Nuclear Chemistry

1. Nuclear Chemistry

2. “regular” chemistry involves only the ELECTRONS in atoms All the rest of this year we will be studying only “regular” chemistry

3. “nuclear” chemistry involves only the NUCLEUS in atoms In this chapter (and only this chapter) we will be studying “nuclear” chemistry

4. Important Reminder! • Every atom of the same element must have the same number of PROTONS in its nucleus • For example, for Lithium to be Lithium, it must have 3 protons. An element with only two protons would be He, with 4 protons Be • If the number of protons in a nucleus changes, the atom becomes a different element!

5. Remember the alchemists? • They wanted to change Pb (82 protons) into Au (79 protons) • To achieve this would have meant removing 3 protons from the Pb atom’s nucleus • Alchemists would have needed to do NUCLEAR chemistry

6. Stability of atoms • All the atoms we have studied so far have been “stable”. That means they stay the same and don’t change into other atoms • Some atoms are notstable. They tend to “decay” into other atoms. • Unstable atoms are called RADIOISOPTOPES

7. Which atoms are unstable? • The ratio of protons and neutrons in the nucleus determines an atom stability Stable atoms # of n = # of p (1 to 1 ratio) All atoms with more than 83 protons are unstable

8. Which atoms are unstable? • All atoms with more than 83 protons • Some isotopes of atoms with less than 83 protons do not have the right proton to neutron ratio to be stable Remember! An isotope is an atom with more or less neutrons than other atoms of that same element

9. What happens when an unstable atom “decays” ? • It emits (gives off) radiation particles. This means it is radioactive. • It makes a new atom that is more stable

10. Types of Radiation particles • Alpha • Beta • Positron • Gamma Ray

11. Alpha Particles αGreek letter alpha It is the nucleus of a He atom (no e-) with 2 protons, 2 neutrons and a charge of +2 He 4 2

12. Beta Particles - β or βGreek letter beta Like an electron except it comes out of the nucleus, not the e- cloud has negligible (no) mass has a charge of -1

13. Positron Particles + βGreek letter beta has negligible (no) mass has a charge of +1 Like an e- (or β) but with a positive charge

14. Gamma Rays γ Greek letter gamma High energy particle, like x-rays no mass no charge

15. Penetrating power

18. When an unstable atom undergoes alpha decay….. radiation Parent atom Daughter product + He Th U 4 2 231 90 235 92 decays to Thorium-231 and an alpha particle Uranium-235

19. What is happening here? + He At Fr 4 2 216 85 220 87

20. What is happening here? + He At Fr 4 2 216 85 220 87 Fr-220 decays to At-216 and an alpha particle

21. Ra -226 Rn- 222 Th-232 Look in Table N to find other atoms whose decay mode is also an alpha particle The following unstable atoms decay by emitting an alpha particle

22. Write the decay equation for: Ra -226 Step 1: Re-write the atom symbol so it includes both atomic mass and atomic number (look it up!) Ra 226 88 Atomic mass Atomic number

23. Write the decay equation for Ra-226: Step 2: Put the unstable atom on the left side of the decay arrow Ra 226 88 Radium -226 decays to

24. Write the decay equation for Ra-226: Step 3: Look up decay mode for the atom in Table N and write that after the decay arrow α Ra 226 88 4 2 Radium -226 decays to alpha particle

25. Write the decay equation for Ra-226: Step 4: Find the daughter product by conserving mass and charge 226 = 4 + 222 α Ra X 226 88 4 2 222 86 + 88 = 2 + 86 Radium -226 decays to alpha and atom X particle

26. Write the decay equation for Ra-226: Step 5: Identify the daughter product by looking up its atomic number in the periodic table α Ra Rn 226 88 4 2 222 86 + Radium -226 decays to alpha and Radon-222 particle

27. You try it for: Radon -222 Thorium – 232 Uranium - 233