1. Topic: Nuclear Chemistry
Aim: What makes a nucleus stable? What are the 4 types of nuclear decay?
Do Now: What are the two subatomic particles in the nucleus?
How many p, n, & e are in an atom of K-37?
HW:

2. Nuclear Stability Remember: Unstable nuclei
Subatomic particles in the nucleus
protons & neutrons
Unstable nuclei
have too many protons
Like charges repel
Bigger atomic #, more repulsion, more instability

3. Neutron: Proton Ratio Neutrons help stabilize the nucleus
More p+ (higher atomic #) means more n are needed to stabilize the nucleus
n : p ratio close to 1:1 is MOST STABLE

4. Neutron : Proton Ratio
Larger elements tend to have larger n : p ratio (closer to 2:1)

5. Examples Determine n : p ratio of C 12 is mass # (p + n)
6 is atomic # (# of p)
Therefore, 12 – 6 = 6 neutrons
n : p ratio is 6 : 6 (or 6/6) which is 1 : 1
This isotope of carbon is stable. 12 6

6. Examples Determine the n : p ratio of Fe Is this nucleus stable?
n : p ratio is 30 : 26 (30/26) = 1.2 : 1
This nucleus is stable 56 26

7. Radioactivity & Spontaneous Nuclear Decay
Reference Tables N, O
Radioisotope – any unstable isotope that is prone to decay (radioactive)
Radioactivity - nucleus of an unstable isotope or element decays and gives off rays & particles
Transmutation - nucleus of an atom decays and ONE ELEMENT CHANGES INTO ANOTHER ELEMENT!

8. Transmutations
Natural: nucleus spontaneously decays to form a new element
Nothing needs to bombard the nucleus to change it
Table N radioisotopes all decay naturally (spontaneously)
Artificial: transforming 1 element into another by bombarding the nucleus with high-energy particles
Particle accelerators speed up the particles enough to cause an artificial transmutation
How man-made elements are produced

9. Decay Modes Each radioactive isotope has a specific decay mode.
alpha, beta, positron (all particles)
gamma (rays – energy)
How do we know which decay mode?
REFERENCE TABLE N!!!

10. Alpha Decay Alpha particle emitted by nucleus of decaying radioisotope
This is a helium nucleus,
2 protons & 2 neutrons (4-2)
Charge of +2
Symbol – Table O

11. Alpha Decay

12. Alpha Decay Example
To figure out which symbol to use for the product, see which element’s atomic # matches with your calculation!

13. Beta Decay Loss of beta particle
Has same characteristics as an electron!
Formed when a nucleus emits a neutron that converts into a proton and a beta particle
Symbol:

14. Beta Decay

15. Beta Decay Example Note: mass # does not change b/c e- have no mass!
Write the equation for beta decay of Carbon-14

16. Examples

17. Positron Decay Loss of a positron Symbol is e+ or β+
Antimatter equivalent of an electron
Same mass as electron, opposite charge
Just smile and nod. Really.
Symbol is e+ or β+

18. Positron Decay

19. Positron Decay Example
Write equation of positron decay of Neon-19.

20. Gamma Rays Loss of gamma rays Have 0 charge & 0 mass.
extremely high energy photons (light)
Have 0 charge & 0 mass.
They’re just energy!
No changes in mass or charge – just energy emitted by nucleus to help stabilize it
By-product of most nuclear decay

21. Gamma Rays

22. Separating α, β-, β+ Particles, γ Rays
Electric or magnetic fields can separate particles
Alpha particle (charge?) deflected toward ___ electrode
Beta particle (charge?) deflected toward ___ electrode
Gamma ray (charge?)… + β-
Radioactive Source γ α —

24. Sample Questions

25. Sample Questions

26. Sample Questions

27. Aug 05