nuclear reactions

1. Isotopes and Nuclear
Reactions

2. Isotopes
Na
23
11
sodium-23
Mass number
Atomic number

3. Isotopes
Isotopes: Atoms with the same number of protons,
but different numbers of neutrons.
Isotopes are atoms of the same element (same
atomic number) with different mass numbers
Isotopes of chlorine
35
Cl 37
Cl
17 17
chlorine 35 chlorine 37

4. Isotopes
Example: Carbon isotopes
12 13 14
C C C
6 6 6
98.9% 1.1% >0.1%

5. Isotopes
Atomic mass
-Listed on the periodic table
-Gives the mass of “average” atom of each element
compared to 12
C
-Average atomic mass based on all the isotopes and
their abundance %
-Atomic mass is not a whole number…it’s a weighted
average
Na
22.99

6. Isotopes
Atomic mass calculations:
Gallium is a metallic element found in small lasers
used in compact disc players. In a sample of
gallium, there is 60.2% of gallium-69 (68.9 u) atoms
and 39.8% of gallium-71 (70.9 u) atoms. What is
the atomic mass of gallium?
Mass1 x Abundance1 + Mass2 x Abundance2 = Average atomic mass
69.7u = Average atomic mass
68.9u x 60.2% + 70.9u x 39.8% = Average atomic mass

7. Isotopes
Atomic mass calculations analogy:
A chemistry student’s grade is weighted. Tests
are worth 50.%, labs are 25%, and homework is
worth 25%. A student's test average is 85.0%, lab
average is 77.0%, and homework is 91.0%.
What is the student’s average?

8. Isotopes
Atomic mass calculations:
A sample of boron consists of 10
B (mass 10.0 u) and
11
B (mass 11.0 u). If the average atomic mass of B
is 10.8 u, what is the % abundance of each boron
isotope?

9. Isotopes
A sample of boron consists of 10
B (mass 10.0 u) and 11
B (mass 11.0 u). If the average
atomic mass of B is 10.8 u, what is the % abundance of each boron isotope?
Assign X and Y values:
X = % 10
B Y = % 11
B
Determine Y in terms of X
X + Y = 1 therefore Y = 1 - X
Solve for X:
X (10.0) + (1 - X )(11.0) = 10.8
10.0X + 11.0 – 11.0X = 10.8
10.0X – 11.0X = 10.8 –11.0
- 1.0X = - 0.2
X = 0.2
X = 20%
Y = 80%
.: the % abundances of 10
B and 11
B are 20% and 80%, respectively

10. NUCLEAR REACTIONS

11. NUCLEAR REACTIONS
2
H + 3
H  4
He + 1
n1 1 2 0
nuclear fusion - joining smaller
nuclei together to form larger nuclei
produces a lot of energy
Stars produce heavier atoms from the
fusion of many hydrogen atoms.

12. NUCLEAR REACTIONS
235
U + 1
n  139
Ba + 94
Kr + 3 1
n
235
U + 1
n  146
La + 87
Br + 2 1
n
235
U + 1
n  144
Cs + 90
Rb + 2 1
n
Nuclear fission
-large nuclei are broken in to smaller
nuclei by bombardment with a low
energy neutron
-often triggers a chain reaction of
events
-large amounts of energy
released
-Also known as radioactive
decay
92
92
92
0
0
0
0
0
0
56
57
55
36
35
37

13. NUCLEAR REACTIONS
Radioactive decay
(4 types)
– alpha decay: emitting an alpha
particle (a helium nucleus)
α particle = 4
2He
– beta decay: emitting an
electron (an electron particle
from the nucleus)
β particle = 0
-1e
– gamma decay: emitting
electromagnetic radiation
Ϫ particle = 0
0 Ϫ
(another type is emitting a

14. NUCLEAR REACTIONS
Property Alpha (α) Beta (β) Gamma (Ϫ) neutron (n)
nature of
radiation
4
2
He
nucleus
0
-1
e
electron
high
energy
radiation
1
0
n
charge 2+ 1- 0 0
mass 4 u 0 0 1 u
penetrating
ability
stopped by 4
cm of air or a
sheet of paper
stopped by 12
cm of air or
several mm of
paper
intensity
decreases by
10% by 3 cm
of lead

15. NUCLEAR REACTIONS
Alpha decay

16. NUCLEAR REACTIONS
Beta decay

17. NUCLEAR REACTIONS
Beta decay

18. NUCLEAR REACTIONS
Gamma decay

19. NUCLEAR REACTIONS
Balancing Nuclear Reactions
The sums of the atomic numbers on both sides of
the equation must be equal (92 = 90 + 2)
The sums of the mass numbers on both sides of an
equation must be equal (238 = 234 + 4)
238
92U → 234
90Th + 4
2He

20. NUCLEAR REACTIONS
Write an equation for the emission of an alpha
particle from 226
88Ra
226
88Ra → 4
2He + 222
86 ___Rn

21. NUCLEAR REACTIONS
234
90Th → 234
91Pa + 0
-1e
This is possible because
1
0n → 1
1p + 0
-1e

22. Bi
Write an equation for the emission of a
beta particle from 214
82Pb
214
82Pb → 0
-1 e + 214
83 ___
NUCLEAR REACTIONS

23. Half-life - the time required for half the
concentration of an element to decompose.
Ex. If the mass of a radioisotope is 2.464 g, what
mass will remain after 6.0 h, if the half-life is 2.0 h,
and no more radioisotope is added.
mfinal = minitial (0.5)T/x x=duration of half-life
mfinal = 2.464g (0.5)6.0/2.0
= 2.464g (0.5)3.0
= 0.308g
= 0.31g
Therefore 0.31g of radioisotope remains
NUCLEAR REACTIONS

24. NUCLEAR REACTIONS
Artificial Transmutation
Alchemists never did turn lead into gold, but along the
way made many other discoveries about elements and
compounds. This was the origin of the science of
chemistry!
In artificial transmutation, a nucleus is hit by a small
nuclear particle moving at very high speed. This can
produce atoms with a desired number of protons and
neutrons.
27
13Al + 4
2He → 30
15P + 1
0n
We can now turn lead into gold!

25. NUCLEAR REACTIONS
Nuclear reactors
convert the enormous
energy released from
fission to electrical
energy.

26. NUCLEAR REACTIONS

27. NUCLEAR REACTIONS

28. NUCLEAR REACTIONS

29. NUCLEAR REACTIONS

30. NUCLEAR REACTIONS

31. NUCLEAR REACTIONS
8.9-scale earthquake threatens safety of nuclear power plants in
Japan (March 2011)
The earthquake and tsunami knocked out cooling systems
and fuel rods began overheating

32. NUCLEAR REACTIONS
Hydrogen bomb vs. Nuclear Bomb
Nuclear bomb = fission

33. NUCLEAR REACTIONS
Hydrogen bomb vs. Nuclear Bomb
Nuclear bomb = fission

34. NUCLEAR REACTIONS
Hydrogen bomb vs. Nuclear Bomb
Hydrogen bomb = fusion

35. NUCLEAR REACTIONS
Hydrogen bomb vs. Nuclear Bomb
Hydrogen bomb = fusion