NUCLEAR CHEMISTRY
I. Review:
A.
B.
C.
D.
Structure and Composition of the Nucleus
Most nuclei consist of two nucleons, protons (p) and neutrons (n.)
Isotopes have the same atomic # Z , while differing in mass #, A. (Z = # protons, A = p + n)
Nuclear properties depend upon the number of each nucleon so we must distinguish between isotopes.
In chemical reactions, atoms are rearranged to form new substances while keeping the chemical
identity of the individual atoms. Only outer electrons are involved and the release of energy is small.
E. In nuclear reactions, isotopes of one element are converted to isotopes of another element, and hence
the chemical identity of individual atoms changes. The nucleus is involved rather than outer electrons
and the release of energy is large and defined by E = mc2, where m is the change in mass and c is the
speed of light.
F. Nuclear Symbols are written as A X, X = element symbol (Ex. 238 U)
Z
92
II. Radioactivity: the spontaneous disintegration in which small particles of matter and/or ionizing
electromagnetic radiation are emitted by unstable nuclei
A. Discovery of Radioactivity and Radioactive Elements
1) Henri Becquerel: Credited with discovery of radioactivity
A)
Studied uranium compounds and their ability to fluoresce or give off visible
light after being exposed to sunlight
B)
Discovered that uranium gives off invisible rays at all times
C)
The rays penetrate the light proof cover of photographic film and expose it
2) Marie and Pierre Curie: Credited with discovery of Ra and Po
A)
Studied uranium and its ores
B)
Discovered uranium and uranium compounds are only mildly radioactive
C)
Pitchblende (a uranium ore) has four times the amount of radioactivity expected
based on its uranium content…this is due to other isotopes (Ra and Po) present
as a result of U natural radioactive decay
D)
Radium is more than a million times as radioactive as uranium and polonium is
more than five thousand times as radioactive as radium…pitchblende shields
much of this radiation from being detected which is why it is only four times
more radioactive than uranium when measured at the surface
B. Properties of Radioactive Nuclides:
1) They affect the light-sensitive emulsion on a photographic film
2) They produce an electric charge in the surrounding air
3) They produce fluorescence / phosphorescence with certain compounds
4) Their radiations have physiological effects minimized by time, distance, and shielding
5) They undergo radioactive decay (emit nuclear or ionizing radiation)
C. Nuclear Radiation: the particles and energy produced when a nucleus undergoes radioactive decay
D. Transmutation: changing the nucleus of one isotope into a different isotope or element
1) Natural radioactive decay: an unstable element decays to form a more stable nucleus
2) Artificial: man-made transmutations done in linear accelerator or nuclear reactors
E. Sources of Nuclear (or Ionizing) Radiation
1) Natural decay of radioactive elements in the ground (ex. U), in the air (ex. Rn, C-14), and in
food (K-40, C-14)
2) Natural cosmic rays from outer space (ex. Sun)
3) X-rays released by matter that has been subjected to very high electrical discharges (ex.
Hospital, dentist)
III. Nuclear Stability: Affected by the ratio of neutrons to protons
A. Stable nuclei or isotopes with low atomic numbers (Z < 20) have a neutron : proton ratio of
approximately 1 : 1. This ratio increases to approximately 1.5 : 1 as atomic number increases between
20 and 83. All nuclei beyond atomic number 83 are unstable and hence have only radioactive isotopes.
