You need:
Textbook
“General, Organic, & Biological Chemistry”
Smith, 2 nd edition
Online Study Ctr.: http://connect.mcgraw-hill.com/class/p_loozen_chem_105_2014
“Laboratory Manual for GOB Chem”
Timberlake, 3 rd edition
Online Syllabus & Notes access: http://learn.roguecc.edu/science/ploozen/
For exams bring:
Scantron; pencil/eraser; PT, P.S.
*

Is this really what the Alchemists were looking for?

Associated with brain-scan technology is the use of small amounts of radioactive substances.


An isotope is an atom of an element with a specific atomic number and a different mass number than another isotope of that element.
 Carbon-12 and Carbon-14 are isotopes of the same element.

Stable vs.
Unstable isotopes
 Unstable isotopes are also known as radioisotopes or radionuclides!
 Radioactivity/radioactive decay
Marie Curie, one of the pioneers in the study of radioactivity, is the first person to have been awarded two
Nobel Prizes for scientific work.
Early experiments: 1896 Becquerel


Several types of radiation can be spontaneously emitted from unstable nuclides. Ernest Rutherford discovered that naturally radioactive materials emitted three types of radiation:

Alpha
()

Beta (

)

Gamma (

)
The effect of an electromagnetic field on alpha, beta, and gamma radiation.
What can you conclude about the charge of each type?

Alpha radiation: an unstable nucleus emits a particle made of
2 p + and 2 n˚.
What atomic # change occurs for elements that emit an alpha particle?
Atom giving up alpha particle has atomic # reduced by 2
What atomic mass change occurs?
Atom giving up
 particle has atomic mass reduced by 4

a Helium nucleus)
Alpha radiation has high ionizing power , but low penetrating power
Alpha particles travel
1/10 th speed of light

Note what happens to the atomic mass and atomic # of the products that are formed

Atomic # 90 = Thorium
Atomic # 88 = radium

A beta particle is simply a high-energy electron
Travels at 9/10ths speed of light.
100x more penetrating power than alpha
The neutron also forms a proton
Atomic # increases by 1, Atomic mass is unchanged

Another type of beta radiation: positron emission has intermediate ionizing power & intermediate penetrating power.

Gamma radiation is high-energy electromagnetic radiation
Gamma radiation has no mass, does not change the element.
Often accompanied by alpha and beta emission, which do change the element's identity.
Travels at speed of light: has high penetration power!


Process whereby a radionuclide is transformed into a nuclide of another element as a result of radiation emission.

Parent nuclide --> Daughter nuclide + radiation

Nuclear equations can be written expressing this process
 Alpha decay

Beta decay
 Positron emission

Gamma decay
U-238 --> Th-234 +

Th-234 --> Pa-234 +

F-18 --> O-18 +

+
Tc-99 --> Tc-99


Decay series: many radionuclides decay in a series of steps until a stable nucleus is formed

In the U-238 decay series, each nuclide is unstable except
Pb-206.
** Radon-222 (an intermediate in this series) is the major source of natural radiation exposure for the average American.


Decay rates are measured using the concept of Half-Life.

A half -life (t
1/2
) is the time required for one-half of a given quantity of a radioactive substance to undergo decay!
After each half-life period, the quantity of material present at the beginning of the period is reduced by half.


The first sample of Es-252 discovered in
March 1952, completed its 1 st half-life by my date* of birth:)!.

*actual, not based on Kelvins:-)

Amount of radionuclide ( ) ( ) ( )
= original amount of radionuclide x
1
2 n
This calculation allows you to determine the amounts of radioactive material that has decayed, the amount that remains undecayed and the time elapsed for the decay process!
Alternative eqn:
A = A
0 e -
 t
A = Current amount of radioactivity
A
0
= Original amount of radioactivity e = base natural log (approximately 2.718)

= the decay constant = 0.693/t
1/2
(where t
1/2
= half-life) t = the amount of time elapsed from A
0 to A
Alternative alternative method: counting!:-)


The half-life of iodine-131 is
8.0 days. How much of a
0.16 g sample of iodine-131 will remain undecayed after a period of 32 days?


Strontium-90 has a half-life of 28.0 years.
How long will it take for 94% (15/16) of the strontium-90 atoms to undergo decay?