Nuclear Chemistry Worksheet Answer Key Flashcard

Nuclide
Nucleus of a specific isotope.
Nuclear Reaction
1. The reaction does not depend on the chemical environment.
2. E change is much greater than E change during a chemical reaction.
3. Factors such as T, P, or catalyst don’t affect rate.
4. Nucleus of the atom changes, usually producing a different element.
5. They are different of different isotopes, while isotopes of same element have no affect on chemical reactions.
Nucleons
A collection of protons and neutrons, or just a proton or a neutron.
Radioactive nucleus
An unstable atomic nucleus that by spontaneous disintegration emits radiation.
Alpha Radiation
1. Repelled by positively charged electrode.
2. Attracted by negatively charged electrode.
3. Has a 2+ charge and atomic mass of 4 (2 protons, 2 neutrons), consistent with identity of Helium.
4. Written as Helium in nuclear equations.
Change in Atomic Number: -2
Change in Mass Number: -4
Change in Neutron Number: -2
Beta Emission
Beta Emission
Occurs when a neutron in the nucleus decays into a proton and an electron. The proton stays in the nucleus, but the electron is ejected.
Change in Atomic Number: +1
Change in Mass Number: 0
Change in Neutron Number: -1
Positron Emission
Occurs when a proton in the nucleus decays into a neutron and a positron (a positive electron). The neutron stays in the nucleus, but the positron is ejected.
Change in Atomic Number: -1
Change in Mass Number: 0
Change in Neutron Number: +1
Gamma Radiation
Consists not of particles (like alpha and beta), but of high energy photons. It’s almost always observed together with alpha and beta radiation.
Change in Atomic Number: 0
Change in Mass Number: 0
Change in Neutron Number: 0
Radioactive Decay
First order process.
Decay rate =λ x N
λ= decay constant N=number of radioactive nuclei
Integrated rate law: ln(N/N_0)=-λt
N_0=number radioactive nuclei initially present
N=number remaining at time t
λ=decay constant in units 1/time
Half-life t1/2
Time required for number of radioactive nuclei in a sample to drop to half the initial value; does not depend in size of sample, temperature, or any other external condition (unlike chemical reactions).
Fraction of nuclei remaining after “n” half life times
N_n/N_0=(1/2)^n
Nuclear Stability
Nuclei with up to 20 protons are stable when neutrons and protons have close 1:1 ratio.
Nuclei of 20<Z more neutrons are needed for stability of the nucleus if nucleus has more protons.
Band of Stability
Any nuclei with Z> 83 is radioactive.
Too many neutrons (above zone of stability)=beta emission.
Too many protons (below zone of stability)= positron emission.
Stable Isotopes
Radioactive, half-lives can be measured.
Unstable Isotopes
Radioactive, decay too rapidly for half-lives to be observed.
Nonradioactive/Stable
Do not undergo radioactive decay.
Energy released during nuclear reactions
Happens when a nucleus forms from its free and isolated protons; as more is released, resulting nucleus is more stable and forces holding nucleons together is stronger.
Mass Defect
Loss in mass that occurs when isolated protons and neutrons combine to form a nucleus.
Binding Energy
The mass defect converted into energy that is released during the nuclear reaction; direct measure of the forces holding the nucleons together (stability of the nucleus).
It means that this much E is released when free protons and neutrons form a new nucleus, or this much E is needed to disintegrate a nucleus into isolated protons and neutrons.
Larger value=more stability.
Nuclear fission
The process of very heavy elements gaining stability and releasing E if they fragment to yield midweight elements (more stable); splitting of a large nucleus into smaller ones.
Nuclear fusion
The process of very light elements gaining stability and releasing E if they fuse together; the joining together of light nuclei.
Nuclear chain reaction
Nuclear chain reaction
A self-sustained series of nuclear fission reactions; can be sustained only when a minimum mass of a fissile isotope is present.
Subcritical fission proccess
On average, less than on neutron causes another fission event, and the reaction dies out (think downward slope).
Critical fission process
One neutron from each fission event causes another fission event. The process sustains itself at the same level (think upward slope).
Supercritical fission process
More than one neutron from each fission event causes another fission event. The process escalates rapidly, and the heat buildup causes a violent explosion (think exponential slope).
Critical Mass
A certain mass of fissionable material (protons and neutrons) needed to achieve the critical state.

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