Quiz 3 Flashcards
stable atom
does not easily undergo spontaneous
change.
How does an unstable nucleus become more stable?
becomes more stable by the emission of radiation
followed by transition to a more stable state
nuclide
an atom with a specific atomic number and a specific mass number
radionuclide
a nuclide that is unstable and thus emits radiation
Correlations between nuclear stability and the number of nucleons in an atom
All nuclei with 84 or more protons present are unstable and all nucleons with a mass number greater than 209 are unstable.
Correlations between nuclear stability and the neutron to proton ratio in an atom
As the number of protons in successive atoms increases, so does the number of neutrons.
- For elements of low atomic number (20 or below), the neutron to proton ratio is very close to or
equal to one.
- For heavier elements (atomic number greater than 20), the neutron to proton ratio increase until
reaching a maximum of 1.5 (3 neutrons for every 2 protons).
more protons means
proton to proton repulsion will tend to make the nucleus less stable
more neutrons means
neutrons in the nucleus of an atom tends to increase the stability of the atom, up to
a certain point, because of the increased presence of the strong nuclear force
strong nuclear force
the powerful attractive force that binds protons and neutrons together in the nucleus
radioactivity
the radiation spontaneously emitted from an unstable nucleus
nuclides vs isotopes
nuclide- atom of an element with a specific atomic number and a specific mass number.
isotope- nuclides of the same element that have different numbers of neutrons and thus different mass numbers.
different notations for radioactive elements
1) element- atomic mass #
2) EAZ
radioactive decay
process whereby an unstable nucleus spontaneously emits radiation
radioactive nuclides
- do not all undergo radioactive decay at the same rate
- lower the radioactive decay rate the greater the stability of the radionuclide
half-life
- the time required for one half of any given quantity of a radioactive substance to undergo
ratioactive decay - constant
- (1/2) ^time/halflife
finding the fraction remaining
Copper - 67 has a half-life of 2.6 days. What fraction of atoms in a copper - 67 sample will remain in an undecayed state after…
- 5.2 days: 5.2/ 2.6 is 2, 1/2^2 is 1/4… 1/4 will remain
- Divide time over half life
- That (#) is the exponent over the (1/2)
- Answer is (1/2)^#
finding how many half-lives have elapsed
How many half-lives have elapsed if after 8.0 years the fraction of undecayed nuclides in a
particular sample of an element is…
1/16: 2^4 is 16, so that 4 is the number of half-lives
finding the undecayed amount
The half-life of copper - 60 is 2.4 minutes. How many grams of copper - 60 in an 8.0 gram sample
will remain undecayed after the following periods of time?
4.8 minutes: 2 half lives elapsed, (1/2)^2 is 1/4*8 (grams) is 2 grams remaining or undecayed
finding the decayed amount
The half-life of copper - 60 is 2.4 minutes. How many grams of copper - 60 in an 8.0 gram sample
will remain undecayed after the following periods of time?
4.8 minutes: 2 half lives elapsed, (1/2)^2 is 1/4*8 (grams) is 2 grams. 8-2 is 6 grams decayed.
finding how long it takes for decay
Iron - 52 has a half-life of 8.0 hours. How long will it take, in hours, for the following fractions of
nuclides in an iron - 52 sample to decay?
3/4: the denominator is 4, and (1/2)^2 is 1/4, so 2 half-lives have passed, meaning 8*2 is 16 hours
alpha particle
mass: 4 amu
charge: 2+
2 protons 2 neutrons
beta particle
mass: .0005 amu
charge: 1-
gamma particle
mass: 0
charge: 0
What physical manifestation indicates that an atom possesses an unstable nucleus?
nucleus can undergo spontaneous change, leading to emission of radioactivity
How do the neutron to proton ratios compare for stable nuclei of low atomic number and stable
nuclei of high atomic number?
For atoms of lower atomic number (Z = 20 and below), the neutron to proton ratio is approximately
1 to 1
As the atomic number increases beyond approximately 20, the neutron to proton ratio of stable
nuclides increases as well until it reaches a maximum of 3 to 2; that is, for every 2 protons in the
nucleus of such atoms there are three neutrons as well.
How did Henri Becquerel discover radioactivity?
He noticed that minerals containing uranium
emitted a penetrating radiation that caused photographic plates to be exposed even though the
minerals had not been previously exposed to light – a requirement to produce phosphorescence.
He also found that the radiation emitted created an electrical discharge in air and that the intensity
of this discharge was related to the intensity of the radiation.
What did Marie Curie and Pierre Curie learn during their studies of radiation?
intensity of the radiation emitted is proportional to the
concentration of the radioactive element within it and not the formula of the mineral or compound.
intensity of the radiation emitted from a sample was unaffected by
temperature, pressure, or other physical or chemical conditions.
What did Ernest Rutherford and Frederick Soddy find about radioactive decay that was met with
disbelief by others in the scientific community?
radioactive emission could result in the change of one
element into another
