1. Unstable Nuclei and Radioactive Decay
Section 4.4

2. Radioactivity
Some substances spontaneously emit radiation – radioactivity
The rays and particles emitted are called “radiation”.
Radioactive elements change their identity – they can change into another element
They do this because the nuclei are unstable
Changes to atom’s nucleus is called a nuclear reaction Something else Dalton got wrong.

3. Radioactive Decay Radioactive elements emit energy as radiation
This is called ‘radioactive decay’
Unstable atoms undergo radioactive decay until they form stable atoms

4. Types of Radiation
Alpha Radiation – emitting a positively charged particle - α
Beta Radiation – emitting a negatively charged particle - β
Gamma Radiation – High energy radiation with no mass - γ

5. α Alpha Radiation Alpha radiation Made up of Alpha particles
Alpha particles have 2 protons, 2 neutrons
Alpha particles have a 2+ charge α

6. + Nuclear Equations Nuclear Equations
transmutation - an element is transformed into a new element. This can occur by natural or artificial means.
loss of an a particle
radium is emitting an a particle
                                                     +

7. Beta Radiation Beta Radiation is fast moving electrons
Attracted to positive charged items
Charge is 1-

8. Gamma Radiation High Energy radiation with no mass No charge
Usually accompany alpha and beta radiation
Account for most of the energy lost during radioactive decay

10. What Makes Nuclear Stability?
Biggest factor is neutron to proton ratio
Will be discussed in Chapter 25
Atoms with either too many or too few neutrons will be radioactive

11. Review
Explain how unstable atoms gain stability?
Atoms gain stability by losing energy as emitted radiation.
Complete the following table:
Particle
Symbol
Mass (amu)
Charge α β γ 4 2 He +2 4 -1 β
1/1840 -1 γ

12. He β γ Review α β γ Particle Symbol Mass (amu) Charge 4 +2 1/1840 -1 44 2 He -1 β γ

13. Review
Classify each as a chemical reaction, nuclear reaction, or neither
Thorium emits a beta particle:
Nuclear
Two atoms share electrons to form a bond:
Chemical
A sample of pure sulfur emits heat as it slowly cools:
Neither
A piece of iron rusts:
chemical