1. Chapter 9 pages 258-287 And Chapter 18 pages 550-553
Unit 7 Radioactivity
Chapter 9 pages
And
Chapter 18 pages

2. Structure of the Atom Protons, neutrons, electrons
Quarks- small particles that make up protons and neutrons

3. Using the periodic table
Atomic # = # of protons
The lesser of the two numbers in the element box
On periodic table, the # of protons = # of electrons

4. Atomic mass = the # of protons + # of neutrons
The greater of the two numbers in the element box
To find the # of neutrons:
Atomic mass – atomic #

5. What is the atomic number of zinc?
How many electrons does tungsten have?
How many neutrons does scandium have?
What is the atomic mass of carbon?
How many protons does astatine have?

6. Isotopes Same number of protons (it is the same element)
Therefore it has the same atomic #
Different number of neutrons
Therefore, it has a different atomic mass

7. Periodic Table Structure
Periods:
Go left to right
Increasing # of protons and electrons
Groups:
Go up and down
Have similar reactive properties

8. The Nucleus Proton and neutrons are found in the nucleus
Outside of the nucleus are the electrons
The size of the nucleus in an atom can be compared to a marble sitting in the middle of a football stadium

9. The Strong Force
The strong force holds protons and neutrons together in the nucleus
The force becomes weak the father apart the protons and neutrons are from each other
The more protons and neutrons in the nucleus, the less strongly they are held together
Ex: large atoms like Uranium

10. Radioactivity
When the strong force is not large enough to hold the nucleus together, it will decay and give off matter and energy
Again, this is most common in large atoms
Ex: 84 protons or more
Exception, smaller atoms like C-14
Elements 93 and on were created in a lab

11. Isotopes
All atoms of a certain element have the same number of protons
If an atom has a different number of neutrons than usual, it is called an isotope
These atoms are less stable and therefore radioactive
Ex: C-12 verses C-14

12. Discovering Radioactivity
Henri Becquerel discovered radioactivity in his lab in 1896 using uranium
Later, Marie and Pierre Curie discovered polonium and radium
What are the atomic numbers of these three elements?

13. Alpha Particles Alpha radiation emits an alpha particle
2 protons and 2 neutrons
It is the same as a helium nucleus
Alpha particles are the least penetrating form of radiation
Cannot pass through a sheet of paper!
Can damage cells inside your body

14. Transmutation
When an atom emits an alpha particle, it has lost two protons and therefore is not the same element
It has transmutated into a new element
Ex: Polonium (84 protons) transmutates into Lead (82 protons)

15. Beta Particles
A neutron decays into a proton and releases an electron (called a beta particle)
So a proton has been added which changes the element
Ex: Iodine (53 protons) becomes Xenon (54 protons)
CAN pass through paper and damages body cells
Stopped by aluminum foil

16. Gamma Rays
Gamma rays are a form of radiation called electromagnetic waves
They carry energy and are the most damaging
Has no mass and no charge
Only lead and concrete can stop them

17. Name Mass Charge
Alpha
Beta
Gamma

18. Half-Life
The time it takes for a half an element to decay is called its half-life
The original element is called the parent
The new element after decay is called the daughter

19. Half Life Practice Problem
The half-life of Pa-234 is 6.75 hr. How much of a sample of this isotope remains after hours?

20. Common Half-Lives Isotope Name Half-Life Hydrogen-3 12.3 years
Lead hours
Carbon ,730 years
Polonium seconds
Uranium x 10^8 years
Iodine days

21. Dating
Scientists use radioactive decay to calculate the age of rocks, fossils, etc.
Carbon-14 exists in all organic matter and can be used to date items less than 50,000 years old
Uranium-235 is often used to date rocks

22. Detecting Radioactivity
Cloud and bubble chambers are used to detect alpha or beta particle radiation
Electroscopes are used to detect electric charges
Geiger counters determine the intensity of the radiation present by the number of clicks heard

23. Background Radiation
Low level radiation is emitted by rocks, soil, and the atmosphere
It is all around us.
Sources of this radiation are radon gas decay from the earth’s crust, cosmic rays that hit the top of earth’s atmosphere, and naturally occurring radiation within your body (C-14)

24. Nuclear Fission
Nuclear fission is the process of splitting a nucleus into two smaller masses
This releases a tremendous amount of energy
An ongoing series of fission reactions is called a chain reaction

25. Critical Mass
Controlled chain reactions are needed for electricity and nuclear weapons purposes
Scientists must experiment to find the critical mass needed to keep the reaction going

26. Nuclear Fusion
Two nuclei are combined to form a new one with a larger mass
This is done when the temperature reaches millions of degrees Celsius
Ex: The sun undergoes Hydrogen fusion into Helium
The sun has enough Hydrogen to continue its fusion for another 5 billion years

27. Using Nuclear Reactions in Medicine
Scientists use tracers to follow molecules through your body to see how an organ is functioning
Ex: Patients must drink radioactive iodine to allow doctors to see how their thyroid gland (in the neck area) is functioning
Radiation can be used to stop some types of cancer cells from multiplying
Gamma rays can be used to treat tumors