Section 25.2 lecture for Honors & Prep chemistry

1. BELLWORK
1. What is the symbol for an alpha particle?
2. Write the nuclear equation for the alpha
decay of Uranium-238.
3. What is the symbol of a beta particle?
4. Write the nuclear equation for the beta
decay of Carbon-14.
5. Write the symbol for gamma radiation.
6. Why is gamma radiation often not included
in a nuclear equation?

2. 25.2
Lecture 25.2- Nuclear
Transformations
Radon-222 is a
radioactive isotope that
is present naturally in
the soil in some areas. It
has a constant rate of
decay. You will learn
about decay rates of
radioactive substances.

3. The nucleus is held together by the strong nuclear force
The strong nuclear force is the
strongest force known
Protons and neutrons are very close
together
They exchange a teeny bit of mass back
and forth.
When disrupted, the mass is converted
to energy according to
E=mc2
The mass is tiny.
The energy is immense.

4. Protons and neutrons experience the strong
nuclear force if close enough
Because protons repel each other the
nucleus needs a certain proton to neutron
ratio for stability

5. 25.2
More than 1,500 different nuclei are known. Of
those, only 264 are stable and do not decay or
change with time. These nuclei are in a region
called the band of stability.

6. 25.2 Nuclear Stability and Decay
The neutron-to-
proton ratio
determines the
type of decay
that occurs.

7. 25.2
A half-life (t1/2) is the time required for
one-half of the nuclei of a radioisotope
sample to decay to products.
After each half-life, half of
the existing radioactive
atoms have decayed into
atoms of a new element.

8. 25.2

9. 25.2

10. 25.2
Stable Isotope

11. 25.2
The ratio of Carbon-14 to
stable carbon in the
remains of an organism
changes in a predictable
way that enables the
archaeologist to obtain an
estimate of its age.

12. 25.1

13. 25.1

14. 25.1

15. 25.1

16. for Sample Problem 25.1

17. 25.2
The conversion of an atom of one
element to an atom of another
element is called transmutation.
Transmutation can occur by
radioactive decay.
Or
when particles bombard the
nucleus of an atom.

18. 25.2
The first artificial transmutation reaction involved
bombarding nitrogen gas with alpha particles.

19. 25.2
The elements in the periodic table with
atomic numbers above 92, the atomic
number of uranium, are called the
transuranium elements.
• All transuranium elements undergo
transmutation.
• None of the transuranium elements
occur in nature, and all of them are
radioactive.

20. 25.2
Transuranium elements are
synthesized in nuclear reactors and
nuclear accelerators.

21. 25.2 Section Quiz.
1. During nuclear decay, if the atomic number
decreases by one but the mass number is
unchanged, the radiation emitted is
a. a positron.
b. an alpha particle.
c. a neutron.
d. a proton.

22. 25.2 Section Quiz.
2. When potassium-40 (atomic number 19)
decays into calcium-40 (atomic number 20),
the process can be described as
a. positron emission.
b. alpha emission.
c. beta emission.
d. electron capture.

23. 25.2 Section Quiz.
3. If there were 128 grams of radioactive
material initially, what mass remains after four
half-lives?
a. 4 grams
b. 32 grams
c. 16 grams
d. 8 grams

24. 25.2 Section Quiz.
4. When transmutation occurs, the ________
always changes.
a. number of electrons
b. mass number
c. atomic number
d. number of neutrons

25. 25.2 Section Quiz
5. Transmutation occurs by radioactive decay
and also by
a. extreme heating.
b. chemical reaction.
c. high intensity electrical discharge.
d. particle bombardment of the nucleus.