Ms. Sipe. Nuclear Chemistry Reactions in the nuclei of atoms Nuclear reactions Changes in the nuclei...
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Transcript of Ms. Sipe. Nuclear Chemistry Reactions in the nuclei of atoms Nuclear reactions Changes in the nuclei...
Ms. Sipe
Nuclear ChemistryReactions in the nuclei of atomsNuclear reactionsChanges in the nucleiInvolve the emission of energy- rays or
particlesNot affected by temperature, pressure , or
catalysts like regular chemical reactions
In chemical rxns bonds break and rearrange to form new substance (reactivity based on what subatomic particle?)
Nuclear ChemistryTypes of nuclear reactions
Fusion- combining of nuclei, releases a lot of energyStars and the sun
Fission- splitting of nuclei into smaller nucleiRadioactive Decay or radioactivityReactions begin with unstable isotopes called
radioisotopes that undergo change to become stable
Nuclear FusionThe energy emitted by the sun results from nuclear fusion.
• Fusion occurs when nuclei combine to produce a nucleus of greater mass.
• In solar fusion, hydrogen nuclei (protons) fuse to make helium nuclei. A LOT OF ENERGY PRODUCED!
The reaction also produces two positrons.
Nuclear FissionThe figure below shows how uranium-235 breaks into two smaller fragments of roughly the same size when struck by a slow-moving neutron.
More neutrons are released by the fission.
These neutrons strike the nuclei of other uranium-235 atoms, which cause chain reactions.
UUranium-235(fissionable)
23592 U
Uranium-236(very unstable)
23692
BaBarium-142
14256
KrKrypton-91
9136
3 n10
Neutron
Recap: Fusion vs Fission
Combining 2 light nuclei to form a heavier nucleus
Requires high T & PPowers stars & sun
Splitting a heavy nucleus into 2 nuclei with smaller mass #
Radioactive decay (w/o neutron)
Characteristics of Some Types of Radiation
Type Consists of Symbol ChargeMass (amu)
Common source
Penetrating power
Alpha radiation
Alpha particles (helium nuclei)
or
2+ 4
Radium-226
Low (0.05 mm body tissue)
Beta radiation
Beta particles (electrons)
or 1–1/1837 ~ 0
Carbon-14
Moderate
(4 mm body tissue)
Gamma radiation
High-energy electromagnetic radiation
0 0 Cobalt-60Very high (penetrates body easily)
Types of Nuclear Emissions/Radiation
Alpha Radiation
U23892
Uranium-238
Th +23490
Thorium-234
He ( emission)42
Alpha particle
Radioactivedecay
Mass # decreases by 4 & Atomic # decreases by 2
Beta Radiation
An electron resulting from the breaking apart of neutrons in an atom # of protons increases while #of neutrons decreases.Same Mass #; Atomic # increases by one
C146
Carbon-14 (radioactive)
N +147
Nitrogen-14 (stable)
e ( emission)0–1
Beta particle
→
n10
Neutron
p +11
Proton
e 0–1
Electron(beta
particle)
→
Gamma Radiation
Nuclei often emit gamma rays along with alpha or beta particles during radioactive decay.
Gramma ray – no mass/no electric charge - Does not alter the atomic number or mass number of an atom.
Ra +22688
Radium-226
Th23090
Thorium-230
He + 42
Alpha particle
Gamma ray
→
Pa +23491
Protactinium-234
Th23490
Thorium-234
e + 0–1
Beta particle
Gamma ray
→
Balancing Nuclear EquationsU-238 alpha decay- Helium particle emitted
23892U ? + 234
90Th
Na -24 beta decay- electron emitted
2411Na ? + 24
12Mg
Balancing Nuclear EquationsU-238 alpha decay- Helium particle emitted
23892U 4
2He + 23490Th
Na -24 beta decay- electron emitted
2411Na 0
-1e + 2412Mg
Nuclear Chemistry Application of Radioisotopes Smoke DetectorsFood IrradiationArchaeological DatingMedical UsesNuclear PowerNuclear Weapons
Applications of Nuclear Reactions
Nuclear power and Nuclear weapons
Most common nuclear fuel: Uranium-235, Plutonium-239
Difference btw power & weaponPower – can control E release & convert to heatWeapon – uncontrolled release of E
PowerNuclear energy – Fr ~80%, US 20%, Japan 35%, Germany –
30%
WeaponFission weapons – Atomic bombs (A-bomb)Fusion weapons – Hydrogen bombs (H-bomb)Manhattan Project WWIISubmarines – that use nuclear energy stay longer
underwater
A Few Pros and ConsNo more need for oilNot using fossil fuelFission > energy compared to
gasolineWill have unlimited amounts
of energy (esp if fusion works; sun)
No need for us to depend on other countries
Hard to controlNuclear wastePollutionRadiationNuclear reactor – away from large
population, waterways, earthquake zones
Japan reactor explosion – then cooling system fails so further explosion or leak of radioactive material can occur
Nuclear reactor overheating – explode like a nuclear weapon
Nuclear weapon – destructive potential
A half-life (t½) is the time required for one-half of the nuclei in a radioisotope sample to decay to products.
After each half-life, half of the original radioactive atoms have decayed into atoms of a new element.
Half-Life
Half-lives can be as short as a second or as long as billions of years.
Half-Lives of Some Naturally Occurring Radioisotopes
Isotope Half-life Radiation emitted
Carbon-14 5.73 × 103 years
Potassium-40 1.25 × 109 years
Radon-222 3.8 days
Radium-226 1.6 × 103 years
Thorium-234 24.1 days
Uranium-235 7.0 × 108 years
Uranium-238 4.5 × 109 years
Comparing Half-Lives
Half-LifeComparing Half-Lives
• The age of uranium-containing minerals can be estimated by measuring the ratio of uranium-238 to lead-206.
• Because the half-life of uranium-238 is 4.5 × 109 years, it is possible to use its half-life to date rocks as old as the solar system.
Uranium-238 decays through a complex series of unstable isotopes to the stable isotope lead-206.
Half Life CalculationsThe half-life of beryllium-11 is 13.81 seconds.
Let's say you start with 16 grams of 11Be. After 13.81s, you have 8 grams of that isotope left (the rest will have decayed to something else). After another 13.81s, you have 4 grams left; 13.81 seconds more, and you have 2 grams left……so after 3 half lives berllium-11 decayed from 16g to 2 g. In chemistry, you set up tables like this:
Time Amount remaining
0 s 16 grams
13.81 s 8 grams
27.62 s 4 grams
41.43 s 2 grams
Practice Problem…
In a particular bone sample, you have 80g of a parent and 560g of a daughter isotope. The half life of the sample is 100 years. How old is the bone?
560g + 80g = 640 g for the original parent640 320 160 80 equals 3 half lives(3)(100 yrs) = 300 years old
Now, you try some…
Closure:
Germany said it would close all of its 17 nuclear reactors by 2022, a sharp policy reversal that will make it the first major economy to quit atomic power in the wake of the nuclear crisis in Japan. Do you think USA should do the same?Provide 3 reasons to support your answer