CHAPTER 22 Nuclear Chemistry

Types of Radiation Isotopes - atoms of the same element with the same number of protons but different numbers of neutrons Radioisotopes – isotope with an unstable nucleus that emits radiation to become a more stable nucleus Radioactive Decay – spontaneous reaction in which unstable nuclei lose energy in the form of nuclear particles

Nuclear Stability Why do atoms decay anyway… need stable ratio of neutrons to protons Small atoms are stable with a 1 to 1 ratio of protons to neutrons As the atomic number increases, atoms tend to have more neutrons than protons with stable ratio increasing to 1 to 1.5 The type of unbalance that is present in the nucleus determines the type of decay.

Nuclear Stability

Half-life Half-life (t½) Time required for half the atoms of a radioactive nuclide to decay. Shorter half-life = less stable. C. Johannesson

Half-life mf: final mass mi: initial mass n: # of half-lives

Half-life mf = mi (½)n mf = (25 g)(0.5)12 mf = 0.0061 g WORK: Fluorine-21 has a half-life of 5.0 seconds. If you start with 25 g of fluorine-21, how many grams would remain after 60.0 s? WORK: mf = mi (½)n mf = (25 g)(0.5)12 mf = 0.0061 g GIVEN: t½ = 5.0 s mi = 25 g mf = ? total time = 60.0 s n = 60.0s ÷ 5.0s n = 12

Types of Nuclear Particles Alpha particle (α) Composition: 2 protons, 2 neutrons Symbol: 4He or α Charge: +2 Penetrating power: low, stopped by paper or cloth

Beta particle (β) Composition: 1 electron Symbol: -1 e Charge: -1 Penetrating power: 100 times greater than alpha, stopped by wood or concrete

Gamma ray (γ ) Composition: electromagnetic waves Symbol: γ Charge: 0 Penetrating power: 1000 times greater than beta, stopped by lead or 6 feet of concrete

Types of Nuclear Decay Numbers must balance!! Alpha Emission parent nuclide daughter nuclide alpha particle Numbers must balance!!

Types of Nuclear Decay Beta Emission electron Positron Emission C. Johannesson

Types of Nuclear Decay Electron Capture electron Transmutation One element becomes another.

Fission vs. fusion

F ission splitting a nucleus into two or more smaller nuclei 1 g of 235U = 3 tons of coal

F ission chain reaction - self-propagating reaction critical mass - mass required to sustain a chain reaction

Fusion combining of two nuclei to form one nucleus of larger mass thermonuclear reaction – requires temp of 40,000,000 K to sustain 1 g of fusion fuel = 20 tons of coal occurs naturally in stars C. Johannesson

Fission vs. Fusion 235U is limited fuel is abundant danger of meltdown toxic waste thermal pollution fuel is abundant no danger of meltdown no toxic waste not yet sustainable