nuclear chemistry nucleus is held together by “strong” or “nuclear” forces. –strongest...

Nuclear Chemistry• Nucleus is held together by “strong” or “nuclear”

forces. – Strongest forces in the universe

– Between like charges

– The closer the charged particles, the stronger the force

• Too many neutrons can get in the way of this force and make the nucleus unstable.

• “Neutron-Heavy” isotopes stabilize in two ways:– Emitting small amounts of radioactivity

– Flying apart with great amounts of energy

Spontaneous Radioactive Decay

• Nucleus spontaneously changes structure to reduce the number of neutrons and become more stable.– Alpha particle emission

– Beta particle emission

– Gamma ray emission

Alpha Decay

• Atomic number decreases by 2

• Element changes - transmutation

Beta Decay

-

• Atomic number INCREASES by 1

• Element changes - transmutation

Gamma Radiation

• Emission of gamma rays (γ)

• Very high energy light waves with high frequency

• Non-particulate in nature

• Mass is lost!!!

Half-Life• Time required for half an amount of isotope

to decay• Varies from fractions of a second to billions

of years

• Formula:

• Practice: If you have 10 Kg of radioactive Barium and the half-life is 13 days, how much barium will be left after 100 days?

Applications of Radioactivity• Smoke detectors

– Use americium

• Medicine– Imaging and analysis– Cancer treatment

• Determining the age of the earth– U-238 present in rocks slowly

decays to Pb-206– The age of the earth is:

4.5 billion years!!!

NUCLEAR FISSION• Nucleus of a radioactive element splits by

bombardment from an external source

• Simultaneous release of large amounts of energy, in the form of heat, light and sound – Exothermic Process!!

Nuclear FissionNeutron induced to U235

The sum of the masses of the resulting nuclei is about 0.1% less than the original mass

The “missing mass” is converted to energy according to E=mc2

Chain ReactionsThree neutrons are released and may:

• Cause another fission by colliding with a U235 nucleus. If enough neutrons are present a chain reaction will occur.

• Called the Critical Mass

• Each split released a large amount of ENERGY!

• Be absorbed in other material

• Get lost in the system

Destructive Fission Reactions• Chernobyl

• Atomic Bombs dropped on Japan

Nuclear Fission Power• Similar to Coal power

• Heat is generated by a fission reaction rather than from the burning of coal

• Benefits: cheaper after setup, uses very little fuel

• Drawbacks: can be dangerous if reaction is not controlled, creates radioactive waste

Nuclear Reactors• Control rods absorb

neutrons to control the rate of reaction.

• Nuclear subs use this technology so they do not have to transport gasoline or coal.

Nuclear Fusion• Multiple nuclei join together to form a heavier nucleus. • Releases of large amounts of energy.• The sun converts hydrogen to helium in a fusion reaction.

This is the source of most of our ENERGY

Fusion Power• Benefits: uses plentiful

hydrogen, creates very large amounts of energy

• Drawbacks: – requires massive amounts of

heat to start the reaction– Too little mass to create a

sustained reaction• Uses of fusion already:

– Sun– Hydrogen bomb

• never used in wartime• 10X power of atomic bomb• Initial heat produced by a small

atomic bomb inside• Hydrogen Bomb Video

Innovations in Nuclear Chemistry

• Particle accelerators – “atom smashers”

• Large Hadron Colider – CERN– Opened Sept. 09, 2008