1. Physics Chapter 33 and 34

2. Starter 3/8 and 3/9
What did we learn about the atom from Millikan’s oil drop experiment?
Every element has (the same/different) atomic spectrum. An atomic spectrum is (continuous/discontinuous)

3. The Nucleus of an atom contains
Protons- positively charged
Neutrons- no charge

4. Isotopes Atoms of the same element can have different atomic masses
An element is defined by the number of protons in its nucleus
Therefore, the difference in mass is due to the number of neutrons in the nucleus
Atoms with the same number of protons but differing number of neutrons are known as isotopes
All isotopes of the same element have the same chemical properties

5. Nuclear Symbol
An element symbol that includes both the atomic number and mass number

6. Example 1
Carbon has three isotopes: Carbon 12, 13, and 14. Each one has 6 protons but….
Carbon-12 has ______ neutrons
Carbon-13 has ______ neutrons
Carbon 14 has ______ neutrons.

7. Example 2
Hydrogen has three isotopes: Hydrogen 1, 2 and 3. Hydrogen 2 is called deuterium and hydrogen 3 is called tritium. (Write the element symbol for each below)

8. Radioactive Decay
Heavier nuclei are unstable due to large number of positively charged protons packed closely together within the nucleus
These HEAVIER elements are unstable and emit particles until they become stable

9. 3 Types of Decay –Alpha Decay
The nucleus emits a helium nucleus
Symbol: He or α Overall Charge: +2
• an alpha particle is made of 2 protons and 2 neutrons
• the original nucleus is called the parent nucleus
• the resulting nucleus is called the daughter nucleus
• Alpha Decay

10. Nuclear Equations Now try two on your own:
Alpha decay of americium-24 _______________________________________________________
Alpha decay of radium-226 _______________________________________________________

11. Beta Decay The nucleus emits an electron/beta particle
Symbol: β or 𝟎 −𝟏 e Overall Charge -1
In the nucleus, a neutron transmutes into both a proton and an electron
n  p+1 + e-1

12. Beta Decay cont.
How does this affect the atomic number and mass number?
The atomic number goes up by one
The mass number stays the same

13. Nuclear Equations Now try two on your own:
Beta decay of cesium ______________________________________________________
Beta decay of xenon _______________________________________________________

14. Gamma Decay The nucleus emits a high energy wave or gamma particle
Symbol: γ and Overall Charge: 0
No particle lost
After emission of an alpha or beta particle, the nucleus has surplus energy. This is shown with a *
When the excited atom relaxes it releases the excess energy in the form of light, and returns to a lower, more stable energy state.

15. Beta Decay followed by Gamma Decay

16. Nuclear Equations Now try two on your own:
Beta decay of boron-12 followed by gamma decay
________________________________________________________
Alpha decay of uranium-238 followed by gamma decay

17. Starter 3/10 and 3/13
Neptunium has 93 protons, one isotope has 147 neutrons.
1. Write the nuclear symbol for Neptunium
2. This isotope goes through alpha decay, write the nuclear equation for this process.
Element 91 Pa, 92 U, 93 Np, 94 Pu, 95 Am

18. Radiation and You
Radioactivity has been around longer than humans have
It is as much a part of our environment as the sun and the rain.
It is what warms the interior of Earth and makes it molten.
Radioactive decay inside Earth heats the water that spurts from a geyser or that wells up from a natural hot spring.
Even the helium in a child’s balloon is the result of radioactivity. Its nuclei are nothing more than alpha particles that were once shot out of radioactive nuclei

19. Radiation and You
Sources of natural radiation include cosmic rays, Earth minerals, and radon in the air.
Radiation is in the ground you stand on, and in the bricks and stones of surrounding buildings.
Even the cleanest air we breathe is slightly radioactive.
If our bodies could not tolerate this natural background radiation, we wouldn’t be here.

20. The pie chart shows origins of radiation exposure for an average individual in the United States.

21. Units of Radiation
Radiation dosage is commonly measured in rads (radiation absorbed dose)
One rad is equal to 0.01 joule of radiant energy absorbed per kilogram of tissue
Rad does not necessarily measure potential damage
To measure radiation dosage based on potential damage with use the rem (roentgen equivalent man)
Rem takes into account the type of radiation and the amount
Particle
Radiation Dosage
Factor
Health Effect
Alpha
1 rad 1
1 rems
Beta 10
10 rem

22. Radioactive Half Life
By definition, the amount of radioactive material that decays to another material is determined by its half life.
A half life is the amount of time required for ½ of the sample to decay.
The equation for a half life is:
Where a0 is the amount you start with and a is the amount you have left after x half lives.
Half-life is different for different isotopes – some decay quickly and some very s l o w l y

23. Half-Lives can vary GREATLY
Radon – 222 has a half-life of about 3 days, while Radon 216 has a half-life of 4.5 X seconds.
Uranium-235 has a half life of 700 million years

24. All decaying elements follow the shape shown below.

25. Thallium 201 can be injected into a person’s blood stream to see if there is adequate blood flow in all vessels.
What is the half-life of Thallium- 201?

26. Number of Half Lives 1 2 3 4 5
Percent Remaining

27. Radiometric Dating
Using the length of the half-life to determine age of an object. (Elements are trapped)
Cesium-124 has a half-life of 31 seconds. A sample of Cesium – 124 in a laboratory has an initial mass of 40mg.
Calculate the amount of time it will take for the sample to decay to 5mg.  
Calculate how much Cesium – 124 will remain after 124 s (2 min 4 seconds).

28. Half Life Problems
Pd-100 has a half-life of 3.6 days. If one had 985 atoms at the start, how many atoms would be present after days?

29. Side note: Carbon dating can be used to date things that were once living – the half-life of Carbon-14 is 5730 years.
Uranium-235 and 238 have been used to date rocks because they have really long half-lives.