Nuclear Chemistry

Nuclear Chemistry can be used to produce electrical power, diagnose and treat disease, and has been used for weapons which have changed the world forever.

Nuclear Power Plants

Here, a nuclear fission reaction is used to produce large amounts of energy via generation of steam.

It also produces waste that is radioactive.

Many medical tests and treatments involve the use of radioactive substances. Here, Homer Simpson’s brain is illuminated to show his skull in an X-ray.

Nuclear Medicine

Characteristics of Chemical and Nuclear Reactions

Chemical Reactions Nuclear Reactions

1. Occur when bonds are broken and formed.

1. Occur when nuclei emit particles and/or rays.

2. Atoms remain unchanged, though they may be rearranged.

2. Atoms are often converted into atoms of another element.

3. Involve only valance (outer) electrons.

3. May involve protons, neutrons, and electrons.

4. Associated with small energy changes.

4. Associated with large energy changes.

5. Reaction rate is influenced by temperature, pressure, concentration, and catalysts.

5. Reaction rate is not normally affected by temperature, pressure, or catalysts.

History

• 1895 – William Roentgen discovered that when certain ores (rocks) were hit by electrons, they gave off invisible rays that would cause photographic film to darken. He named them X-rays.

• 1903- Marie Curie and her husband Pierre discovered that Uranium atoms in rocks emit rays and she named this process radioactivity. The particles and rays given off she called radiation.

• Radioactivity- is the process in which some substances emit radiation.

• Radiation – the rays of energy and particles (alpha, beta, and gamma) that are emitted by radioactive materials.

• Radioactive atoms emit radiation because their nuclei are unstable. Unstable nuclei lose energy by emitting radiation in a spontaneous process called radioactive decay.

Types of Radiation

• AlphaAlpha ( ())

• BetaBeta ( ())

• GammaGamma ( ())

These particles are shown are your STAAR These particles are shown are your STAAR EOC formula chart in case you need them!EOC formula chart in case you need them!

Alpha (Alpha () ) radiation – occurs when alpha particles are emitted. An alpha particle is a helium nucleus. It has the symbol 4

2He or α. During alpha decay, a nucleus loses 2 neutrons and 2 protons, to become a new element.

Alpha (() ) decay

He Pb Po2

4

82

206

84

210

Beta (Beta () ) radiation – consists of fast moving electrons called beta particles. Each beta particle is an electron with a 1- charge. Beta decay changes a eta decay changes a nn00 into a p+ and an e-. into a p+ and an e-.

Beta (() ) Decay - occurs when an isotope is unstable due to having too many neutrons.

e N C1-

0

7

14

6

14

• Gamma (Gamma () ) radiation – Gamma rays are high energy radiation that have no mass and no electrical charge. They are not deflected (bent) by electric or magnetic fields. Gamma rays usually accompany alpha and beta radiation and they account for most of the energy lost during the radioactive decay process. Because gamma rays have no mass, they cannot result in the formation of a new atom.

TYPE TYPE SYMBOL SYMBOL ATOMIC # ATOMIC # CHANGE CHANGE

NEUTRON NEUTRON CHANGE CHANGE

MASS MASS CHANGE CHANGE

ALPHA (ALPHA ())

BETA BETA (())

GAMMA GAMMA (())

by 2 by 2 HeHe4422

+2+2 by 2 by 2 by 4 by 4

ee 00-1-1 by 1 by 1 by 1 by 1 no change no change

no change no change no change no change no change no change 00 00

Penetrating Power of Radiation

The above diagram shows how different types of radiation can penetrate through different materials. The most energeticradiation, gamma, γ, can penetrate most materials. Only lead and concrete are dense enough to stop most of it! Gamma rays and X-rays are similar in their energies. Have you ever worn a lead vest to protect yourself from X-rays? Dentists use them to protect you from these rays, which can harm you.

Symbolic Notation

For element symbol X, the mass, m, is the superscript. It equals the protons + neutrons.

The atomic number, a, of the isotope is the number of protons.

A radioisotope just means it’s radioactive. All elements with atomic numbers greater than 83 are radioactive.

a

mX

Writing and BalancingNuclear Equations

• In balancing nuclear equations, mass numbers and atomic numbers are conserved.

• This means, simply, that the sum of the subscripts (atomic numbers) on one side of the reaction will equal the sum of the subscripts on the other side.

• The same will be true for the superscripts

(mass numbers).

Balancing Nuclear Equations• Fill in the missing particle:

– 10n 1

1p + ____

– 20882Pb 0

-1e + _____

– 23892U 234

90Th + _____ + 200γ

– 22688Ra 4

2He + _____

Radium was identified in 1898 by Marie and Pierre Curie.

Transmutation• Transmutation is when an atom of one type changes to an atom of

a different type.

• So far, the nuclear reactions we have seen occur spontaneously. That is, they occur “on their own.” Radioactive elements decay naturally.

• For example, radium is an element that occurs naturally in an ore called “pitchblende.”

• Radium undergoes alpha decay to form radon, a noble gas. Radon is a radioactive gas that seeps up from the earth.

22688Ra 222

86Rn + 42He

Induced Transmutation• Induced transmutation occurs when one particle is bombarded, or hit,

with another particle and transmutation then occurs.

• Scientists do this in “atom smashers” or particle accelerators.

• All elements beyond uranium on the periodic table have been produced this way.

Ex: 23892U + 1

0n 23993Np + 0

-1β

Ex: 23994Pu + 4

2He 10n + 243

96Cm

• Notice that in the above reactions, mass numbers and atomic numbers are conserved. (Totals are the same on both sides.)

Fusion

• Fusion is a nuclear reaction in which atomic nuclei are combined.

• The sun is powered by fusion reactions.

• Within the Sun, hydrogen atoms fuse together to form helium atoms and release GINORMOUS amounts of energy!

Fission

• Fission means the splitting of atoms into fragments• Nuclear power plants use fission to produce electrical

power.• The most famous example is when uranium-235 is

bombarded with neutrons to form other, smaller isotopes, as well as more neutrons.

• These neutrons then go on to strike other uranium atoms in what is known as a “chain reaction”. The reaction is controlled by “control rods”

• The explosion of an atom bomb is an example of an uncontrolled chain reaction.

Atomic BombsFission was used to make atomic bombs

used during World War II!

Little Boy

Little Boy was the name of the bomb exploded over Hiroshima 1945, killing thousands of Japanese.

Radioactive Decay

• Radioactive elements are still around after 15 billion years. Why?

• Because some of them decay very, very slowly.

• The half-life of an isotope is defined as the time it takes for one-half of a radioisotope’s nuclei to decay.

Radiation Safety

• Radioactive waste from nuclear power plants must be stored underground, and will remain radioactive for hundreds or years or even longer

• Both X-rays and gamma rays are very damaging to living tissues.