What do they have in common?What do they have in common?

Nuclear Chemistry

Nuclear ReactionsNuclear Reactions Involve the

nucleus Radioactivity is

the spontaneous emission of radiation from an atom

Nuclear StabilityNuclear Stability Most atoms have a

stable nucleus A strong nuclear force

holds protons and neutrons together

Neutrons act as the “glue” holding the protons together

Figure 18.1 The Zone of Stability

Belt of Nuclear Belt of Nuclear StabilityStability

There seems to be a ratio of protons to neutrons that increase the chances that an atom will be stable.

Types of RadiationTypes of Radiation The three main types of nuclear radiation

are alpha radiation, beta radiation, and gamma radiation.

Radioactive ParticlesRadioactive Particles Alpha particleAlpha particle - Helium nucleus - Helium nucleus

with no electronswith no electrons +2 charge+2 charge Beta particleBeta particle - High energy stream - High energy stream

of electronsof electrons -1 charge-1 charge Gamma RaysGamma Rays - High energy wave - High energy wave

which are the strongestwhich are the strongest No chargeNo charge Refer to the radioactive particle Refer to the radioactive particle

sheet that can be found on the sheet that can be found on the website for other particles.website for other particles.

A look at Alpha Decay

A look at Beta Decay

A look at Gamma Decay

Penetrating PowersPenetrating Powers

Nuclear EquationsNuclear Equations Scientists use a nuclear equation Scientists use a nuclear equation

when describing radioactive decaywhen describing radioactive decay

The mass number and atomic The mass number and atomic number must add up to be the same number must add up to be the same on both sides of the equationon both sides of the equation

Balancing Nuclear EquationsBalancing Nuclear Equations Here’s the equation from the previous slide. Here’s the equation from the previous slide.

The top numbers on the left side of the The top numbers on the left side of the arrow = the top numbers on the right side arrow = the top numbers on the right side of the arrow.of the arrow.

The same holds for the bottom numbers.The same holds for the bottom numbers. USE A PERIODIC CHART for the atomic USE A PERIODIC CHART for the atomic

numbers if needed.numbers if needed.

Beta DecayBeta Decay Beta decay results in an increase in Beta decay results in an increase in

the atomic number.the atomic number.

Notice how the top numbers equal Notice how the top numbers equal and the bottom numbers also and the bottom numbers also equalequal

Nuclear Stability and DecayNuclear Stability and Decay

For the equations onthe right, the atomic numbers are also shown but in many equationsthey are omitted because they can be found on the periodic chart.

For example, carbon is often written as: 14C

PracticePracticeWrite the nuclear equation of

the alpha decay of Radon – 226Write the nuclear equation of

the alpha decay of Gold – 185The number after the element

is the mass number.

Practice AnswersPractice Answers226Rn 4He + 222Po

185Au 4He + 181Ir

PracticePractice Write the nuclear equation of the

beta decay of Iodine - 131 Write the nuclear equation of the

beta decay of Sodium - 24

Practice AnswersPractice Answers 131I -1e-1 + 131Xe

24Na -1e-1 + 24Mg

Half LifeHalf LifeRadioisotopes are radioactive

isotopes of elements (not all isotopes are radioactive)

A half-life is the amount of time it takes for one half of a sample to decay.

The half-life is different for each element and isotope.

http://www.colorado.edu/physics/2000/isotopes/radioactive_decay3.html

Beta Decay of Phosphorous Beta Decay of Phosphorous - 32- 32

Notice that every 14 days, the amount is cut in half.

Radiocarbon DatingRadiocarbon Dating Carbon - 14 undergoes

beta decay to form stable nitrogen 14

Half life of 5,730 years Used to approximate

ages 100 – 30,000 years Other radioisotopes are

used to measure longer periods of time

Parent and Daughter Parent and Daughter NuclidesNuclides

The term parent nuclide refers to the original atom.

The term daughter nuclide refers to the particle that is produced after the radioactive decay is completed.

Parent Daughter Half Change in...

Carbon-14 Nitrogen-14 5730 years

Uranium-235 Lead-207 704 million years

Uranium-238 Lead-206 4,470 million years

Potassium-40 Argon-40 1,280 million years

Thorium-232 Lead-208 14,010 million years

Rubidium-87 Strontium-87 48,800 million years

Some examples of Parent – Daughter Nuclides

PracticePracticeThe half-life of Po-218 is three

minutes. How much of a 2.0 gram sample remains after 15 minutes?

Remember that the symbol for half life is t1/2

Practice AnswerPractice Answer It is often best to set up a simple

table especially if the amount of time is a multiple of the half life like in this example.

Notice that 15 minutes is a multiple of the 3 minute half – life.

The next slide has the table that we need to create to solve the problem.

Practice Answer: Half – Life Practice Answer: Half – Life TableTable

Amount of Material Initially

Time elapsed Amount of material remaining

2 grams 0 minutes 2 grams2 grams 3 minutes 1 gram1 gram 6 minutes .5 grams.5 gram 9 minutes .25 grams

.25 grams 12 minutes .125 grams.125 grams 15 minutes .0625 grams

So after 15 minutes, there is only .0625 grams left.

PracticePracticeThree grams of Bismuth-218

decay to 0.375 grams in one hour.

What is the half-life of this isotope?

