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Nuclear Chemistry

for Chem IB

Glen Phelps

on 2 February 2012

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Transcript of Nuclear Chemistry

Nuclear Chemistry
Chapter 10 Henri Bequerel Discovered radiation ...but he wasn't alone.... Nuclear Decay Radioactivity => Process in which an unstable atomic nucleus emits charged particles and energy. Unstable nucleus = radioactive isotope = radioisotope Radioisotopes spontaneously change into other isotopes over time. In other words, atoms of one element become atoms of a different element.
In other words, atoms of one element become atoms of a different element. 3 Types of Nuclear Decay Alpha Beta Gamma Positively charged
2 protons & 2 neutrons Is an electron released from
inside an unstable nucleus.
A neutron changes into a proton & gives away an electron. Not a particle, but energy emitted
from an unstable nucleus.
No mass, no charge. Energy waves that
travel at speed of light.
Sources of Radiation air
animals Naturally low so doesn't damage us. Cosmic radiation Sun & deep space very dangerous!!! Background Radiation... Radiation that exceeds background radiation damages cells & tissues. Nuclear radiation can ionize atoms. Within cells, bonds hold proteins & DNA molecules together. Broken by radiation.
Cells cannot function normally.
Radon-222 gas coming from decay of uranium under buildings can seep into basements. Stays in air for 3.82 days.
When breathed in, emits alpha particles. 2nd leading cause of lung cancer.
Test kits at health department.
Nuclear Radiation cannot be seen, heard or felt. Geiger counters and film badges can detect radiation. 10.2 Rates of Nuclear Decay Nuclear decay rate has to do with how fast nuclear changes takes place. All radioisotopes decay at a specific rate. Half-life=> Time required for ½ of the radioisotope to decay.
After a half-life, ½ the original amount remains. Two ½ lives……one quarter or 25% remains.
½ lives vary from fractions of a second to billions of years!
Unlike chemical reaction rates, which vary with conditions, nuclear decay rates are always the same no matter what.
Radioisotopes decay in different ways…. alpha, beta, gamma or combinations of them. Iridium-182 goes through beta decay into Osmium-182.
Ir-182 -----> Os-182 + beta particle
½ life is 15 min
After 45 minutes
what fraction is leftover? # half lives?
Radioactive dating Finding-out how old things are, carbon-14 is typically what is checked. C-14 has a ½ life of 5,730 years. It reacts with Oxygen to make carbon dioxide. Plants take-in CO2 during photosynthesis.
Animals eat plants.
After plants or animals die, C-14 no longer is ingested.
The age of any object that once lived can then be found by comparing its C-14 levels with what is already in the air or objects with a known age.
Carbon dating only works for objects that are less than 50,000 years old. More than 50,000 years, must go with other radioisotopes like K-40, U-235,
10.1 Radioactivity 10.4 Fission & Fusion Nuclear reactions involve not only
converting to different elements &
releasing pure energy.
Fission Fusion Strong force The Strong force binds protons & neutrons together in the nucleus.
Only exist inside the nucleus.
Acts then over a very, very small distance.
Size is a factor.
Small nuclei have less protons, so less Electric force.
Large nuclei have more protons, so more Electric force. Electric force increases as the nucleus gets bigger, the strong force increases…but only to a point.
In summary, the strong force does NOT increase with radius size, but the Electric force does. When a nucleus is too big, then the strong force cannot overcome the electric force. The nucleus is then ‘unstable’ or radioactive!
All nuclei with 83 or more protons are unstable.
Became referred to as fission.
ion means ‘the act of’.
fiss means to ‘split’.
E = mc2 is a very famous equation.
Really means Energy and mass are the same thing. Demonstrated in 1945 with 1st atomic bomb. 5 kg of Pu-239.
Explosion was same as 18,600 tons of TNT.
Chain reaction Critical mass=> The smallest mass needed in order to have a sustained chain reaction. Occurs inside the sun.
600 million tons/second…4 million of it into pure energy.
Tsar bomb....biggest ever Hiroshoma re-enactment fusion of hydrogen Other sources of radiation
Full transcript