1. The Atomic Nucleus & Radioactive Decay
Chapter 39

2. The Atom Nucleus (center of the atom) is made up of nucleons
Protons (positive charge)
Neutrons (neutral charge)
Nucleons make up almost all of the mass of the atom
Electrons (negative charge) surround the nucleus

3. Chemistry Review Atomic Number = number of protons in atom
Mass Number= number of protons + number of neutrons
Isotopes
Atoms of same element with
different numbers of neutrons

4. Question:
Since protons are positively charged, what holds them together (since positive charges repel each other)?

5. Answer: Strong Force attractive nuclear force between nucleons
Strong only when nucleons are very close to each other
why the nucleus is so small
As nucleons, get farther apart they tend to fly apart
Since the force of the repelling positive charges is greater than the strong force, neutrons are needed to separate the protons

6. Is the nucleus stable? The nucleus is not always stable
The neutron is unstable
A lone neutron will spontaneously decay into a proton and an electron

7. Chapter 39 Part 2

8. Radioactive Atoms
An atom with a nucleus that is unstable and that can spontaneously emit a particle and become the nucleus of another element
The particle is made up of protons and electrons
Remember: the number the protons determines the element (if you add or lose protons it changes the element)

9. Radioactivity
Particles decay only when their combined products have less mass after the decay than before.
Mass of a neutron > mass of an electron + proton
Energy is released
E=mc2

10. Radioactive Decay
Radioactive elements emit one of three distinct particles as they decay
Alpha
Beta
Gamma

11. Alpha Particle Made of 2 protons and 2 neutrons
Identical to nuclei of Helium

12. Alpha Decay Practice Problem
What are the products if Neptunium 238 undergoes alpha decay?

13. Beta Particle
An electron is ejected from the nucleus when a neutron is transformed into a proton

14. Beta Decay Practice Problem
What are the products if Neptunium 238 undergoes beta decay?

15. Gamma particle Massless energy Photons of electromagnetic radiation
Gamma>beta>alpha for penetrating power

16. Gamma Decay Practice Problem
What are the products if Neptunium 238 undergoes gamma decay?

17. Chapter 39 Part 3

18. Radioactive Half-Life
Radioactive Isotopes (atoms of the same element with different numbers of neutrons) decay at different rates.
Any element heavier than bismuth (atomic number 83) is radioactive

19. Radioactive Half-Life
Time needed for half of the radioactive atoms to decay
AE is the amount of substance left
A0 is the original amount of substance
t is the elapsed time
t1/2 is the half-life of the substance