isotopes & radioactivity
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Isotopes of Magnesium
Atomic symbol Mg Mg Mg
Number of protons 12 12 12
Number of electrons 12 12 12
Mass number 24 25 26
Number of neutronsneutrons 12 13 14
2412
2512
2612
Isotope Notation Mg-24 Mg-25 Mg-26
Timberlake, Chemistry 7th Edition, page 64
12p+
12n0
12p+
13n0
12p+
14n0
12e- 12e- 12e-
Isotopes of Hydrogen
1 p+ 1 e- 1 p+
1 n 1 e- 1 p+2 n 1 e-
Protium Deuterium Tritium
(ordinary hydrogen) (heavy hydrogen) (radioactive hydrogen)
H1
1H2
1H3
1
Ralph A. Burns, Fundamentals of Chemistry 1999, page 100
H-2 H-3H-1
Isotopes of Hydrogen
• ProtiumProtium (H-1)1 proton, 0 neutrons, 1 electronmost abundant isotope
• DeuteriumDeuterium (H-2)1 proton, 1 neutron, 1 electronused in “heavy water”
• TritiumTritium (H-3)1 proton, 2 neutrons, 1 electronradioactive
1 p+1 e-
1 p+
1 n 1 e-
1 p+2 n 1 e-
Isotopes of Three Common Elements
Element Symbol
Fractional Abundance
Average Atomic Mass
Carbon
Chlorine
Silicon
Si
Si
Si
28
29
30
27.977
28.976
29.974
92.21%
4.70%
3.09%
12 6
13 6
3517
3717
2814
2914
3014
12.01
35.45
28.09
1.11%13.00313C
98.89%12 (exactly)12C
Mass (amu)
75.53%
24.47%36.96637Cl
34.96935Cl
Mass
Number
LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World , 1996, page 110
Radioactivity (1896)1. rays or particles produced by
unstable nuclei
a. Alpha Rays – helium nucleus
b. Beta Part. – high speed electron
c. Gamma ray – high energy x-ray
2. Discovered by Becquerel –
exposed photographic film
3. Further work by CuriesAntoine-Henri Becquerel
(1852 - 1908)
Radioactivity
• One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie CurieMarie Curie (1876 - 1934).
• She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.
Radioisotopes
• Radioactive isotopes• Many uses
– Medical diagnostics– Optimal composition of fertilizers– Abrasion studies in engines and tires
Radioisotope is injected into the bloodstream toobserve circulation.
Half-Life of Isotopes
Isotope Half-Life Radiation emitted
Half-Lives and Radiation of Some Naturally Occurring Radioisotopes
Carbon-14 5.73 x 103 years
Potassium-40 1.25 x 109 years
Thorium-234 24.1 days
Radon-222 3.8 days
Radium-226 1.6 x 103 years
Thorium-230 7.54 x 104 years
Uranium-235 7.0 x 108 years
Uranium-238 4.46 x 109 years
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