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