J. Nuclear Chemistry Flashcards
(59 cards)
Energy is _____ when light nuclei fuse together to give elements of higher atomic number
(e.g., carbon-12 + alpha particle → oxygen-16 + gamma radiation)
released
strong force vs electromagnetic force
strong force - short attractive forces that binds nucleons (protons + nucleus)
electromagnetic force - long-range relatively weak force between electric charges to bound electrons to nuclei to form atoms
Nuclear reactions are very much more energetic than normal chemical reactions because ______
strong force is much stronger than the electromagnetic force that binds electrons to nuclei
Elements up to Z=26 is formed inside ___ and products of nuclear fusion rxns called _____
inside the stars → nuclear burning
What is a neutrino?
v (nu) - electrically neutral and very small (~0) mass released during nuclear reactions usually accompanied by released of positron (e+)
Moderately energetic collisions (low to moderate temperature) between species can result in ____, but only highly vigorous collisions (extreme temperatures) can provide the energy required to _____.
Moderate temp = chemical change
Extreme temp = (can make) nuclear reactions
Represents the difference in energy between the nucleus itself and the same numbers of individual protons and neutrons.
Binding energy = (Δm)c^2
Δm = m nucleons - m nucleus
A positive binding energy corresponds to a nucleus that ____ than its constituent nucleons
has a lower, more favorable, energy (and lower mass)
a large binding energy signifies a ____
stable nucleus
total mass number and overall charge are ____ in nuclear reactions
conserved → balanced on each side of rxn
Heavier nuclides are formed by processes that include ____ and subsequent ___
neutron capture and subsequent beta decay
Differentiate isotopes, isobar, isotone
- Isotopes - same elements (same proton/atomic number), same chemical properties), different mass number (different neutrons
- Isobar - different element (different proton, atomic number), different neutrons BUT equal mass number and same physical property
Sn-124, Te-124, Xe-124 - Isotone - different element (different proton, atomic number), different mass number BUT equal no. of neutrons
Differentiate nuclides vs nucleons
Nuclides - specific type of nucleus defined by Z and A
Nucleons - particles in the nucleus (protons and neutrons), together = mass of nucleus
Nuclear stability depends on ___ and ____
- number of nucleons
- neutron-to-proton ratio (n/p)
For a stable nuclide, its n/p ratio is equal to ____
n/p ratio = 1
→ explains why smaller nuclides have equal number of neutrons and protons
Why heavier (Z>84) nuclides are more unstable than smaller nuclides?
As atomic number increases, the atom need more neutrons to neutralize the charge of proton (lessen the repulsion) and bind particles together
Typical characteristics for a stable nuclide (3)
- Z<20 (n/p=1)
- even numbers of proton and neutrons
- contain magic numbers of protons or neutrons (2, 8, 20, 50, 82, 126)
What are the magic numbers and what do they imply?
2, 8, 20, 50, 82, 126 protons or neutrons
→ stable nuclides
Typical characteristics for unstable nuclide (3)
- Z>83
- odd numbers of protons and neutrons
- n/p > 1
How to predict if unstable nuclide will undergo alpha decay?
Z>83
How to predict if unstable nuclide will undergo beta decay?
Z = 1-20 → n/p > 1.00
Z = 21-40 → n/p > 1.25
Z = 41-82 → n/p >1 .50
How to predict if unstable nuclide will undergo positron emission or electron capture?
POSITRON EMISSION
Z = 1-20 → n/p < 1.00
Z = 21-40 → n/p < 1.25
ELECTRON CAPTURE
Z = 41-82 → n/p < 1.50
Energy change that drives nuclear reactions (separate nucleus into its protons and neutrons)
nuclear binding energy
E= Δm c^2
Δm = total mass of indv. particles - actual mass of atom
The mass of separated nucleons is ____ the mass of nucleus
greater
→ some of the mass in nucleus is converted to binding energy
