Chemistry Chapter 4: The Periodic Table

1. Chemistry Chapter 4: The Periodic Table Section 4: FromWhere Did the Elements Come?

2. Key Terms • Nuclear reaction – reaction that affects atomic nucleus • Superheavy element – an element with an atomic # > 106 • Transmutation – changing from one element to another

3. Key Terms 2 • E=mc2 – Enstein’s quantitative description of the mass energy-relationship • Here e, m and c are energy, mass & the speed of light, respectively.

4. Key Terms 3 • Supernova – explosion of stars more than 100x more massive than the sun • The blast is caused by conversion of core H & He into elements up to Fe. • During the explosion, this change yields collapse & formation of ele-ments with higher atomic # than Fe.

5. Key Terms 4 • Synthetic elements – created by chemists using particle accelerators, these elements do not occur naturally and have atomic # > 92. • Cyclotron – charged particle acceler-ator 1st invented by the American sci-entist E.O. Lawrence in 1930

6. Key Terms 5 • Synchrotron – used to create superheavy elements • This device accelerates a few types of charged particles past 1/10th the speed of light, c. • One tenth c is the top speed that cyclotrons can yield.

7. Things To Know/Answer • How do the naturally occurring elements form? • How does a transmutation change one element into another? • How are particle accelerators used to create synthetic elements?

8. Natural Elements • Only 93 of the elements in the periodic table are found in nature. • Technetium,Tc; promethium, Pm, & neptunium, Np, are found in the spectra of stars. • C, H, O, N, P & S are most of the atoms in living things.

9. Natural Elements 2 • Popular theory – common and natural elements were created in the centers of stars billions of years ago, shortly after the “Big Bang” • H & He formed after the Big Bang through cooling of temperatures.

10. Natural Elements 3 • Here, energy was able to become subatomic particles. • These formed H & He in clouds that gravity centralized. • The cloud gathering yielded great solar density which caused rising central temperature & pressure.

11. Natural Elements 4 • Nuclear reactions started in these solar centers. • Stars have fusion reactions where 4H become 1He with an apparent loss of mass that becomes energy. • E=mc2 describes this change.

12. Natural Elements 5 • Other elements can form by fusion. See Figure 28 on pg. 144. • See www.scilinks.org Origin of Elements under code HW4093.

13. Transmutations • Middle Ages = alchemists trying to turn Pb into Au via ordinary or non nuclear chemical reactions. • Were they successful? See Alchemy at code HW4006.

14. Transmutations 2 • Rutherford saw particle tracks in his experiments. • He reasoned that they came from disintegration of atomic nuclei after being struck by α-particles.

15. Transmutations 3 • W.D. Harkins, an American, & P.M.S. Blackett confirmed that Y shaped tracks meant transmutation • This was b/c N disintegrated into O and a proton when struck by an α-particle.

16. Synthetic Elements • Researchers hopped on the transmuting train & synthesized elements that were not available in nature w/ particle accelerators. • Cyclotrons & Synchrotrons use successive pulses of energy to speed up charged particles.

17. Synthetic Elements 2 • They make particles collide at high speed and energy, fuse, and form heavier elements. • Greater speed yields greater mass and more difficulty continuing acceleration

18. Synthetic Elements 3 • The charge particles must reach successive pulses on time. • If not, they slow down, lose energy and fail to fuse. • Most superheavy elements last for a small fraction of a s except for 114.

19. Synthetic Elements 4 • The only time scientists synthe-sized element 114, it lasted for 30s then decayed to 112. Why is this problematic? • Russian scientists bombarded Pu-214 with Ca-40 for 40 days to create 114.

20. Synthetic Elements 5 • Many researchers view element 114 as the beginning of a stable set of synthetic elements. Why?