1 / 24

Nuclear Chemistry

Nuclear Chemistry. Nuclear Reactions. Chemical reactions What can NOT change in a chemical reaction? Nuclear Reactions: changes that occur in the nucleus of an atom The nucleus is unstable!! Most atoms have unstable nuclei. Why are some stable, while others are not?. Primary Reason:

karenchristensen
Download Presentation

Nuclear Chemistry

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Nuclear Chemistry

  2. Nuclear Reactions • Chemical reactions • What can NOT change in a chemical reaction? • Nuclear Reactions: changes that occur in the nucleus of an atom • The nucleus is unstable!! • Most atoms have unstable nuclei.

  3. Why are some stable, while others are not? • Primary Reason: • ratio of the neutrons to the protons (n/p) • An atom is most stable when ratio is 1:1 • The maximum ratio of stability is around 1.5 : 1

  4. Radioactivity • An unstable nucleus emits rays and particles, called radiation, to become stable • The process is called radioactivity • Gain stability by LOSING energy • Discovery dealt a deathblow to Dalton’s theory of indivisible atoms

  5. Types of Radiation • Alpha particle () • helium nucleus paper 2+ • Beta particle (-) • electron 1- • Gamma () • high-energy photon lead 0

  6. 3 Radioactive Particles • 1. Alpha Particle (+) • It travels about 1/10 the speed of light (slowest) • It is the largest, most massive particle • It is the most dangerous if ingested • It has the least penetrating ability - paper can stop this particle

  7. 3 Radioactive Particles • 2. Beta Particle (-) • Fast accelerated electron • Ejected when a neutron is converted to a proton in the nucleus • Travels 1/4 the speed of light. • It is lighter and faster than the alpha particle. • Average penetrating ability - can be stopped by heavy clothing

  8. 3 Radioactive Particles • 3. Gamma Ray • Not a particle; it is high energy electromagnetic radiation • Has no mass and no charge. • Always accompanies either beta or alpha radiation. • Travels at the speed of light. • Highest penetrating ability - can be stopped by heavy shielding such as lead.

  9. Radioactive Particles Summary

  10. parent nuclide daughter nuclide alpha particle Nuclear Decay • Alpha Emission Numbers must balance!!

  11. Nuclear Decay • Beta Emission • A neutron is converted in the nucleus of an atom • A new atom is formed whose atomic number is increased by 1

  12. Nuclear Decay • Gamma Emission • Always accompanies alpha and beta emissions. • Transmutation • One element becomes another.

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

  14. So, what does this mean? • Let’s say you have 100 g of radioactive C-14. The half-life of C-14 is 5730 years. • How many grams are left after one half-life? • How many grams are left after two half-lives? 50 g 25 g

  15. Common Radioisotopes

  16. To find the remaining amount… Half-life r :final mass i :initial mass n :# of half-lives

  17. More Half-Life Equations • Total time passed (p) = n x t1/2 • To find the half-life • t1/2 = • To find the # of half lives that have passed… • n =

  18. Half-life • 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? GIVEN: t½ = 5.0 s i = 25 g r = ? p = 60.0 s n = 60.0s ÷ 5.0s =12 WORK: r = i (0.5)n r = (25 g)(0.5)12 r = 0.0061 g

  19. You try it! • If the half life element A is 3 hours and you have 90 grams of it, how many grams would be left after 9 hours?

  20. Fission • splitting a nucleus into two or more smaller nuclei • 1 g of 235U = 3 tons of coal

  21. Fission • chain reaction - self-propagating reaction

  22. 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

More Related