B. Nuclei with a neutron : proton ratio greater than their predicted stable ratio generally decay by beta
emission, which lowers this ratio and releases additional energy through the ejected beta particle
C. Nuclei with a neutron : proton ratio less than their predicted stable ratio generally decay by positron or
alpha emission or electron capture, which all raise this ratio and release additional energy through the
ejected positron or alpha particle or in the case of electron capture, through the emission of  rays as
electrons fall from higher levels to lower ones to fill the orbital vacated by the captured electron
D. Nuclei beyond atomic number 83 are all unstable and generally decay by a combination of Beta and
Alpha emission
IV. Nuclear Decay Types
A. Beta Decay: A high-energy, fast-moving electron is ejected from the nucleus, effectively changing a
neutron into a proton…beta particles can be deflected by like charges
 Example of Beta Emission: 14 C  14 N + 0 
6
7
1
B. Positron Decay: A high-energy, fast-moving positively-charged electron is ejected from the nucleus,
effectively changing a proton into a neutron…positrons can be deflected by like charges
1) If a positron and electron collide, the matter is transformed into energy
2) A positron is the antiparticle of an electron (equal mass, opposite charge)
3) Example of Positron Emission: 32 Cl  32 S + 0 
17
16
1
E. Electron Capture: A 1s electron is captured by the nucleus, effectively changing a proton to a neutron
 Example of Electron Capture: 40 K + 0 e  40 Ar
19
1
18
F. Alpha Decay: A high-energy, fast-moving +2 charged helium ion is ejected from the nucleus…alpha
particles can be deflected by like charges and pose the greatest health hazard (inhalation/digestion)
 Example of Alpha Emission: 238 U  234 Th + 4 
92
90
2
G. Gamma-ray Emission: Gamma radiation accompanies other types of radioactive decay
 Example of Gamma Emission: 238 U*  238 U + 0 
92
92
0
H. Neutron Decay or Capture: Neutrons can be emitted or captured by isotopes to increase their
stability…they pose the next greatest health hazard after alpha particles
1) Example of Neutron Emission: 63 Cu + 2 H  2 1 n + 63 Zn
29
1
0
30
1
1
2
2) Example of Neutron Capture: H + n 
H
1
0
1
V. Decay Properties
Decay Type
Reaction Charge Mass Change Change Relative
Penetrating Ability
Symbol
in Z
in A
Speed
0 
Beta Decay
-1
>0
+1
0
Fast
5 – 15 feet air
Paper, but not Al foil or wood
(  -)
1
Positron Decay
(  +)
Electron
Capture (e.c.)
Alpha Decay
( )
Gamma
Emission (  )
Neutron Decay
(n)
Neutron
Capture (n)
0 
1
0 e
1
4 
2
0
0
1n
0
1n
0
+1
>0
-1
0
Fast
Same as Beta Decay
-1
>0
-1
0
Fast
X rays released less than
Gamma Emission
+2
4
-2
-4
Very
Slow
2 – 8 inches in air
Not paper, skin, or clothing
0
0
0
0
Very
Fast
Several miles in air
Several ft. concrete or in. of Pb
0
1
0
-1
Slow
Several hundred feet in air
Slowed by materials w/ H
0
1
0
+1
Slow
Same as Neutron Decay
Complete the following chart
Symbol(s)
Mass Number
Charge
Relative Speed
Penetrating Ability
Alpha Particle
Beta Particle
Positron
Gamma Ray
Neutron
Proton
Electron
Complete the following nuclear reactions. Be sure to fill in any missing numbers on the given nuclear symbols
before completing the reaction.
1. 27 Al + 4 He  30 P +
13
2
15
2. 63 Cu + 2 H  2 1 n +
29
1
0
44
1
44
3.
Ca + H 
Sc +
20
1
21
4. 9 Be + 4 He  12 C +
4
2
6
31
2
32
5.
P +
H 
P +
15
1
15
6. 37 Cl +
 35 S +
17
16
7. 30 P +
 30 Si +
15
14
2
2
1
8. H +
H  H +
1
1
1
11
4
9.
B +
He  14 N +
5
2
7
63
2
10.
Cu +
H  64 Zn +
29
1
30
6
1
4
11. Li +
n  He +
3
0
2
122
1
12.
Sb +
n  123 Sb +
51
0
51
13. 214 Pb  0 e +
82
1
63
2
14.
Cu +
H  3H +
29
1
1
4 He
2
1H
1
15. 14 N +
 14 C + 1 H
7
6
1
16. 6 Li + 1 H  4 He +
3
1
2
2
3
17. H +
H  4 +
1
1
2
2
18. H +
 1H + 1 n
1
1
0
31
1
28
19.
P + H 
Si +
15
1
14
20. 14 N +
 1 H + 17 O
7
1
8
21. 239 Pu + 4 He  1 n +
94
2
0
63
1
38
22.
Cu + H 
Cl + 1 n +
29
1
17
0
63
2
64
23.
Cu +
H 
Cu +
29
1
29
24. 235 U + 2 n  95 Mo + 2 1 n +
92
1
42
0
6
2
7
25. Li +
H 
Be +
3
1
4
26. 3 H  3 He +
1
2
27. 96 Mo + 2 H  1 n +
42
1
0
98
1
28.
Mo +
n  99 Tc +
42
0
43