Nuclear Chemistry

Nuclear Chemistry

Radioactivity One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie (1876- 1934). She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.

Nuclear Reactions vs. Normal Chemical Changes Nuclear reactions involve the nucleus The nucleus opens, and protons and neutrons are rearranged The opening of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energy “Normal” Chemical Reactions involve electrons, not protons and neutrons

Mass Defect It is experimentally observed that the mass of an atom (containing neutrons) is always slightly less than the sum of the masses of its component particles. The difference between the atomic mass and the sum of the masses of its protons, neutrons, and electrons is called the mass defect.

Isotope Should Weigh: Does Weigh: Mass Defect: Deuterium 1.0073 + .00055 + 1.0087 = 2.01655 2.0140 0.0025 Tritium 1.0073 + .00055 + 2(1.0087) = 3.02525 3.01605 0.0092 The loss in mass is accounted for by Einstein's E = mc2, which describes conversions between matter (m) and energy (E). When the nucleus is being formed, some matter was converted into energy (called nuclear binding energy).

There are four types of nuclear reactions: Natural radioactive decay: transmutations occur by natural radioactivity Artificial transmutation: transmutations occur by nuclear disintegration caused by external stimulation as a scientist bombards a nucleus with a particle Fission: certain nuclei having a large mass are bombarded with special particles that cause the nuclei to split into two nuclei each having a smaller mass; Fusion: nuclei of light elements are combined to form heavier nuclei. The ability of a nucleus to emit a nuclear particle and energy without external stimulation The addition of another nuclear particle makes the nucleus unstable

The “Must-Know” Nuclear Particles

Penetrating Ability Gamma rays pose the greatest external risk Alpha pose the greatest risk if emitted from ingested radioactive particles

The table below contains information about nuclear reactions involving the emission of radiation. NUCLEAR CHANGES Type of Reaction Radiation (Particle) Effect on the Atomic Number Atomic Mass Alpha emission (α) 42He decrease by 2 decrease by 4 Beta emission (β) 0-1e or 0-1β increase by 1 no change Positron emission (β+) 01e or 01β decrease by 1 Gamma emission 00γ Electron capture (EC)

Nuclear reactions that involve bombardment of nuclei vary in their products. For example: 94Be + 42 He → 126C + 10n 147N + 42 He → 178O + 11H 2713Al + 11H → 2613Al + 21H 4521Sc + 10n → 4219K + 42He

Nuclear Reactions

Balancing Nuclear Reactions In the reactants (starting materials – on the left side of an equation) and products (final products – on the right side of an equation) Atomic numbers must balance and Mass numbers must balance Use a particle or isotope to fill in the missing protons and neutrons

10B + 4He 13N + 1n 5 2 7 0 nitrogen radioisotope

Write the nuclear equation for the Beta emitter Co-60. 60Co 60Ni + 0 e 27 28 -1

LC: Writing Nuclear Equations Uranium-235 is bombarded with 1 neutron in an artificial transmutation. Krypton-92 and Barium- 141 are released, as well as some neutrons. How many neutrons are released?

Practice: Examples

Technetium-99 (9943 Tc) decays by beta emission to form ruthenium-99 (9944 Ru). Phosphorus-32 decays by beta emission to form sulfur-32. ________ + 42He → 126C + 10n 42He + _________ → 24094Pu + 10n + 10n