Nuclear Chemistry.2 Chemistry Midland High School Mrs. Daniels 2007.2 Chemistry Midland High School Mrs. Daniels 2007.
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Nuclear ChemistryNuclear
Chemistry.2 Chemistry
Midland High School Mrs. Daniels 2007
.2 ChemistryMidland High School
Mrs. Daniels 2007
Back to the BeginningBack to the BeginningRecall the particles that make up an atom:Proton (+1 charge)Neutron (no charge)Electron (-1 charge)If you write out the symbol for an
element and include the atomic number and the atomic mass, it should look like this:
Recall the particles that make up an atom:Proton (+1 charge)Neutron (no charge)Electron (-1 charge)If you write out the symbol for an
element and include the atomic number and the atomic mass, it should look like this: 23
Na11
For sodium: the symbol is Nathe atomic mass is 23and the atomic # is 11
What information can you take from the following?
How many e-? P+? n0?e-=92 p+=92 n0=146
For sodium: the symbol is Nathe atomic mass is 23and the atomic # is 11
What information can you take from the following?
How many e-? P+? n0?e-=92 p+=92 n0=146
238 U 92
IsotopesIsotopes
What if I change the # of protons?It would be a different elementWhat if I change the # of electronsIt would be an ionWhat if I change the # of neutronsIt would be the same element, but a
different ISOTOPE of that element
What if I change the # of protons?It would be a different elementWhat if I change the # of electronsIt would be an ionWhat if I change the # of neutronsIt would be the same element, but a
different ISOTOPE of that element
HydrogenHydrogen
Let’s look at a couple of isotopes of hydrogen
The one on the left is referred to as “light” hydrogen and the one on the right is “heavy”
Which one is the “normal” hydrogen that we usually see
Let’s look at a couple of isotopes of hydrogen
The one on the left is referred to as “light” hydrogen and the one on the right is “heavy”
Which one is the “normal” hydrogen that we usually see
1 H1
2 H1
Variety of Isotopes Variety of Isotopes
Even though there are ~110 different elements listed on the periodic table, there are nearly 1500 different known isotopes of these elements
Some are stable and some “decay” or break apart over time
Even though there are ~110 different elements listed on the periodic table, there are nearly 1500 different known isotopes of these elements
Some are stable and some “decay” or break apart over time
Nuclear DecayNuclear Decay
All nuclear decay is accompanied by the emission of radiation
Spontaneous emission of radiation from an atom is called radioactivity
All elements have isotopes that are unstable and underdo decay to become other element
All nuclear decay is accompanied by the emission of radiation
Spontaneous emission of radiation from an atom is called radioactivity
All elements have isotopes that are unstable and underdo decay to become other element
Nuclear DecayNuclear Decay
Radioactive isotopes can emit three types of radiation:
Alpha particles: a helium nucleus (2 protons, 2 neutrons, with a charge of +2)Not very fast; can be blocked by
something as thin as a piece of paperBeta particles: fast moving electrons
created from the splitting of a neutron (into a proton and an electron)Requires aluminum foil 3mm thick to stop
Radioactive isotopes can emit three types of radiation:
Alpha particles: a helium nucleus (2 protons, 2 neutrons, with a charge of +2)Not very fast; can be blocked by
something as thin as a piece of paperBeta particles: fast moving electrons
created from the splitting of a neutron (into a proton and an electron)Requires aluminum foil 3mm thick to stop
Nuclear DecayNuclear Decay
Gamma rays: radiation that is NOT particles at all, but are invisible rays of energy with no mass or electrical chargeVery penetrating; need several cm of lead
or several meters of concrete to stopEmitting alpha or beta particles
changes the element into a new element
This is called nuclear transformation
Gamma rays: radiation that is NOT particles at all, but are invisible rays of energy with no mass or electrical chargeVery penetrating; need several cm of lead
or several meters of concrete to stopEmitting alpha or beta particles
changes the element into a new element
This is called nuclear transformation
DetectionDetection
How do we know that radiation is being released or emitted?
There are several types of “counters” used to detect radiation:
Geiger counter- uses Argon to transfer the radiation into a temporary electric pulse
Scintillation counter - uses sodium iodide to produce flashes of light when in contact with radiation
How do we know that radiation is being released or emitted?
There are several types of “counters” used to detect radiation:
Geiger counter- uses Argon to transfer the radiation into a temporary electric pulse
Scintillation counter - uses sodium iodide to produce flashes of light when in contact with radiation
Half - LifeHalf - Life
We can also go larger scale and look at the half life of various isotopes
Half life is defined as the time it takes for HALF of the sample of element to decay
For example, the half life of carbon-14 is 5,730 years
We can also go larger scale and look at the half life of various isotopes
Half life is defined as the time it takes for HALF of the sample of element to decay
For example, the half life of carbon-14 is 5,730 years
Half - LifeHalf - LifeCalculate how many years it would
take to decay 100g of carbon-14 into 12.5g.
Think on this: how many times was 100 cut in half to get to 12.5?
