-life?
The time required for half of the nuclei in a sample to undergo a decay event
State the formula for the exponential decay curve
N = N(0)e^(-kt)
Explain the difference between decay constant and rate of decay
- Decay constant (k) does not depend on the size of sample
- Rate of decay depends on the size of sample
What is activity of a radioactive sample and what is its unit?
Activity is a specific measurement of rate of decay, defined as the number of nuclei that disintegrate per second.
1 Becquerel = 1 disintegration per second (s^-1)
Describe the relationship between activity and number of nuclei in the sample with a formula
A = kN
Identify and describe 2 types of activity of radioactive nuclei
- Specific activity: activity per gram of radioactive nuclei
- Molar activity: activity per mole of radioactive nuclei
Describe the relationship between activity, decay constant, and half-life
- Low activity = small decay constant = long half-life
- High activity = large decay constant = short half-life
Describe a gamma ray
Has energy, but no mass or charge
Why is there a positron as a product when 2 hydrogen nuclei react with each other?
When 2 hydrogen nuclei react, they give a hydrogen atom which means 1 proton has to give off its positive charge to become a neutral neutron. That positive charge is positron.
Write the hydrogen fusion equation
4 (1-1)H –> (4-2)He + 2 (0-1)e + 2y
C-14 dating is appropriate for objects dating back to how many years?
Less than 60,000 years old