Practice Answer Half – Life Practice Answer Half – Life TableTable

Amount of Material Initially

Number of half-lives

Amount of material remaining

3 grams 1 1.5 grams1.5 grams 2 .75 grams.75 grams 3 .375 grams

We can also create the table going backwards to answer questions like this one.

Notice it is really a similar table.

It took 3 half-lives to get to the amount .375 grams. If 1 hour equals 3 half-lives, then each half-life must be 20 minutes.

More on Half - LifeMore on Half - Life Sometimes the amount of time is

not a multiple of number of half-lives.

We can use the following equation for all half-life problems.

Nuclear Nuclear BombardmentBombardment

Nuclear scientists change elements by Nuclear scientists change elements by bombarding the nucleus with particles – bombarding the nucleus with particles – transmutationtransmutation

1414N + N + 44He He 1717O + O + 11HH Leads to the creation of transuranium Leads to the creation of transuranium

(after U) elements.(after U) elements.

Transmutation ReactionsTransmutation Reactions The first artificial transmutation reaction The first artificial transmutation reaction

involved bombarding involved bombarding nitrogen gas with gas with alpha particles.alpha particles.

Fermilab Particle Fermilab Particle AcceleratorAccelerator

Nuclear PowerNuclear Power Nuclear Reactors use fission of Uranium-

235 as source of energy A large nucleus is split into two smaller

nuclei A small amount of mass is converted to a

tremendous amount of energy (E = mc)2

About 1 kg of Uranium-235 = 2.2 million gallons of gasoline

http://people.howstuffworks.com/nuclear-power2.htm

Nuclear FissionNuclear Fission Nuclear FissionNuclear Fission

Fission Produces a Chain Reaction

Overview of a nuclear power plant

All power plants work on the same principal. It needs to heat up water to make steam to run a steam engine which produces the actual electricity. The only difference between a coal power plant and a nuclear power plant is that the first burns coal to heat the water and the second controls a nuclear reaction to heat the water.

Nuclear Power Plants # 1• A nuclear plant has some differences

of course compared to a coal burning plant.• The fuel is much more costly, though lasts much longer.• The heat can be controlled easily in a coal burning plant by simply controlling how much coal is added to the fire. • This is the primary difference and the biggest safety concern in a nuclear power plant as the next slide shows.

Nuclear Power Plants # 2 Uranium fuel can’t be removed or limited

like a coal fired power plant. The heat comes from the chemical reaction

of the decay of a uranium atom. The atom splits and the chain reaction

keeps it going. The way to control the heat released is by

controlling the neutrons released during the chain reaction.

This is done by using graphite rods that can be raised and lowered which controls the amount of neutrons absorbed at any time.

Nuclear Power Plants # 3•This was the primary problem in developing

the atomic bomb during World War 2.Both sides knew how to get the fission process of the uranium going, but the questions were on how to keep it under control so it wouldn’t go off too early in the lab.

There were two teams. One team was working for Germany. The other team was a group of mostly German scientists who were able to flee Germany to the United States and were working for the Allied forces.

The team working in Germany focused on using heavy water to moderate the chain reaction. Heavy water is regular water but with a difference in the hydrogen isotope. Regular water is mostly 1H but heavy water is 2H. This extra neutron helps to absorb other neutrons and control the reaction. Regular water is about .0001 % heavy water but the percentage needed is about 98 % so it took time to get enough heavy water needed.

Nuclear Power Plants # 4

Nuclear Power Plants # 5The allied side, based in the United

States decided to use graphite rods which could be raised and lowered and absorb the neutrons.

While both were acceptable ways to moderate the reaction, the Allied side was able to create the bomb first and force an end to the war.

A Schematic Diagram of a Reactor Core

Gun-triggered fission bomb (Little Boy - Hiroshima)

Implosion-triggered fission bomb (Fat Man - Nagasaki)

http://people.howstuffworks.com/nuclear-bomb5.htm

Nuclear Power Plants # 6An interesting side note to all of this is how

nuclear energy in power plants came to be.

The scientists who were working on the bomb were uneasy with this type of power and the US government put out a survey to ask how can this energy source by used peacefully. Some answers such as to create a new Panama Canal were tossed aside (too much residual radiation). Suggestions were that if the reaction can be controlled it can be used to run steam turbines in power plants.

This led to the start of the nuclear power plant.

A schematic of a nuclear power plant

What the heat from the radioactive process does is to heat water to run a turbine.

Nuclear FusionNuclear Fusion Atomic nuclei fuse releasing a

tremendous amount of energy

Nuclear WeaponsNuclear Weapons The bombs dropped in World War 2 were

fission bombs made of Uranium and getting their energy when the Uranium atoms split (fission) into smaller atoms. This is called an Atomic Bomb.

Since then, the process of taking Hydrogen atoms and combining 4 of them to create a Helium atom (fusion) has been developed. This creates a more powerful bomb.

This is called a Nuclear Bomb.

Radiation and YouRadiation and You SI units are in Curies (Ci) One Curies is amount of nuclear

disintegrations per second from one gram of radium

Also measured in rem (Roentgen Equivalent for Man)

Over 1000 rem is fatal The next slide gives a glimpse of the

radiation we receive. NOTE that the units are MILLIREMS, which is 1/ 1,000 of a REM.

Radon GasRadon Gas

Figure 18.2 A Decay Series

Detecting Nuclear RadiationDetecting Nuclear Radiation You cannot hear or

feel nuclear radiation.

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