Nuclear ChemistryNuclear Chemistry

Chapter 22Chapter 22

The NucleusThe Nucleus

Protons and neutrons are collectively referred to as nucleons.

In nuclear chemistry, an atom is referred to as a nuclide, and is identified by the number of protons and neutrons.

Nuclides can be written as 228 Ra or as Radium-228.

Protons and neutrons are collectively referred to as nucleons.

In nuclear chemistry, an atom is referred to as a nuclide, and is identified by the number of protons and neutrons.

Nuclides can be written as 228 Ra or as Radium-228.

88

An Error in Mass???An Error in Mass???

Since an atom is made up of protons, neutrons and electrons, you might assume that the mass of the atom would be equal to the sum of the individual subatomic particles.

Let’s look at 4 He: 2 protons: (2 x 1.007276 amu) 2 neutrons: (2 x 1.008665 amu) 2 electrons: (2 x 0.0005486 amu)

Since an atom is made up of protons, neutrons and electrons, you might assume that the mass of the atom would be equal to the sum of the individual subatomic particles.

Let’s look at 4 He: 2 protons: (2 x 1.007276 amu) 2 neutrons: (2 x 1.008665 amu) 2 electrons: (2 x 0.0005486 amu)

2

An Error in Mass???An Error in Mass???

When you add the components of the He atom, you get a mass of 4.032979 amu.

However, the atomic mass of He has been measured to be 4.00260 amu.

So, as you might have noticed the calculated mass is 0.03038 amu more than the actual mass.

How can this be so?

When you add the components of the He atom, you get a mass of 4.032979 amu.

However, the atomic mass of He has been measured to be 4.00260 amu.

So, as you might have noticed the calculated mass is 0.03038 amu more than the actual mass.

How can this be so?

Mass DefectMass Defect

The difference between the measured mass and the sum of its protons, neutrons and electrons is called the mass defect.

The differences in mass can be explained by Einstein’s equation :

E= mc2

The difference between the measured mass and the sum of its protons, neutrons and electrons is called the mass defect.

The differences in mass can be explained by Einstein’s equation :

E= mc2

E=mc2E=mc2

E stands for energym stands for the mass defectc2 stands for the speed of light

squaredIn order to use the equation, you

must convert amu to kg, to match the units for energy (kgm2/s2)

1 amu= 1.6605 x 10-27 kg

E stands for energym stands for the mass defectc2 stands for the speed of light

squaredIn order to use the equation, you

must convert amu to kg, to match the units for energy (kgm2/s2)

1 amu= 1.6605 x 10-27 kg

Calculating Nuclear Binding Energy

Calculating Nuclear Binding Energy

So using the example of 4He from before:

0.03038 amu x 1.6605 x 10-27 kg 1 amu equals 5.0446 x 10-29 kg.E= (5.0446 x 10-29 kg)(3.00 x 108

m/s)2

= 4.54 x 10-12 kgm2/s2 or J

So using the example of 4He from before:

0.03038 amu x 1.6605 x 10-27 kg 1 amu equals 5.0446 x 10-29 kg.E= (5.0446 x 10-29 kg)(3.00 x 108

m/s)2

= 4.54 x 10-12 kgm2/s2 or J

2

Nuclear Binding EnergyNuclear Binding Energy The nuclear binding energy, that we

just calculated for He, is the energy released when a nucleus is formed from nucleons.

This binding energy per nucleon is used to compare the stability of different nuclides.

To find the binding energy per nucleon, you simply divide the nuclear binding energy by the total number of nucleons present.

The nuclear binding energy, that we just calculated for He, is the energy released when a nucleus is formed from nucleons.

This binding energy per nucleon is used to compare the stability of different nuclides.

To find the binding energy per nucleon, you simply divide the nuclear binding energy by the total number of nucleons present.

Stability of the NuclideStability of the Nuclide

The higher the binding energy per nucleon, the more tightly the nucleons are held together.

Generally, the elements with intermediate atomic masses are those that are most stable.

The higher the binding energy per nucleon, the more tightly the nucleons are held together.

Generally, the elements with intermediate atomic masses are those that are most stable.

Band of StabilityBand of Stability When the number

of protons of stable nuclei are plotted against the neutrons, a belt-like graph is obtained.

When the number of protons of stable nuclei are plotted against the neutrons, a belt-like graph is obtained.

StabilityStability

Atoms that have low atomic numbers are most stable with a 1:1 neutron to proton ratio. ie: Helium

As the atomic number increases, the most stable ratio increases to 1.5:1. ie: Lead-206 has 124 neutrons to 82 protons (1.51:1 ratio).