100 --> 5050 --> 2525 --> 12.5So… 3 half lives
Calculate how many years it would take to decay 100g of carbon-14 into 12.5g.
Think on this: how many times was 100 cut in half to get to 12.5?
100 --> 5050 --> 2525 --> 12.5So… 3 half lives
If each half life takes 5,730 years and we cut our sample in half three times, how long did it take?
5,730 x 3 = 17,190 yearsRoughly how much of a 100.0g
sample would be left after 1 year?Well, 50g will take 5,730 years to
decayA good estimate would be
that .0087g would decay each yearSo… 100.0-.0087 = 99.99gWe’d actually have to graph it to
determine this more accurately
If each half life takes 5,730 years and we cut our sample in half three times, how long did it take?
5,730 x 3 = 17,190 yearsRoughly how much of a 100.0g
sample would be left after 1 year?Well, 50g will take 5,730 years to
decayA good estimate would be
that .0087g would decay each yearSo… 100.0-.0087 = 99.99gWe’d actually have to graph it to
determine this more accurately
Radioactive DatingRadioactive Dating
Carbon-14, potassium-40, and others are isotopes can be used for dating objects from the past
We need to make the following assumptions for carbon dating:All living organisms contain the same ratio of
carbon-14 atoms and decay begins upon deathRemains of organisms or items created from
once living organisms contain the remaining amount of carbon-14, which can be measured
Carbon-14, potassium-40, and others are isotopes can be used for dating objects from the past
We need to make the following assumptions for carbon dating:All living organisms contain the same ratio of
carbon-14 atoms and decay begins upon deathRemains of organisms or items created from
once living organisms contain the remaining amount of carbon-14, which can be measured
Radioactive DatingRadioactive Dating
If we know the half life of carbon-14 is 5,730 years and we make the above assumptions, then we can compare the amount of carbon-14 in the sample with the amount of carbon-14 in a living organism
Then, we simply calculate how many half-lives the material underwent and multiply by 5,730 years per half life
Ta Daa! Now, we know how old it is…roughly
If we know the half life of carbon-14 is 5,730 years and we make the above assumptions, then we can compare the amount of carbon-14 in the sample with the amount of carbon-14 in a living organism
Then, we simply calculate how many half-lives the material underwent and multiply by 5,730 years per half life
Ta Daa! Now, we know how old it is…roughly
Fission and FusionFission and Fusion
With all the discussion of nuclear power…we HAVE to talk about fission and fusion.
Nuclear fusion: combining (FUSING together) two lighter nuclei to form a heavier nucleus
Nuclear fission: splitting a heavy nucleus into two smaller nuclei with smaller mass numbers
With all the discussion of nuclear power…we HAVE to talk about fission and fusion.
Nuclear fusion: combining (FUSING together) two lighter nuclei to form a heavier nucleus
Nuclear fission: splitting a heavy nucleus into two smaller nuclei with smaller mass numbers
Nuclear FissionNuclear Fission
Bombarding various isotopes with neutrons can cause an isotope to split into two lighter elements
The splitting is not always equal, so two different elements may be produced
Also, excess neutrons fly off during the splitting process and hit other atoms of the isotope
This begins several other fission reactions in the CHAIN of events
Bombarding various isotopes with neutrons can cause an isotope to split into two lighter elements
The splitting is not always equal, so two different elements may be produced
Also, excess neutrons fly off during the splitting process and hit other atoms of the isotope
This begins several other fission reactions in the CHAIN of events
Fission ContinuedFission Continued
A huge amount of energy can be released from nuclear fission reactions
For example, splitting one mole of uranium-235 is 26 million times the energy released from the combustion of one mole of methane
A huge amount of energy can be released from nuclear fission reactions
For example, splitting one mole of uranium-235 is 26 million times the energy released from the combustion of one mole of methane
Fission ContinuedFission Continued
If no neutrons go flying off and cause the chain reaction to keep going, then the reaction stops
If more than one neutron causes a new “chain” in the reaction, a build up of heat and an explosion can happen
The “critical mass” of fissionable material is needed to maintain a productive and constant fission reaction
If no neutrons go flying off and cause the chain reaction to keep going, then the reaction stops
If more than one neutron causes a new “chain” in the reaction, a build up of heat and an explosion can happen
The “critical mass” of fissionable material is needed to maintain a productive and constant fission reaction
Nuclear FusionNuclear FusionProduces even more energy than nuclear
fission; however, initiating the fusion reaction is much more difficult
Protons don’t want to come together because they repel each other
Temperatures of ~40 million K are estimated to be necessary to overcome the repulsion forces
Figure out a way to do it at more manageable temps (ie cold fusion) and you’ll be very rich and famous
Don’t forget to thank your high school chemistry teacher if this happens
Produces even more energy than nuclear fission; however, initiating the fusion reaction is much more difficult
Protons don’t want to come together because they repel each other
Temperatures of ~40 million K are estimated to be necessary to overcome the repulsion forces
Figure out a way to do it at more manageable temps (ie cold fusion) and you’ll be very rich and famous
Don’t forget to thank your high school chemistry teacher if this happens
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