1. CHAPTER 4/25 Atomic Structure Nuclear Chemistry

2. A Long, Long Time Ago… Greek Philosophers 4 elements are Earth, Water, Fire, and Air Aristotle - first recorded atomic thoughts Matter is continuous (no atoms) Democritus (400 B.C.) - first recorded atomic theory Atoms are smallest part of matter, each type of matter has different atoms

3. A Long Time Ago… Antoine Lavoisier (1782) Used experiments in closed containers to develop the Law of Conservation of Matter Matter is neither created or destroyed in a chemical reaction Joseph Proust (1799) Analyzed water to develop the Law of Definite Proportions The elements in a compound are always in the same proportion John Dalton (1803) Compiled past research to develop the first useful atomic theory

4. John Dalton Dalton’s theory had 4 major tenets 1. All matter is composed of tiny indivisible particles called atoms. 2. Atoms of 1 element are alike, but different from those of other elements 3. Atoms combine in small, whole number ratios to form compounds 4. Chemical reactions occur when atoms are separated, joined or rearranged. However, atoms of one element cannot be changed in to atoms of another element.

5. A Little While Ago… J.J. Thomson (1897) discovers the electron using a cathode ray tube Proposes the “Plum Pudding” Model of the atom Electrons dispersed in a sphere of homogeneous positive charge.

6. Cathode Ray Tube Experiment Cathode rays attracted to the positive plate in an electric field and deflected from the negative plate.

7. The Nucleus Exists! Ernest Rutherford (1911) Uses the gold foil experiment to “discover” the nucleus

8. Results of Gold Foil Experiment… Over 98% of the particles went straight through the foil, undeflected About 2% of the particles went through but were deflected at large angles About 0.01% of the particles bounced off the gold foil About that 0.01% of particles….. …" It was quite the most incredible event that ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you." E. Rutheford

9. Rutherford’s Conclusion

10. Rutherford's Nuclear Model 1. The atom contains a tiny dense center called the nucleus the volume is about 1/10 trillionth the volume of the atom 2. The nucleus is essentially the entire mass of the atom 3. The nucleus is positively charged the amount of positive charge of the nucleus balances the negative charge of the electrons 4. The electrons move around in the empty space of the atom surrounding the nucleus Co-worker James Chadwick later adds neutrons

11. Properties of Subatomic Particles ParticleSymbolLocation Relative Electrical Charge Relative Mass Actual Mass (g) Electrone-e- Space surrounding the nucleus 1-9.11 x 10 -28 Proton p+p+ Nucleus 1+11.637 x 10 -24 Neutron n0n0 Nucleus 011.675 x 10 -24

12. Understanding Periodic Blocks Atomic Number # of protons # of electrons Element Symbol Atomic Mass The weighted average atomic mass of isotopes of an atom Mass Number #protons + # neutrons

13. Can 20.0983 Neutrons Exist??? No, 39.0983 is an weighted average mass of all natural K atoms (Takes into consideration the abundance of each isotope) All K atoms MUST have 19 protons Some have 19 neutrons, some 20, some 21… Individual isotopes are identified by their mass number (number of protons plus the number of neutrons) K-38, K-39, K-40…..

14. Identifying Protons, Neutrons, and Electrons Chlorine-35 (element-mass number) # of protons = 17 # electrons = # protons, so Chlorine -35 has 17 electrons # neutrons = mass number – protons 35-17 = 18 Why no electrons in atomic mass? Electron has a mass that is 1/1837 that of Proton or Neutron

15. Isotopes Nuclear Notation or Isotope Notation # protons = ______ # neutrons = ______ # electrons = ______ Charges and Ions – Only changes the number of electrons Finding the mass number – use symbol, p + and n o Although the periodic table does not contain the mass number of an element, the atomic mass is often reflective of the most abundant isotope of an element and can be rounded to the nearest whole number as a last resort when a mass number is not provided.

16. Atomic Mass Units The atomic masses of elements is determined by a relative scale Based on carbon-12 6 protons 6 neutrons An atomic mass unit (amu) is equal to one-twelfth of the mass of the nucleus of a carbon-12 atom

17. Atomic Mass Problems Boron has two naturally occurring isotopes: boron-10 (19.8%, 10.013 amu) and boron 11 (80.2%, 11.009 amu). What is the atomic mass of boron? Find the Abundance x Mass for each isotope and then add products together. 0.198 x 10.013 = 1.982574 0.802 x 11.009 = 8.829218 1.000 10.811792 amu Remember sig fig rules for combined calculations: In this case, identify the number of sig figs based on multiplication but keep all digits to do the addition. Look at the number of decimal places in each of the highlighted values and round to the least number of decimal places following addition.

