Download Presentation
## Nuclear Chemistry

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -

**Nuclear Chemistry**Bravo – 15,000 kilotons**Nuclear Symbols**Mass number (p+ + no) Element symbol Atomic number (number of p+)**Types of Radioactive Decay**2+ • alpha production (a): helium nucleus • beta production (b): neutron splits into an electron and a proton**CREATING A REACTION (α-particle)**• On either side of the arrow, the mass number and atomic number MUST be the same (alpha-particle is always a helium nucleus) 238U 4He + 234Th 92 2 90 • On the left side, mass number is 238 • On the right side, 234 + 4 = 238 • On the left side, the atomic number is 92 • On the right side, 90 +2 = 92**CREATING A REACTION (β-particle)**• Both sides of the reaction still need to balance. • In beta-radiation, a neutron splits apart to form an electron and a proton 234Th + 234Pa 0e 90 91 -1 • On the left side, mass number is 234 • On the right side, 234 + 0 = 234 • On the left side, the atomic number is 90 • On the right side, 91 - 1 = 90**Alpha Radiation**Limited to VERY large nucleii.**Beta Radiation**Converts a neutron into a proton.**PRACTICE**• Each of the following compounds emits an alpha particle, write the balanced nuclear reaction • 222Ra 88 • 208Po 84**PRACTICE**• Each of the following compounds emits a beta particle, write the balanced nuclear reaction • 14C 6 • 131I 53**Types of Radioactive Decay**• gamma ray production (g): • positron production: • electron capture: (inner-orbital electron is captured by the nucleus)**GAMMA RADIATION**• Gamma radiation does not produce any particles by itself • It is tied to another radioactive decay • Because the release of radioactive particles “frees” some energy in the nucleus, this energy takes the form of gamma radiation • There is a lot of energy holding the nucleus together so gamma radiation has a LOT of energy**Positron and Electron capture**• Positron emissions occur when a proton splits apart into a neutron and an electron • Therefore the mass number does not change, but the atomic number changes the element into something new • Electron capture occurs when a proton “captures” one of the inner valence electrons and converts it into a neutron • This causes the release of a powerful neutrino (as powerful as gamma radiation)**TRY THESE**• The following go through a positron emission. Write the balanced reaction: • 17F 9 • 31S 16**TRY THESE**• The following go through an electron capture. Write a balanced equation. • 76Kr 36 • 125I 53**ANOTHER WAY TO SYMBOLIZE ISOTOPES**• So far we have seen one way to symbolize isotopes: • 17F 9 • 31S 16 • Since we know the number of protons, we can symbolize the isotope with just the mass number: • Fluorine-17 • Sulphur-31**Deflection of Decay Particles**attract Opposite charges_________ each other. repel Like charges_________ each other.**NuclearStability**Decay will occur in such a way as to return a nucleus to the band (line) of stability.**HALF LIFE**• When an isotope goes through a radioactive emission, it does so at a fairly constant rate • Scientists use this property to date items • Half-life: The time it takes for ½ of a radioactive isotope to decay to a stable form • Example: Carbon-14 has a half life of 5730 years • It takes 5730 years for ½ of radioactive Carbon-14 to decay to the stable form or Nitrogen-14 • 14C 0e + 14N 6 -1 7**HOW TO SOLVE HALF-LIFE**• Iodine-131 is used to destroy thyroid tissue in an over-productive thyroid gland. The half-life of iodine-131 is 8 days. If a hospital received a shipment of 200g of iodine-131, how much iodine-131 would remain after 32 days?**SOLUTION**• Step 1: Find out how many ½-lives have occurred • (32 days/8 days for half-lives) • 4 half-lives • Step 2: Four each half-life, divide the sample by 2 • 4 half lives = ½ x ½ x ½ x ½ = 1/16 • Step 3: Divide the initial sample size • 200g/16 = 12.5g will remain**TRY THIS**• Mercury-197 is used for kidney scans and has a half-life of 3 days. If the 32g of mercury-197 is ordered, but takes 15 days to arrive, how much would arrive with the shipment?**A radioactive nucleus reaches a stable state by a series of**steps A Decay Series**Nuclear Fission and Fusion**• Fusion:Combining two light nuclei to form a heavier, more stable nucleus. • Fission: Splitting a heavy nucleus into two nuclei with smaller mass numbers.**Energy and Mass**Nuclear changes occur with small but measurable losses of mass. The lost mass is called the mass defect, and is converted to energy according to Einstein’s equation: DE = Dmc2 Dm = mass defect DE = change in energy c = speed of light Because c2 is so large, even small amounts of mass are converted to enormous amount of energy.**Fission Processes**A self-sustaining fission process is called a chain reaction.**MORE PRACTICE PROBLEMS**• Nitrogen-13 emits beta radiation and decays to Carbon-13. This has a half-life of 10 minutes. You start with 2.0g of Nitrogen-13: • Write out the balanced nuclear reaction. • Calculate how much nitrogen-13 is remaining after 40 minutes.**MORE PRACTICE PROBLEMS**• Manganese-56 decays with beta radiation and has a half-life of 2.6 hours. You begin with 1mg of Manganese-56: • Write the balanced nuclear reaction. • How much manganese-56 is left after 10.4 hours?