Atoms that have low atomic numbers are most stable with a 1:1 neutron to proton ratio. ie: Helium

As the atomic number increases, the most stable ratio increases to 1.5:1. ie: Lead-206 has 124 neutrons to 82 protons (1.51:1 ratio).

Strong Nuclear ForceStrong Nuclear Force

The trend in stability is explained by the relationship between the nuclear force and the electrostatic forces between protons.

You know that protons repel each other as far as the electrostatic force goes. (“like repels like”).

The strong nuclear force allows protons to be attracted, but only to protons that are close to one another.

The trend in stability is explained by the relationship between the nuclear force and the electrostatic forces between protons.

You know that protons repel each other as far as the electrostatic force goes. (“like repels like”).

The strong nuclear force allows protons to be attracted, but only to protons that are close to one another.

Strong Nuclear ForceStrong Nuclear Force

As the atomic number increases, the electrostatic force between protons increases more quickly than the nuclear force.

More neutrons are required to strengthen the strong nuclear force.

However, beyond the atomic number 83 (Bismuth), no stable nuclides exist.

As the atomic number increases, the electrostatic force between protons increases more quickly than the nuclear force.

More neutrons are required to strengthen the strong nuclear force.

However, beyond the atomic number 83 (Bismuth), no stable nuclides exist.

Magic NumbersMagic Numbers

Stable nuclei tend to have even numbers of nucleons.

This is because the nucleus is most stable when nucleons (like electrons) are paired!

The most stable nuclides are those that have 2, 8, 20, 28, 50, 82, or 126 protons, neutrons or total nucleons.

Stable nuclei tend to have even numbers of nucleons.

This is because the nucleus is most stable when nucleons (like electrons) are paired!

The most stable nuclides are those that have 2, 8, 20, 28, 50, 82, or 126 protons, neutrons or total nucleons.

Nuclear Shell ModelNuclear Shell Model

This theory says that nucleons exist in different energy levels, or shells, in the nucleus.

2, 8, 20, 28, 50, 82, 126 are representative of completed nuclear energy levels and are called magic numbers.

This theory says that nucleons exist in different energy levels, or shells, in the nucleus.

2, 8, 20, 28, 50, 82, 126 are representative of completed nuclear energy levels and are called magic numbers.

Nuclear ReactionsNuclear Reactions

A nuclear reaction, or nuclear decay reaction, is a reaction that affects the nucleus of an atom.

Unstable nuclei undergo spontaneous changes that change the number of protons and neutrons in an atom.

Large amounts of energy are given off in this process.

A nuclear reaction, or nuclear decay reaction, is a reaction that affects the nucleus of an atom.

Unstable nuclei undergo spontaneous changes that change the number of protons and neutrons in an atom.

Large amounts of energy are given off in this process.

How to Solve Nuclear Reactions

How to Solve Nuclear Reactions

1) Remember that the total of atomic numbers and mass numbers should be the same on each side of the equation.

*Notice that when the atomic number (number of protons) changes, the identity of the element changes. This is called transmutation.

1) Remember that the total of atomic numbers and mass numbers should be the same on each side of the equation.

*Notice that when the atomic number (number of protons) changes, the identity of the element changes. This is called transmutation.

Helpful symbolsHelpful symbols

Neutrons are represented as 1n

Electrons are represented as 0e

Protons are represented as 1p

Neutrons are represented as 1n

Electrons are represented as 0e

Protons are represented as 1p

0

-1

1

Examples:Examples:

212Po 4He + _____

Mass number: 212 - 4 = 208 Atomic number: 84 - 2 = 82

So the missing nuclide must have a mass of 208 and an atomic number of 82.

Answer: 208Pb

212Po 4He + _____

Mass number: 212 - 4 = 208 Atomic number: 84 - 2 = 82

So the missing nuclide must have a mass of 208 and an atomic number of 82.

Answer: 208Pb

84 2

82

Complete these on your own:

Complete these on your own:

1)

2)

3)

1)

2)

3)

History of Radioactive Decay

History of Radioactive Decay

1896- Henri Becquerel discovered radioactivity when a uranium compound was left on a photographic plate.

1896- Henri Becquerel discovered radioactivity when a uranium compound was left on a photographic plate.

Even though the plate was protected from sun exposure, it was still exposed due to the radioactive x-rays given off by uranium.

Even though the plate was protected from sun exposure, it was still exposed due to the radioactive x-rays given off by uranium.

Radioactive DecayRadioactive Decay

Defined: the spontaneous disintegration of a nucleus into a slightly lighter nucleus, accompanied by the emission of particles, electromagnetic radiation, or both.

Defined: the spontaneous disintegration of a nucleus into a slightly lighter nucleus, accompanied by the emission of particles, electromagnetic radiation, or both.

This is what happened to the photographic plate in Becquerel’s experiment.