18. Period GroupGroup Organization of the Periodic Table There are 18 groups and 7 periods in the periodic table

19. Chemical vs. Nuclear Change Chemical Change- produces new kinds of matter with new properties Involves breaking and forming BONDS Accomplished by rearrangement of ELECTRONS Nuclear Change- produces a new nucleus that contains less energy Involves emission or capture of nuclear particles Accomplished by changing the number of PROTONS and NEUTRONS in nucleus

20. Characteristics of the Various Types of Radiation AlphaBetaGamma Symbol Shielding Easy (skin, clothes, paper) Medium (aluminum foil) Difficult (lead, concrete) EnergyHighMediumLow Biological HazardHighMediumLow-Medium Actual HazardLowMediumHigh

21. Ionizing vs. Non-ionizing Radiation Ionizing Radiation- has significant energy to change atoms and molecules into ions Types: alpha, beta, gamma, x-rays Effects to living organisms: changes in, DNA (cell death/cancer) Nonionizing radiation- does not have significant energy to ionize atoms or molecules (types: microwaves, visible light, radiowaves)

22. Nuclear Stability (Nuclear Force vs. Electrostatic Force ) Nuclear force arises between protons and neutrons due to their close proximity to one another (attractive force) Electrostatic force arises from the interaction between two protons (repulsive force)

23. Neutron to Proton Ration and the Band of Stability As the atomic number increases, more and more neutrons are needed to create a strong nuclear force to oppose and increasing electrostatic force 1:1 1.5:1

24. Nuclear Reactions

25. Nuclear Decay

26. Neutron/Proton Ratios- Alpha and Beta Decay 1:1 1.5:1

27. Neutron/Proton Ratios- Positron Emission and Electron Capture 1:1 1.5:1

28. Radioactive Decay Half-lives Half-life is the time taken for half of the atoms of a radio-active substance to decay. Number of half-lives TE/t 1/2 5 variables to consider 1.Initial quantity 2.Final quantity 3.# of half-lives = n 4.Value of a half life = t 1/2 5.Time Elapsed = TE

29. Sample Problem A sample of radioactive iridium has a half life of 12 years. In 60 years, how much iridium would remain from a 50g sample? Initial= Final= Time Elapsed= # of half lives= Value of 1 half life= 50g 12 years 60 years ? 60/12 = 5

30. Half-life Half-lives can range from a millionth of a second to millions of years The wide range of half- lives can be attributed to the intitial stability of the isotope, its mass and the number of decays it must undergo to become stable

31. Carbon Dating Carbon, predominantly carbon-12, is a major constituent of all living things Radioactive carbon-14 produced in our upper atmosphere combines with oxygen to form carbon dioxide and is incorporated into the cycle of all living things. Throughout an organisms lifetime, the ratio of carbon-12 and carbon-14 remains constant. When an organism dies, it no longer takes in carbon-14 and therefore the ratio of carbon-12 to carbon-14 changes The half-life of carbon 14 is 5370 Carbon dating is useful for determining the age of fossils that are less than 60,000 yrs. old

32. Transmutation All nuclear reactions are: transmutation reactions o Some transmutation reactions are induced o All transuranium elements (atomic #93 and greater) have been produced through induced transmutation. Transmutation Conversion of an element into an atom of another element

33. Writing Induced Transmutation Reactions Write the balanced nuclear equation for the induced transmutation of aluminum-27 into sodium-24 by neutron bombardment. An alpha particle is released in the reaction. Write the balanced nuclear equation for the alpha particle bombardment of Pu-239. One of the reaction products is a neutron.

34. Nuclear Reactions for Energy Fission- nucleus broken into 2 smaller nuclei Fusion- smaller nuclei join to form a larger, more stable nuclei

35. Reactants and Products

36. Nuclear Power- generated by a controlled fission chain reaction Control rods- absorb neutrons to slow the chain reaction Made of cadmium Inserted or withdrawn to keep temp of reaction steady Moderators- slow neutrons down so they DO hit uranium fuel rods Made of water, beryllium, or graphite Intended to allow neutrons to be absorbed by uranium

37. Cooling and Shielding Water- acts as a coolant and transfers heat between reactor and turbines that produce electricity Steel & concrete- surround core and protect personnel by absorbing radiation

38. Diagram of a Nuclear Fission Reactor