Isotopes&

Radioactivity

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

Atomic Structure Review

• ATOMSATOMS– Differ by number of protons

• IONSIONS– Differ by number of electrons

• ISOTOPESISOTOPES– Differ by number of neutrons