1. RADIATION!!!

2. 7.1 – Atomic Theory and Radioactive Decay
Natural background radiation exists all around us.
This radiation consists of high energy particles or waves being emitted from a variety of materials.
Like the sun, radio stations, electronic devices, TV’s, cell phones, lights, etc...
Being exposed to radioactive materials can be beneficial or harmful

3. Beneficial (good) radiation exposure
X-rays and light!
Radiation therapy (cancer treatment)
Electricity generation (nuclear power plants)

4. Harmful (bad) radiation exposure
Too much of any radiation...
Can cause Cancer
Skin cancer from sun (UV) radiation
Body cancer from high amounts of radiation
Can cause genetic mutations
Radiation affects and mutates the DNA in our body cells and then causes mutations in offspring

5. WHAT IS RADIATION??
Radioactivity (radiation) is the release of high energy particles or waves
When atoms lose high energy particles and waves, ions or even new atoms can be formed
High energy waves and particles are called ‘radiation’ when they leave the atom

6. The Electromagnetic Spectrum
The higher the frequency of radiation
(ie. the shorter the wavelength) = The more harmful the radiation is for you!

7. Radium salts (a radioactive
element), after being placed
on a photographic plate,
leave behind the dark traces
of radiation

8. Searching for Invisible Rays
Radiation is everywhere, but can be difficult to detect
Roentgen named X-rays with an “X” 100 years ago because they were previously unknown
Becquerel realized uranium emitted seemingly invisible energy as well
Marie Curie and her husband Pierre named this energy radioactivity
Early discoveries of radiation relied on photographic equipment
Later, more sophisticated devices such as the Geiger counter were developed to more precisely measure radioactivity

9. Isotopes and Mass Number
Isotopes are different atoms of the same element, with the difference between the two atoms being the number of neutrons in the nucleus.
Isotopes have the same number of protons and therefore the same atomic number as each other.
By having different numbers of neutrons, isotopes have different mass numbers.
Atomic mass = proportional average of the mass numbers for all isotopes of an element.
19.9% of boron atoms have 5 neutrons, 80.1% have 6 neutrons
19.9% have a mass number of 10, and 80.1% have a mass number of 11
(.199 * 10) + (.801*11) = 10.8 = atomic mass of boron

10. Representing Isotopes
Isotopes are written using standard atomic notation.
Chemical symbol + atomic number + mass number.
Potassium has three isotopes
Potassium is found in nature in a certain ratio of isotopes.
93.2% is potassium-39, 1.0% is potassium-40, and 6.7% is potassium-41
Atomic mass = (0.932 x 39) + (0.001 x 40) + (0.067 x 41) = 39.1

11. Radioactive Decay
Unlike all previously discovered chemical reactions, radioactivity sometimes resulted in the formation of completely new atoms.
Radioactivity results from an atom having an unstable nucleus
When these nuclei lose energy and break apart, decay occurs
Radioactive decay releases energy from the nucleus as radiation
Radioactive atoms release energy until they become stable, often ending up as different atoms
For examle: uranium-238 decays in several stages until it finally becomes lead-206
An element may have only certain isotopes that are radioactive. These are called radioisotopes

12. Radioactive Decay

13. Three Types of Radiation
When atoms are unstable, they break apart to become new, more stable atoms and release radiation... There are 3 types that can be released.
Positive alpha radiation α
Negative beta radiation β
Neutral gamma radiation γ

14. Alpha (α) radiation Alpha radiation is a stream of alpha particles
These particles are the same as a helium nucleus so we represent α radiation as:
Because it has two protons, it has a charge of 2+
The release of alpha particles is called alpha decay
Alpha particles are slow and penetrate materials much less than the other forms of radiation.
A sheet of paper will stop an alpha particle

15. ** Notice – the product side atomic masses add up to the reactant side (as well as the atomic numbers)
You try: Ac  Fr He
Decays to +
____
____
221 89

16. Beta (β) Radiation (Beta decay)
Beta radiation is a stream of beta particles
Beta particles are the same as an electron. So we represent radiation as:
Beta decay occurs when a neutron changes into a proton + an electron. The proton stays in the nucleus and the electron is released.
Beta particles are faster than alpha particles. A sheet of aluminum foil will stop a beta particle.

17. ** Notice – the product side atomic masses add up to the reactant side (as well as the atomic numbers)
You try: Hg  Tl β
Decays to + O -1
___
____
201 81

18. Gamma (γ) Radiation
Gamma radiation is a ray of high energy, short-wavelength radiation
no charge and no mass
the highest energy form of electromagnetic radiation
results from energy being released from a high-energy nucleus. It is shown by:
It takes thick blocks of lead or concrete to stop gamma rays
Sometimes reactions can release more than 1 type of radiation.
For example: Uranium-238 decays into an alpha particle and also releases gamma rays

19. Gamma Radiation
Uranium is releasing an Alpha particle and Gamma Radiation
Nickel is decaying and giving off just Gamma Radiation
Notice – no change in atomic mass or number!

22. Try some radioactive decay questions...
Pa  Ac + ___ C  ___ + β U  Cs + ____ + γ
227
____
____
α / He 89 14
____
____ N 7 Sr 92
____
____ 37

23. Video...
– A is for Atom (part I)
– A is for Atom (part II)
– Nuclear Decay Song

24. Assignment Practice problems on Pg 295 & 296 of text
Reading Check Pg 296
Check Your Understanding Pg 301 of text
Only questions 11, 12, 13 a,b,c