1. CHAPTER 25 Nuclear Chemistry
I. The Nucleus -Terms
(p ) II
III IV

2. Ionizing Radiation
Radiation is a form of energy transferred by waves or atomic particles
Ionizing Radiation is any radiation with high enough energy to create ions (by knocking electrons out of atoms)
like UV, X, gamma, and cosmic rays
There are both natural sources of radiation (unstable nuclei and stars) and human created sources

3. Zone of Stability
Stable nuclei exist within the “zone of stability” seen on the graph…not always a 1:1 ratio of p+ to no
Outside this range, nuclei are unstable and will decay (disintegrate) into new nuclei

4. Definitions Nucleons = particles in nucleus (p+ and n0)
Nuclide refers to the nucleus of an atom
Nuclear Reactions involve transmutation where one element become another.
Radioactive Decay is the when unstable nuclei spontaneous lose energy by emitting ionizing particles; as this changes the nucleus of the atom, this also changes the type of element

5. Alpha Decay Process  Daughter Nuclide Np-237 Th-234 Ra-228
Alpha decay is a radioactive process in which a particle with two neutrons and two protons is ejected from the nucleus of a radioactive atom. The particle is identical to the nucleus of a helium atom.
Alpha decay only occurs in very heavy elements such as uranium, thorium and radium. The nuclei of these atoms are very “neutron rich” (i.e. have a lot more neutrons in their nucleus than they do protons) which makes emission of the alpha particle possible.
After an atom ejects an alpha particle, a new parent atom is formed which has two less neutrons and two less protons. Thus, when uranium-238 (which has a Z of 92) decays by alpha emission, thorium-234 is created (which has a Z of 90).
Because alpha particles contain two protons, they have a positive charge of two. Further, alpha particles are very heavy and very energetic compared to other common types of radiation. These characteristics allow alpha particles to interact readily with materials they encounter, including air, causing many ionizations in a very short distance. Typical alpha particles will travel no more than a few centimeters in air and are stopped by a sheet of paper.
Show decay on chart of nuclides,
Show smoke detector as application of alpha decay.
Parent Nuclide
Am-241
U-238
Th-232
Ra-226
Alpha Particle
(Helium Nucleus)
( amu)

6. A. Mass Defect
The mass defect describes the mass lost during the formation of nuclei
Difference between the mass of an atom and the mass of its individual particles.
amu
Mass of atom
amu
Mass of particles

7. B. Nuclear Binding Energy
Energy released when a nucleus is formed from nucleons. This contributes to the loss in mass of nucleus, described by E = mc2.
High binding energy = stable nucleus.
E = mc2
E: energy (J)
m: mass defect (kg)
c: speed of light (3.00×108 m/s)

8. B. Nuclear Binding Energy
Iron (Fe) is the most stable nucleus!!
Unstable nuclides are radioactive and undergo radioactive decay.

9. CHAPTER 25 Nuclear Chemistry
II. Radioactive Decay
(p ) II
III IV

10. Types of Spontaneous Radiation
stopped by…
Greek symbol
charge
Alpha particle ()
helium nucleus
paper 2+
Beta particle  or -
electron 1-
wood
Positron +
positron 1+
Lead or
concrete
Gamma ()
high-energy photon

11. Other Radiation particles
Greek symbol
charge
proton p+ +1
neutron n0

12. How does an electron get emitted from the nucleus?
Basically a neutron splits into a proton which stays in the nucleus and an electron is emitted ( decay) - + - + + + +
n converted to a proton and an e is emitted
n & p in nucleus
n is “really” like a p and e together

13. Transmutation Reactions
I Alpha Emission
parent
nuclide
daughter
nuclide
alpha
particle
Numbers must balance on both sides of arrow!!
238amu on left = ( amu)
92 is nucl chrg on left = on right

14. B. Nuclear Decay II Beta Emission electron III Positron Emission
*a proton 1p is not the same as a positron 0e

15. B. Nuclear Decay
IV Electron Capture
electron

16. B. Nuclear Decay Alpha capture
V Alpha Capture followed by neutron emission
Alpha capture
Gamma Emission causes no change in mass or charge and…
Usually follows the previous
types of decay.

17. Beta (Negatron) Decay Process
Daughter Nucleus
Osmium-187
Calcium-40

Antineutrino
Beta decay is a radioactive process in which an electron is emitted from the nucleus of a radioactive atom, along with an unusual particle called an antineutrino. The neutrino is an almost massless particle that carries away some of the energy from the decay process. Because this electron is from the nucleus of the atom, it is called a beta particle to distinguish it from the electrons which orbit the atom.
Like alpha decay, beta decay occurs in isotopes which are “neutron rich” (i.e. have alot more neutrons in their nucleus than they do protons). Atoms which undergo beta decay are located below the line of stable elements on the chart of the nuclides, and are typically produced in nuclear reactors.
When a nucleus ejects a beta particle, one of the neutrons in the nucleus is transformed into a proton. Since the number of protons in the nucleus has changed, a new daughter atom is formed which has one less neutron but one more proton than the parent. For example, when rhenium-187 decays (which has a Z of 75) by beta decay, osmium-187 is created (which has a Z of 76).
Beta particles have a single negative charge and weigh only a small fraction of a neutron or proton. As a result, beta particles interact less readily with material than alpha particles. Depending on the beta particles energy (which depends on the radioactive atom), beta particles will travel up to several meters in air, and are stopped by thin layers of metal or plastic.
Show compact fluorescent light bulb as application of beta decay.
Parent Nucleus
Rhenium-187
Potassium-40

Beta Particle
(electron)

18. Beta Particles Same as an electron with kinetic energy
Positive or negative charge of 1
May be positively or negatively charged
Can normally be stopped by 1 cm of plastic, wood, paper
Exception for positron emitters

19. B. Nuclear Decay Why nuclides decay…pg. 803
need stable ratio of neutrons to protons
DECAY SERIES TRANSPARENCY

20. C. Half-life Half-life (t½)
Time required for half the atoms of a radioactive nuclide to decay.
Shorter half-life = less stable.

21. C. Half-life
mf: final mass
mi: initial mass
n: # of half-lives

22. C. Half-life t½ = 5.0 s mf = mi (½)n mi = 25 g mf = (25 g)(0.5)12
Fluorine-21 has a half-life of 5.0 seconds. If you start with 25 g of fluorine-21, how many grams would remain after 60.0 s?
GIVEN:
t½ = 5.0 s
mi = 25 g
mf = ?
total time = 60.0 s
n = 60.0s ÷ 5.0s =12
WORK:
mf = mi (½)n
mf = (25 g)(0.5)12
mf = g

23. Decay Series
Many heavy elements are unstable and so they will continue to decay (be radioactive) until they finally transmute into a stable nucleus.
Here is an example of the Th-232 decay series
Thorium oxide is used to in camping lanterns to intensify the brightness when on fire.
Stable isotope