Nuclear Chemistry THE NUCLEAR ATOM

Radioactivity Not all atoms are stable. Unstable atoms break down and give off energy to become more stable. These atoms are referred to as RADIOISOTOPES. The energy and particles that are given off when radioisotopes break down are called RADIATION. Radioisotopes break down in a series of nuclear reactions known as NUCLEAR DECAY.

Nuclear Decay 3 Types of Radiation Alpha Beta Gamma Type of radiation emitted is determined by the neutron to proton ratio. Stable nuclei have a ratio that is found within the BAND OF STABILITY. (see graph p. 803) Small atoms have a ratio of approx. 1 Heavy atoms have a ratio of approx. 1.5

Alpha Radiation Alpha Decay occurs when the nucleus is too big. In alpha decay, an alpha particle or helium nucleus is emitted. ( 4 2 He) 2 protons 2 neutrons 0 electrons Ra  Rn He

Beta Radiation Beta Decay occurs when there are too many neutrons relative to protons. In beta decay, a neutron turns into a proton by giving off a beta particle or electron. ( 0 -1 e) n 0  p + + e Cu  Zn e

Gamma Radiation Gamma radiation or gamma rays are given off during alpha or beta decay. Gamma rays have no mass and no charge. ( γ ) Therefore, they do not alter the number of protons or neutrons in the nucleus Ra  Rn He + γ

Decay Equations Practice… Write the decay equation. Uranium-238 undergoes α decay. Bismuth-210 undergoes β decay. Thorium-230 undergoes α and γ decay. Lead-214 undergoes β and γ decay.

Nuclear Equation Practice Cu + 2 H → 2 1 n + ____ Ca + 1 H → 44 Sc + ____ 3. 9 Be + 4 He → 12 C + ____ P + 2 H → 32 P + ____ Cl + ____ → 35 S + 4 He 6. ____ → 237 Np + α Pb → β + ____

Damage from Radiation Alpha, beta, and gamma can ALL cause damage. However, they differ in the degree and how easily you are protected.

Half-Life: rate of decay All radioactive decay occurs at a steady rate. The rate is measured in terms of how long it takes for ½ of the substance to decay. (half-life) Each substance has its own half-life. Carbon x 10 3 years Radon days Helium seconds

Half-Life Problems What is the half life of the graphed material? What mass of radioisotope will remain after 9.0 hours? How long will it take for only ¾ of the radioisotope to decay? How long for only grams to remain?

Half Life Practice 1. Initial mass = 64g4 half livesFinal mass = ? 2. Initial mass = 32gt = 8.0yr½ life = 2.0yr Final mass = ? 3. Initial mass = 128gt = 5d½ life = 24hr Final mass = ? 4. Initial mass = 400.0gFinal mass = 50.0g ½ life = 13.6dt = ? 5. Initial mass = gFinal mass = g ½ life = 2325yrt=?

Other Radioactive Reactions Fission and Fusion Fission is the SPLITTING of atoms. …what happens in a nuclear reactor Fusion is the COMBINING of atoms. …what happens on the sun Both result in the release of large amounts of energy.

Fission Fission occurs when certain nuclei are bombarded with neutrons. When the atom splits, it releases additional neutrons which cause other atoms to split creating a chain reaction.

Fusion Fusion occurs when small nuclei combine to create larger nuclei. Fusion creates MORE energy than fission. Neutrons, positrons, or electrons may be given off in a fusion reaction. Deuterium ( 2 H) + Tritium( 3 H)  Helium ( 4 He) + neutron ( 1 n)

Pros and Cons Fission Pro - relatively easy to control Con - produce radioactive wastes Fusion Pro - produce little radioactive wastes Con - difficult to initiate and control

Uses of Radioactivity ???