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

Chain ReactionChain Reaction

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