Chem Chapters 12, 25 Williams

Nuclear Chemistry and Stoichiometry

Radioactivity

the emission of __ionizing__ radiation or particles caused by the spontaneous __disintegration__ of atomic __nuclei__.

* for some reason, nucleus is unstable; it "wants" to give up some energy in order to shift to a more stable configuration.

Radiation in the world

most radiation is benign, such as the type that comes from our lights. however, some are lethal (ex. too much exposure to X rays at a doctor)

Types of radiation

Alpha, Beta, Gamma, Neutron, Positron

Alpha radiation

Helium atom w/o electrons (𝛂)

* nucleus of helium atom
* common source: radium 226

Beta radiation

high energy, high speed electron (𝛃)

* common source: carbon 14

Gamma radiation

pure energy (no mass) reaching speed of light (𝛄)

* Every nuclear reaction has gamma particles associated with it but sometimes gets left out 
* common source: cobalt 60

Neutron radiation

ionizing radiation presented as free neutrons

What are electrons made up of?

Leptons

Positron radiation

a positron is a positively charged lepton (making up an electron); the anti particle of a beta particle

* behaves and looks like an electrons but has a + instead of - charge (𝛃+) 

Generation of radioactive particles (decay)

the decay of a radioactive isotope results in the production of different elements by means of different types of radiation.

Transmutation

changing one element into another element using radioactive decay, nuclear bombardment, etc.

Explain carbon dating

Carbon in a fossil is covered + preserved by dirt → fossil discovered years later, one takes a sample, measures amount of carbon 14 in sample, based upon the percentage relative to carbon 12, you can see how much of the carbon 14 decays into nitrogen → based upon how much of it has decayed, you can obtain a relative age of the fossil. 

Effect of an electric field on radiation particles

* Alpha - shielded by paper, clothing
* penetrating power **low -** 0.05 mm body tissue
* Beta - shielded by wood, metal foil
* penetrating power **moderate -** 4 mm body tissue
* Gamma - partially shielded by lead, concrete
* penetrating power **very high -** penetrates body easily

Rutherford gold foil experiment in relation to nuclear chemistry

when Rutherford shot alpha particles at the gold foil, the reason that the alpha particles passed through the gold foil is because the foil was 4-10 atoms thick and a piece of paper is approx. 40,000 atoms thick. 

Band of stability

represents the area where stable, non-radioactive isotopes exist based on their ratio of neutrons to protons.

Half life

The time it takes for half of the radioisotope to decay

* Simple half life values can be found by following the curve
* Accurate half life values can be calculated

Half life formula for calculation

mf = mi (½)(t/h) 

* mf   = final mass
* mi  = initial mass
* h = half life
* t = elapsed time

Radioisotope decay series

Some radioisotopes that will go through multiple decay steps 

* U - 238 example 
* After 13 decay steps, it finishes as Pb - 206

Fission (Transmutation) 

When a radioactive isotope splits and breaks into smaller pieces

* Natural 
* Artificial (nuclear rxns at nuclear power plants, etc)
* Work on geometric progressions (increase exponentially)
* Ex. Uranium - 235 → Neutron binds to it making it U - 236 (very unstable) → w/ energy splits into Krypton - 91 and Barium - 142

Fusion

When the temperature and pressure are extreme, small elements can be fused together to form larger elements

* Ex. 4 Hydrogen nuclei → Helium nucleus + 2 positrons - energy

Limiting Reagent

species in reaction that runs out first

* If both reagents run out at the same time, they are both the limiting reagents

Excess Reagent

reactant remaining after the limiting reagent runs out

Addition reaction

a reaction in which one __molecule__ combines with another to form a larger molecule with no other products.

Conservation of mass

the total mass of the reactants must equal the total mass of the products

Percent Yield

The ratio of the actual amount of product divided by the theoretical amount of product

* *Percent yield = (actual yield)/(theoretical yield) x 100%*

Actual yield

the amount of product that is actually collected

Theoretical yield

the amount of product that is possible of all of the limiting reagent is reacted and only produces the product