Transcript CHAPTER 21
CHAPTER 21 NUCLEAR CHEMISTRY
NUCLEUS • • • NUCLEONS ARE MADE UP OF PROTONS AND NEUTRONS NUCLIDE IS AN ATOM IDENTIFIED BY THE NUMBER OF PROTONS AND NEUTRONS NUCLEAR BINDING ENERGY IS THE ENERGY RELEASED WHEN A NUCLEUS IS FORMED FROM NUCLEONS
NUCLEAR REACTIONS • CHANGES THE NUCLEUS OF A REACTION EXAMPLE
4 9
Be
+
2 4
He
12
C
6
+
0 1
n
RADIOACTIVE DECAY • SPONTANEOUS DISINTEGRATION OF A NUCLEUS INTO A SLIGHTLY LIGHTER NUCLEUS, ACCOMPANIED BY EMISSION OF PARTICLES, ELECTROMAGNETIC RADIATION OR BOTH
TYPES OF RADIOACTIVE DECAY TYPE ALPHA PARTICLE BETA PARTICLE POSITRON GAMMA RAY SYMBOL
2 4
He
1 0 1 0
CHARGE 2+ 1 1+ 0
ALPHA EMISSION • AN ALPHA PARTICLE IS TWO PROTONS AND TWO NEUTRONS BOUND TOGETHER AND IS EMITTED FROM THE NUCLEUS DURING RADIOACTIVE DECAY
EXAMPLE
210
Po
84 206
Pb
82
+
2 4
He
BETA EMISSION • A BETA PARTICLE IS AN ELECTRON EMITTED FROM THE NUCLEUS DURING RADIOACTIVE DECAY
0 1
n
EXAMPLE
1 1
p
+
1 0 14
C
6 14
N
7
+
1 0
POSITRON EMISSION • A POSITRON IS A PARTICLE THAT HAS THE SAME MASS AS AN ELECTRON, BUT HAS A POSITIVE CHARGE.
1 1
p
EXAMPLE
0 1
n
+
1 0 38
K
19 38
Ar
18
+
1 0
ELECTRON CAPTURE • AN INNER ORBITAL ELECTRON IS CAPTURED BY THE NUCLEUS OF ITS OWN ATOM
0 1
e
EXAMPLE +
1 1
p
0 1
n
106
Ag
47
+
0 1
e
106
Pd
46
GAMMA EMISSION • GAMMA RAYS ARE HIGH ENERGY ELECTROMAGNETIC WAVES EMITTED FROM A NUCLEUS AS IT CHANGES FROM THE EXCITED STATE TO A GROUND ENERGY STATE.
PRACTICE The alpha decay of iridium-174
174
Ir
77 2 4
He
170 75 Re
e
PRACTICE The beta decay of platinum-199
199
Pt
78 0 1
e
199
Au
79
e
PRACTICE Positron emission from sulfur-31
31
S
16 31 15
P
0 1
e
e
PRACTICE Krypton-76 undergoes electron capture
76
Kr
36 0 1
e
76
Br
35
HALF LIFE-t 1/2 • TIME REQUIRED FOR HALF OF THE ATOMS OF A RADIOACTIVE NUCLIDE TO DECAY
REPRESENTATIVE RADIOACTIVE NUCLIDES AND THEIR HALF-LIVES NUCLIDE HALF-LIFE
14 6
C
5715 YEARS
218 85
At
1.6 SECONDS
238
U
92
4.46 X 10 9 YEARS
239 94
Pu
2.41 X 10 4 YEARS
HALF LIFE CALCULATIONS t 1/2 =TIME ELAPSED X 1/HALF LIFE AMT REMAINING=STARTING AMT X (1/2) n WHERE n=THE NUMBER OF HALF-LIVES
EXAMPLE PHOSPHORUS-32 HAS A HALF LIFE OF 14.3 DAYS. HOW MANY MILLIGRAMS OF PHOSPHORUS-32 REMAIN AFTER 57.2 DAYS IF YOU START WITH 4.0 mg OF THE ISOTOPE?
0.25mg
PRACTICE If the half-life for the radioactive decay of zirconium-84 is 26 minutes and I start with a 175 gram sample, how much will be left over after 104 minutes?
10.9g
PRACTICE ASSUMING A HALF-LIFE OF 1599 YEARS, HOW MANY YEARS WILL BE NEEDED FOR THE DECAY OF 15/16 OF A GIVEN AMOUNT OF RADIUM-226?
6396 YEARS