This is what happened to the photographic plate in Becquerel’s experiment.

The Curies The Curies

Marie and Pierre found that of the elements known in 1896, only uranium and thorium were radioactive.

Marie is credited with the discovery of Radium and Polonium, both of which are also radioactive.

Marie and Pierre found that of the elements known in 1896, only uranium and thorium were radioactive.

Marie is credited with the discovery of Radium and Polonium, both of which are also radioactive.

Types of Radioactive Decay

Types of Radioactive Decay

Type Symbol Charge Mass (amu)

Alpha particle

+2 4.00260

Beta particle

-1 0.0005486

Positron +1 0.0005486

Gamma ray

0 0

Alpha EmissionAlpha Emission

An alpha particle has 2 protons and 2 neutrons bound together and is emitted during some types of nuclear decay.

They can be stopped by clothing or paper because they are so large.

Example reaction:

An alpha particle has 2 protons and 2 neutrons bound together and is emitted during some types of nuclear decay.

They can be stopped by clothing or paper because they are so large.

Example reaction:

Beta EmissionBeta Emission

A beta particle is an electron emitted from the nucleus during some kinds of radioactive decay.

They can be stopped by aluminum foil or thin metals.

Example reaction:

A beta particle is an electron emitted from the nucleus during some kinds of radioactive decay.

They can be stopped by aluminum foil or thin metals.

Example reaction:

Positron EmissionPositron Emission

A positron is a particle that has the same mass as an electron but has a positive charge.

They can be stopped by aluminum foil and thin metals as well.

Example reaction:

A positron is a particle that has the same mass as an electron but has a positive charge.

They can be stopped by aluminum foil and thin metals as well.

Example reaction:

Electron CaptureElectron Capture

In electron capture, an inner orbital electron is captured by the nucleus of its own atom.

Example reaction:

In electron capture, an inner orbital electron is captured by the nucleus of its own atom.

Example reaction:

Gamma EmissionGamma Emission

Gamma rays are high-energy electromagnetic waves emitted from a nucleus as it changes from an excited state to a ground state.

Gamma rays are high-energy electromagnetic waves emitted from a nucleus as it changes from an excited state to a ground state.

Gamma RaysGamma Rays Unlike the other

forms of radiation we have discussed, it takes a lot to stop gamma rays from penetrating your skin.

Dense materials, like lead or concrete, are used to stop gamma rays.

Unlike the other forms of radiation we have discussed, it takes a lot to stop gamma rays from penetrating your skin.

Dense materials, like lead or concrete, are used to stop gamma rays.

Decay SeriesDecay Series

Most of the decay reactions we have studied thus far only involve one transformation.

However, it is often necessary for a series of these reactions to occur before a stable nuclide is reached.

Most of the decay reactions we have studied thus far only involve one transformation.

However, it is often necessary for a series of these reactions to occur before a stable nuclide is reached.

The heaviest nuclide of each series is called the parent nuclide.

All the nuclides produced by the parent are called daughter nuclides.

The heaviest nuclide of each series is called the parent nuclide.

All the nuclides produced by the parent are called daughter nuclides.

Uranium-238 Decay SeriesUranium-238 Decay Series

Artificial TransmutationsArtificial Transmutations

Some radioactive nuclide cannot be found naturally on the earth, so they are called artificial radioactive nuclides.

Some radioactive nuclide cannot be found naturally on the earth, so they are called artificial radioactive nuclides.

They are made by bombardment of stable nuclei with charged and uncharged particles.

They are made by bombardment of stable nuclei with charged and uncharged particles.

Rutherford’s apparatus

Artificial TransmutationsArtificial Transmutations

Neutrons are often used because of their neutral charge.

Neutrons are often used because of their neutral charge.

When alpha particles or protons are used, they must be accelerated to obtain the energy needed to approach the positively charged nucleus.

When alpha particles or protons are used, they must be accelerated to obtain the energy needed to approach the positively charged nucleus.

Getting Radioactive elements

Getting Radioactive elements

Some radioactive substances are found in nature.

However, some can be created through artificial transmutation.

Some radioactive substances are found in nature.

However, some can be created through artificial transmutation.

Examples: Examples:

Radiation ExposureRadiation Exposure Roentgen- unit used to measure nuclear

radiation, equal to the amount of radiation that produces 2x 109 ion pairs when it passes through 1 cm3 of dry air.

rems- (roentgen equivalent, man) measures radiation damage to human tissue

1 rem is the quantity of ionizing radiation that does as much damage to human tissue as 1 roentgen of high voltage X-rays.

Roentgen- unit used to measure nuclear radiation, equal to the amount of radiation that produces 2x 109 ion pairs when it passes through 1 cm3 of dry air.

rems- (roentgen equivalent, man) measures radiation damage to human tissue

1 rem is the quantity of ionizing radiation that does as much damage to human tissue as 1 roentgen of high voltage X-rays.

