Atomic structure Flashcards
Z
atomic number (number of protons in the atom)
letter designated for atomic number
Z
What does atomic number represent?
number of protons in the atom
A
mass number (protons + neutrons)
atoms with same Z, but different A:
Isotope, same number of protons but different number of neutrons (different number of neutrons)
How many electrons are in the inner shell?
2
What is the K-shell
inner most electron shell holding two electrons
K, L, M number of electrons
2, 8, 18
What is the “binding force”?
attractive forces between negatively charged electrons and positively charged protons.
What electron shell has the highest binding force?
K-shell. strength of the binding force is inversely proportional to the square of the distance between the nucleus and the electrons
What is the mass defect of the nucleus?
Difference in the mass of the individual nucleons measured separately compared to their mass when bound in the nucleus When nucleons are bound together within the nucleus by the nuclear force, the total mass of the nucleus is less than the mass of the individual nucleons when considered separately. The difference is the binding energy of the nucleus.
When nucleons are bound together within the nucleus by the nuclear force, the total mass of the nucleus is _____ than the mass of the individual nucleons when considered separately.
When nucleons are bound together within the nucleus by the nuclear force, the total mass of the nucleus is LESS than the mass of the individual nucleons when considered separately.
The graph shows an estimated x-ray spectrum for a molybdenum anode x-ray tube. What do the “spikes” represent?
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The energy emitted by a outer shell electron that has filled a K-shell vacancy (characteristic radiation).
During the production of x-rays within an x-ray tube, the accelerated electrons can strike an electron of the target directly and eject the electron. The vacancy is filled by electrons from an outer electron shell. The energy differences between the outer and inner shell is emitted as a photon. The “spike” observed on the graph is associated with the distinct energy difference of the electron energy levels that have filled the inner-shell vacancy. For diagnostic x-ray tubes only ejection of k-shell electrons is relevant, as these photons have high enough energy not to be filtered by the tube envelope and additional filtration.
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binding energy of any nuclide can be calculated by:
The binding energy can be calculated by subtracting the atomic weight from the sum of the weight of the individual nucleons and electrons.
The total binding energy of an atom is the total amount of energy required to hold the individual particles together, or, conversely, is the amount of energy required to break the atom apart.
electron binding energy is defined by
the amount of energy required to ionize an atom
An inner shell vacancy is filled with an electron with simultaneous release of an electron from the same atom, resulting in 2 vacancies
An Auger electron is an electron that is emitted, rather than a photon, when lower level vacancies are filled. Auger electrons can be emitted from any atom. When an L-shell electron fills a K-shell vacancy, another L-shell electron can be emitted rather than a photon. The Auger electron carries off the extra energy rather than a photon, as would otherwise be expected. The emission of an Auger electron leaves 2 vacancies. In heavier atoms, cascades of photons can occur as these vacancies are filled.
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In order to maintain nuclear stability in large nuclei, what happens to A?
A increases (A= protons +neutrons). Specifically, neutrons increase
In order to offset the coulomb repulsion of the protons as the nuclei get heavier, additional neutrons are needed in the nucleus. Because the neutron does not have a charge but is still affected by the nuclear force, the total binding energy per nucleon increases within the nucleus. This increase also increases the stability of the atom. Thus, as the nucleus increases, a higher neutron-to-proton ratio is necessary.
Photons with wavelengths in the electromagnetic regions that can cause ionization events do so because?
Absorbed energy in the atom exceeds the electron binding energy
How does an electron lose energy in matter?
Electrons lose energy as they move through matter due to both collisional and radiative losses.
The electrons may collide with other particles or may lose energy due to other interactions within the electromagnetic field of the atom. An approximation of the ration of radiative energy losses to collisional energy losses is approximately (ZE/800), where E is the electron energy in MeV and Z is the atomic number of the target nuclide.
indirect measure of photon energy or the hardness of a beam
isobar
alpha particle
alpha particle = Helium nucleus without electrons
2 protons, 2 neutrons
2+ charge
Alpha particles are very heavy and contain high amounts of energy (4-10 MeV). Their speed is ~20000km/s and they interact with matter, causing much ionization over a very short distance.
What is alpha decay?
an alpha particle (containing two neutrons and two protons) is ejected from the nucleus. An alpha particle is identical to the nucleus of a helium atom.
All nuclei with the atomic number (Z) greater than 82, are considered unstable. These are considered “neutron-rich” and undergo alpha decay commonly.
Alpha particles are very heavy and contain high amounts of energy (4-10 MeV). Their speed is ~20000km/s and they interact with matter, causing much ionization over a very short distance.
What is the Z and A for an alpha particle, and how is this typically represented for elements undergoing alpha decay?
there are 2 protons and 2 neutrons in an alpha particle (aka, a helium nucleus)
A (mass number: protons + neutrons) = 4
Z (atomic number: protons only) = 2
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Is the number of electrons in a neutral atom denoted by A or Z?
Z!
Z = atomic number (number of protons)
To have a neutral atom, protons = electrons. Therefore # of electrons in a neutral atom = Z
Isotone
Isotone: are atomic species that share the same number of neutrons, and differ in the number of protons.
Same Z (number of Protons) = isotoPes
Same A (number of nucleons) = isobArs
Same N (number of Neutrons) = isotoNes
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IsotoPes: same Z (same # of protons), different A (mass number, aka different # of neutrons)
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IsobAr: same A (mass number), different Z
aka, different elements with the same mass number
Which is more pentrating: charged particulate radiation or photons?
photons are more penetrating than charged particulate radiation
types of isobaric transitions
beta decay and positron decay isobAric means the Atomic number is the same. Z changes.
when an unstable atomic nucleus decays by converting a neutron into a proton with the emission of an anti-neutrino:
beta minus decay
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type of decay
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beta minus
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when does beta decay occur?
when nuclei have an ustable, excess number of neutrons relative to the number of protons.
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What nuclear decay occurs to the left of the blue line?
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beta minus decay.
too many neutrons –> beta minus decay
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what type of nuclear decay happens towards the top of the band of stability?
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alpha decay
too many protons and neutrons
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what type of nuclear decay happens to the right of the red line?
beta plus emission
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Z of _____ are structurally stable (and therefore not radioactive)
20