nuclear chemistry

Nuclear Chemistry

Nuclear Reactions• Nuclear reactions change an atom’s nucleus.• 3 Types of radiation are produced from

nuclear reactions: alpha, beta & gamma.–Alpha: positive–Beta: negative–Gamma: no charge

• Strong nuclear force: force that holds the protons together in the nucleus• Neutrons add a strong nuclear force

to a nucleus, which keeps the protons from breaking the nucleus apart.• All nuclei with atomic numbers >83

are radioactive.

• Beyond 20 protons, nuclei need many more neutrons than protons to be stable.• Nuclei can become unstable if there

are too many or too few neutrons.• Isotopes that are much heavier or

much lighter than the most common isotope are likely to be radioactive.

Alpha Particles• An alpha (α) particle has 2 neutrons & 2

protons and is identical to a He-4 nucleus.

Beta Particle• a neutron changes into a proton &

electron.• The proton stays in the nucleus & the

electron/beta particle is propelled out of the nucleus.• Beta particle = electron

Gamma Ray• Gamma radiation has no particles.• Most dangerous type of radiation• Emitted from the nuclear bomb

Nuclear Fission• When certain elements are struck with neutrons,

the nucleus can split into smaller fragments.–Only occurs in Uranium-235 & Plutonium-239–Creates a chain reaction that releases an

immense amount of energy• ~2 lbs of U-235 creates as much energy as

20,000 tons of dynamite–Nuclear bombs use fission–Nuclear Power Plants use fission to heat water

and generate steam to produce electricity.

Nuclear Fusion• When 2 or more atoms combine to create one atom• Occurs in stars, like our sun–Hydrogen atoms fuse to make helium atoms–When stars run out of hydrogen, they start to die

• Creates more energy than fission reactions• Extremely high temperatures are needed to create

a fusion reaction–We have not been able to attain temperatures

hot enough for us to use nuclear fusion as a power source on Earth

Half-Life• Every radioactive sample decays at a certain rate• A half-life is the time required for half of the

atoms in the sample to decay into products–Half-lives can range from fractions of a second

to billions of years–Half-lives of:• Radon-222: 3.8 days• Carbon-14: 5730 years•Uranium-235: 700,000,000 years

Calculating Half-Lives

• The half-life of Carbon-14 is 5730 years. How many half-lives elapse after 17,190 years?• How many grams of C-14 is left after 3 half-

lives if it started off with 100 grams?• Starting with 80 grams, how many half-lives

have elapsed if you end with 5 grams?

halflivesofnumberhalflifeoflength

elapsedtimeofamount__

__

___

• What is the half-life of a 100 g sample of N-16 that decays to 12.5 g in 21.6 seconds?• If an 800 g sample of technetium-99 decays

to 100 g in 639,000 years, what is its half-life?• A 208 g sample of sodium-24 decays to 13 g

of sodium-24 within 60 hours. What is the half-life of this isotope?• The half-life of Au-198 is 2.7 days. How

much of a 300g sample will be left after 10.8 days?