Exposure to RadiationExposure to Radiation

The long term effects of continued radiation damage include cancer and DNA mutations, causing genetic abnormalities.

Everyone is exposed to background radiation. The amount of exposure depends on certain activities. The average exposure in one year is 0.1 rem. The maximum permissible dose is 0.5 rem per year.

http://www.epa.gov/rpdweb00/understand/calculate.html

The long term effects of continued radiation damage include cancer and DNA mutations, causing genetic abnormalities.

Everyone is exposed to background radiation. The amount of exposure depends on certain activities. The average exposure in one year is 0.1 rem. The maximum permissible dose is 0.5 rem per year.

http://www.epa.gov/rpdweb00/understand/calculate.html

Radiation SicknessRadiation Sickness The larger the dose received at once the

greater the effect on the whole body. Generally- 25 rem and under cannot be

detected 100 rem reduces white blood cell count

temporarily >100 rem person experiences nausea,

vomiting and a reduction in white blood cell count

>300 rem white cell count at zero and diarrhea, hair loss and infection occur

The larger the dose received at once the greater the effect on the whole body.

Generally- 25 rem and under cannot be detected

100 rem reduces white blood cell count temporarily

>100 rem person experiences nausea, vomiting and a reduction in white blood cell count

>300 rem white cell count at zero and diarrhea, hair loss and infection occur

Lethal DoseLethal Dose

The lethal dose of a substance is often referred to as LD50. This means that it is expected to cause death in 50% of the people with exposure.

The LD50 for humans of radiation is 500 rems.

Dosages of 600 rem would be fatal to all humans within a few weeks.

The lethal dose of a substance is often referred to as LD50. This means that it is expected to cause death in 50% of the people with exposure.

The LD50 for humans of radiation is 500 rems.

Dosages of 600 rem would be fatal to all humans within a few weeks.

LD50 for life forms other than humans

LD50 for life forms other than humans

Insects- 100,000 remsBacterium- 50,000 remsRat- 800 remsHumans- 500 remsDog- 300 rems

Insects- 100,000 remsBacterium- 50,000 remsRat- 800 remsHumans- 500 remsDog- 300 rems

Detecting radiation in your surroundings

Detecting radiation in your surroundings

Geiger counter- detect radiation by counting electric pulses, kind of sounds like a metal detector

Film Badges- used to measure exposure of people working with radiation

Geiger counter- detect radiation by counting electric pulses, kind of sounds like a metal detector

Film Badges- used to measure exposure of people working with radiation

Cloud ChambersCloud Chambers

Used to detect alpha and beta particles

Chamber is filled with ethanol or water vapor. When the particles collide with air, ions are formed.

Used to detect alpha and beta particles

Chamber is filled with ethanol or water vapor. When the particles collide with air, ions are formed.

The vapor condenses around the path of ions and makes it visible.

The vapor condenses around the path of ions and makes it visible.

Applications of nuclear Chemistry

Applications of nuclear Chemistry

1) Radioactive dating- age is measured by accumulation of daughter nuclides or disappearance of parent nuclides

1) Radioactive dating- age is measured by accumulation of daughter nuclides or disappearance of parent nuclides

2) Radioactive tracers- radioactive atoms included in substances so that movement can be followed by radiation detectors

ie: technetium-99 can be used to detect bone cancer.

2) Radioactive tracers- radioactive atoms included in substances so that movement can be followed by radiation detectors

ie: technetium-99 can be used to detect bone cancer.

Applications of Nuclear Chemistry

Applications of Nuclear Chemistry

3) Irradiation of food

Using radiation to kill bacteria on food, like produce- tomatoes, blueberries, mushrooms, and even spinach

3) Irradiation of food

Using radiation to kill bacteria on food, like produce- tomatoes, blueberries, mushrooms, and even spinach

This is in response to the food borne illnesses that have been plaguing the US.

E. coli Listeria Salmonella

This is in response to the food borne illnesses that have been plaguing the US.

E. coli Listeria Salmonella

Radiation Doses for Therapeutic Procedures

Radiation Doses for Therapeutic Procedures

Lymphoma- 4500 rem

Skin cancer- 5000-6000 rem

Lung cancer- 6000 rem

Brain tumor- 6000-7000 rem

Lymphoma- 4500 rem

Skin cancer- 5000-6000 rem

Lung cancer- 6000 rem

Brain tumor- 6000-7000 rem

Remember that these are not whole body dosages.

Many external beam cancer treatments are targeted to specific areas of the body.

Remember that these are not whole body dosages.

Many external beam cancer treatments are targeted to specific areas of the body.