Quiz 3

Question 1

stable atom

Answer 1

does not easily undergo spontaneous

change.

Question 2

How does an unstable nucleus become more stable?

Answer 2

becomes more stable by the emission of radiation

followed by transition to a more stable state

Question 3

nuclide

Answer 3

an atom with a specific atomic number and a specific mass number

Question 4

radionuclide

Answer 4

a nuclide that is unstable and thus emits radiation

Question 5

Correlations between nuclear stability and the number of nucleons in an atom

Answer 5

All nuclei with 84 or more protons present are unstable and all nucleons with a mass number greater than 209 are unstable.

Question 6

Correlations between nuclear stability and the neutron to proton ratio in an atom

Answer 6

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).

Question 7

more protons means

Answer 7

proton to proton repulsion will tend to make the nucleus less stable

Question 8

more neutrons means

Answer 8

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

Question 9

strong nuclear force

Answer 9

the powerful attractive force that binds protons and neutrons together in the nucleus

Question 10

radioactivity

Answer 10

the radiation spontaneously emitted from an unstable nucleus

Question 11

nuclides vs isotopes

Answer 11

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.

Question 12

different notations for radioactive elements

Answer 12

1) element- atomic mass #

2) EAZ

Question 13

radioactive decay

Answer 13

process whereby an unstable nucleus spontaneously emits radiation

Question 14

radioactive nuclides

Answer 14

• do not all undergo radioactive decay at the same rate

- lower the radioactive decay rate the greater the stability of the radionuclide

Question 15

half-life

Answer 15

• the time required for one half of any given quantity of a radioactive substance to undergo
  ratioactive decay
• constant
• (1/2) ^time/halflife

Question 16

finding the fraction remaining

Answer 16

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)^#

Question 17

finding how many half-lives have elapsed

Answer 17

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

Question 18

finding the undecayed amount

Answer 18

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

Question 19

finding the decayed amount

Answer 19

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.

Question 20

finding how long it takes for decay

Answer 20

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

Question 21

alpha particle

Answer 21

mass: 4 amu
charge: 2+
2 protons 2 neutrons

Question 22

beta particle

Answer 22

mass: .0005 amu
charge: 1-

Question 23

gamma particle

Answer 23

mass: 0
charge: 0

Question 24

What physical manifestation indicates that an atom possesses an unstable nucleus?

Answer 24

nucleus can undergo spontaneous change, leading to emission of radioactivity

Question 25

How do the neutron to proton ratios compare for stable nuclei of low atomic number and stable
nuclei of high atomic number?

Answer 25

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.

Question 26

How did Henri Becquerel discover radioactivity?

Answer 26

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.

Question 27

What did Marie Curie and Pierre Curie learn during their studies of radiation?

Answer 27

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.

Question 28

What did Ernest Rutherford and Frederick Soddy find about radioactive decay that was met with
disbelief by others in the scientific community?

Answer 28

radioactive emission could result in the change of one

element into another