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Bettel Plus Chang Chemistry > Nuclear (Chang) > Flashcards

Nuclear (Chang) Flashcards

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1
Q

Radioactivity

A

Unstable nuclei emitting particles/ electromagnetic radiation spontaneously

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2
Q

Radioactive elements

A

Atomic number greater than 83

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3
Q

Nuclear transmutation

A

Results from bombardment of nuclei by neutrons, protons, or other nuclei

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4
Q

Nuclear reactions

A

-radioactive decay and nuclear transmutation

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5
Q

(A) Chemical reactions
(B) Nuclear reactions

A
  1. (A) atoms are rearranged by the breaking and forming of chemical bonds
    (B) Elements (or isotopes of the same elements) are converted from one to another

2.
(A) Only electrons in atomic orbitals are involved in the breaking and forming of bonds
(B) Protons, neutrons, electrons, and other elementary particles may be involved

  1. (A) Reactions are accompanied by absorption or release of relatively small amounts of energy
    (B) Reactions are accompanied by absorption or release of tremendous amounts of energy
  2. (A) Rates of reaction are influenced by temperature, pressure, concentration, and catalysts
    (B) Rates of reaction normally are not affected by temperature, pressure, and catalysts
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6
Q

Nuclear stability

A

-nucleus: densest portion of atom (most mass, least volume)
-Coulomb’s law: like charges repel. But there are also SHORT RANGE ATTRACTIONS between prot-prot, prot-neut
-stability depends on the difference between coulombic repulsion and short range attraction

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7
Q

Neutron-to-proton ratio

A

-principal factor in nuclear stability
-low atomic number elements: n/p is close to 1
-⬆️ atomic number, n/p becomes greater than 1
-larger number of neutrons are needed to counteract strong repulsion among protons

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8
Q

Predicting nuclear stability

A

-Nuclei more stable if either proton/ neutron are:
2, 8, 20, 28, 50, 82, 126 (magic numbers)
-Nuclei with EVEN numbers of BOTH protons and neutrons are MORE STABLE than with ofd numbers
-Isotopes of elements with atomic number higher than 83 are radioactive: including Technetium (Z=43) and Promethium (Z=61)

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9
Q

Belt of stability

A

-# Neutrons vs # Protons
-stable nuclei

•above belt, nuclei with higher n/p ratio
-to lower ratio (move toward belt), undergo beta-particle emission (increase of proton, decrease neutron)

•below belt, nuclei with lower n/p ratio
-to increase ratio, undergo positron emission or electron capture

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10
Q

Nuclear binding energy

A

-quantitative measure of nuclear stability
-energy required to break up nucleus into its components protons and neutrons
-conversion of mass to energy that occurs during EXOTHERMIC NUCLEAR REACTION

∆E=∆mc^2
Energy/mass of product - energy/mass of reactant

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11
Q

Mass defect

A

-Difference between mass of an atom and the sum of the masses of its protons, neutrons and electrons

-masses of nuclei are always less than sum of the masses of nucleons (protons and neutrons)

-loss in mass is converted as energy released (negative energy)

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12
Q

Nuclear binding energy per nucleon

A

= nuclear binding energy (J)/ number of nucleons, protons+neutrons (nucleons)

-highest binding energies per nucleon: mass number 40-100 (esp. iron, cobalt, nickel region); highest attraction of protons and neutrins

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13
Q

Radioactive decay series

A

Sequence of nuclear reactions that ultimately result in the formation of stable isotope

•Parent: beginning radioactive isotope
•Daughter: profuct

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14
Q

Kinetics of radioactive decay

A

All radioactive decays obey FIRST ORDER KINETICS
-rate constants are unaffected by changes in environment (temp and pressure)

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15
Q

Radiocarbon dating (Uranium-238 Isotopes)

A

-estimating age of rocks in earth and extraterrestrial objects
-half-life of first step: U(238,92) ➡️ Th(234,90): 4.51x10^9 years (rate determining step; assume as half life for the overall process U(238,92) ➡️ Pb(206,82)

-estimate age of rocks from mass ratio of Pb(206,82) and U(238,92)
-if half mole of U(238,92) decayed, mass ratio=0.866
-higher ratio: rock exists longer than 4.51x10^-9 vice versa

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16
Q

Earth

A

4.5 x 10^9 years old
4.5 billion

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17
Q

Dating using Potassium-40 Isotopes

A

-important in geochemistry
-electron capture
K(40,19) + e(0,-1) ➡️ Ar(40,18)
Half life: 1.2 x 10^9 years

-gaseous argon trapped in mineral latice; escape only if material is melted
-amount of ar-49 present: mass spectrometer
-Dating: ratio of argon-40 to potassium-40

18
Q

Nuclear transmutation

A

-producing radioactivity artificially
-collision of two particles
-Rutherford (1919): 14,7,N(a,p)17,8O
•first time: feasibility of converting one element to another

19
Q

Synthetic isotopes

A

-prepared using neutrons as projectiles
(i.e. Lithium and neutron: tritium)

20
Q

Particle accelerator

A

-uses electric and magnetic fields to increase the kinetic energy of charged species so that reaction will occur
-linear path: 3 km- particle with speed of above 90% of the speed of light

21
Q

Transuranium elements

A

-elements with atomic number greater than 92
-synthesize using particle accelerator

22
Q

Nuclear fission

A

-heavy nucleus (mass number > 200) divides to form smaller nuclei of intermediate mass and one or more neutrons
-releases large amount of energy (heavy nucleus: more unstable ➡️ smaller nuclei: less unstable)

-first nuclear fission: U-235 bombarded with slow neutrons
Representative rxn:
235,92U + 1,0n ➡️ 90,38 Sr + 143,54 Xe + 3 1,0n

23
Q

Nuclear chain reaction

A

Uranium-235 fission
-more neutrons produced than originally captured
-self-sustaining sequence of nuclear fission reactions

•Subcritical mass: no chain reaction since small amount of Uranium only
•Critical mass: minimum mass of fissionable material required to generate a self-sustaining nuclear chain reaction

24
Q

Atomic bomb

A

-first application of nuclear fission
-tons of Trinitrotoluene (TNT) explosive and subcritical U-235 wedge

-U235: Hiroshima, Japan, 1945
-Pt239: Nagasaki, Japan

25
Q

Nuclear reactors

A

-application nuclear fission
-generation of electricity using heat from controlled chain reaction

26
Q

Light water reactor

A

-slow neutrons split U-235 more efficiently; neutrons produced move at high velocity
•Moderators: substances that reduce kinetic energy of neutrons; nontoxic, inexpensive, resist conversion into radioactive substance by neutron bombardment (light water, 1,1H)
-nuclear fuel: Uranium oxide U3O8
-factor limiting rate of reaction: number of neutrons present (controlled by lowering cadmium/ boron rods; captures neutrons)
-cooling system: absorb heat released and transfer it outside reactor core; produce enough steam to drive electric generator)

27
Q

Heavy water reactor

A

-Uses D2O rather than H2O
-deuterium absorption of neutrons: less efficient; reactor more efficient, doesn’t require enriched uranium
-eliminates the need for expensive uranium enrichment facilities
-D2O prepared by fractional distillation/ electrolysis of ordinary water (expensive)
-used by Canada: abundant hydroelectric power

28
Q

Breeder reactor

A

-produces more fissionable materials than it uses
-nuclear fuel containing U235 or Pu239 is mixed with U238. For every U235/P239 undergoing fission, more than one neutron is captured by U238 to generate Pu239
-7 to 10 years to regenerate sizable amount of material needed to refuel original reactor and to fuel another reactor of comparable size (doubling time)

29
Q

Three Mile Island reactor accident (1979)

A

-Pennsylvania
-very little radiation escaped the reactor

30
Q

Chernobyl nuclear accident (1986)

A

-in Belarus
-fire and explosion followed by released of radioactive material

31
Q

Nuclear fusion

A

-combining of small nuclei into larger ones
-two light nuclei combine together, forms larger and more stable nuclei, energy released
-constantly occurs in the sun (H and He)
-THERMONUCLEAR REACTIONS: only take place at very high temperature
-state of matter at very high temp (100 million degrees C):
PLASMA- gaseous mixture of positive ions and electrons

32
Q

Hydrogen bomb

A

-application of nuclear fusion and fission
-aka thermonuclear bomb
-contain solid lithium deuteride (LiD)
-detonation: two stages
•FISSION: required temp for fusion achieved with atomic bomb
•FUSION: releasing vast amount of energy
Li+D ➡️ 2alpha
D+D ➡️ T+H

-cleaner than atomic bomb since tritium (weak beta particle emitter) is the only radioactive isotope produced

33
Q

Uses of isotopes
1. Structural determination

A

-structure of thiosulfate ion (S2O3^2-)
[S center, bonded to O O O S, imbes na linear O S O S O]
-rafioactive sulfur-35 isotope acts as label for “S” atoms
SO3,2- + S ➡️ S2O3,2-
S2O3,2- ➡️ SO3,2- + S

34
Q

Uses of isotopes
2. Study of photosynthesis

A

-radioactive C14 isotope: determine the path of carbon in photosynthesis
-TRACES: isotopes, especially radioactive isotopes that are used to trace the path of atoms of an element in a chemical or biological process;
Can be detected by photographic techniques or Geiger counter

35
Q

Uses of isotopes
3. Isotopes in medicine

A

-tracers: used in diagnosis
-Na24 injected into bloodstream; monitored to trace flow of blood and detect obstruction
-I131 activity of thyroid gland; measure radioactivity just above thyroid gland to see if iodine is absorbed at normal rate
-Tc99; first artificially prepared element; patients drink/ injected solution containing Tc99- images of organs

36
Q

Quantitative measures of radiation

A

•fundamental unit of radioactivity: Curie, Ci
1 Ci = 3.7x10^10 nuclear disintegrations/ sec
Decay rate equivalent to 1g of Radium

•Intensity of radiation
Radiation absorbed dose (rad): amount of radiation that results in the absorption of 1x10^-5 J per gram of irradiated material.

Roentgen equivalent for man (rem)
1 rem = 1 rad x 1 RBE (Relative biological effectiveness)

*Biological effect of radiation depends on body part irradiated and type of radiation

37
Q

Biological effects of types of nuclear radiation

A

MOST PENETRATING
Gamma (cannot be stopped by shielding materials since no charge)
Beta
Alpha (when ingested, damaging effects are greatly aggravated)
LEAST PENETRATING

38
Q

Radicals (free radicals)

A

-Molecular fragments having one or more unpaired electrons
-short lived and highly reactive

39
Q

Radiation damage

A

•Somatic
-injuries that affect organism during its lifetime (sunburn, skin rash, cancer)

•Genetic
-inheritable changes or gene mutations (deformed offspring)

40
Q

Food irradiation

A

-food exposed to levels of radiation to kill insects and harmful bacteria
-packaged airtight containers; stored for months without deterioration

Bettel Plus Chang Chemistry (19 decks)

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