1 Announcements & Agenda (01/19/07) You should currently be reading Ch 3 & starting Ch 4, which will be relevant to lab next week Today: More on Subatomic Particles (3.5) More on Subatomic Particles (3.5) Isotopes & Atomic Mass (3.6) Isotopes & Atomic Mass (3.6) Radiation (Ch 9 – only responsible for notes) Radiation (Ch 9 – only responsible for notes)

2 I thought the quiz was… A piece of cake. 2.Manageable. 3.Not too easy or difficult (what I expected). 4.Challenging! 5.Oh my goodness!!!

3 Last Time: Classification of Matter

4 Last Time: Know These Elements O65.0 %K 0.34 C18.0S 0.26 H10.0Na 0.14 N 3.0Cl 0.14 Ca 1.4Fe P 1.0 Zn Mg 0.50 Trace Elements As, Cr, Co, Cu, F, I, Mn, Mo, Ni, Se, Si, V

5 Methane (CH 4 ) reacts with oxygen (O 2 ) to produce carbon dioxide (CO 2 ) and water (H 2 O). COUNT THE ATOMS! SEE BOB DEMO! Last Time: Atoms Rearrange in Chemical Reactions

6 Subatomic Particles Atoms contains subatomic particles, protons have a positive (+) charge.protons have a positive (+) charge. electrons have a negative (-) charge.electrons have a negative (-) charge. like charges repel and unlike charges attract.like charges repel and unlike charges attract. neutrons are neutral.neutrons are neutral.

7 Structure of the Atom dense nucleus that contains protons and neutrons.dense nucleus that contains protons and neutrons. of electrons in a large empty space around the nucleus.of electrons in a large empty space around the nucleus.

8 Atomic Mass Scale On the atomic mass scale for subatomic particles, 1 atomic mass unit (amu) has a mass equal to 1/12 of the mass of the carbon-12 atom.1 atomic mass unit (amu) has a mass equal to 1/12 of the mass of the carbon-12 atom. a proton has a mass of about 1 (1.007) amu.a proton has a mass of about 1 (1.007) amu. a neutron has a mass of about 1 (1.008) amu.a neutron has a mass of about 1 (1.008) amu. an electron has a very small mass, amu.an electron has a very small mass, amu.

9 Summary

10 Atomic Number = The Identity of the Element Counts the number ofprotons in an atom

11 All Atoms of the Same Element Have the Same # of Protons!!! 11Na 11 protons Symbol

12

13 An atom of an element is electrically neutral; the net charge of an atom is zero.an element is electrically neutral; the net charge of an atom is zero. has an equal number of protons and electrons.has an equal number of protons and electrons. number of protons = number of electrons Aluminum has 13 protons and 13 electrons. The net charge is zero. 13 protons (13+) + 13 electrons (13 -) = 0 13 protons (13+) + 13 electrons (13 -) = 0 Electrons in An Atom

14 Mass Number Since protons and neutrons account for most of the mass of the atom, count the number of protons and neutrons to determine the mass number!!! to determine the mass number!!!

15 represents a particular atom of an element.represents a particular atom of an element. gives the mass number in the upper left corner and the atomic number in the lower left corner.gives the mass number in the upper left corner and the atomic number in the lower left corner. Example: An atom of sodium with atomic number 11 and a mass number 23 has the following atomic symbol: Example: An atom of sodium with atomic number 11 and a mass number 23 has the following atomic symbol: mass number 23 mass number 23 Na Na atomic number11 atomic number11 Nuclear Symbol

16 Subatomic Particles Example O P Zn O P Zn ? p + ? p + ? p + ? n? n? n ? e - ? e - ? e -

17 Subatomic Particles Example O P Zn O P Zn p + ? p + ? p + 8 n? n? n 8 e - ? e - ? e -

18 Subatomic Particles Example O P Zn O P Zn p + 15 p + ? p + 8 n16 n? n 8 e - 15 e - ? e -

19 Subatomic Particles Example O P Zn O P Zn p + 15 p + 30 p + 8 n16 n35 n 8 e - 15 e - 30 e -

20 Isotopes Atoms with the same number of protons, but different numbers of neutrons. Atoms with the same number of protons, but different numbers of neutrons. Atoms of the same element (same atomic number) with different mass numbers Atoms of the same element (same atomic number) with different mass numbers Isotopes of chlorine Isotopes of chlorine 35 Cl 37 Cl 1717 chlorine - 35 chlorine - 37 chlorine - 35 chlorine - 37

21 Learning Check An atom of zinc has a mass number of 65. A.Number of protons in the zinc atom A.Number of protons in the zinc atom 1) 302) 353) 65 1) 302) 353) 65 B.Number of neutrons in the zinc atom B.Number of neutrons in the zinc atom 1) 302) 353) 65 1) 302) 353) 65 C. What is the mass number of a zinc isotope with 37 neutrons? 1) 372) 653) 67 1) 372) 653) 67

22 Atomic Mass Listed on the periodic table Listed on the periodic table Gives the mass of “average” atom of each element compared to 12 C Gives the mass of “average” atom of each element compared to 12 C Average atom based on all the isotopes and their abundance % Average atom based on all the isotopes and their abundance % Atomic mass (!unlike mass #!) is not a whole # Atomic mass (!unlike mass #!) is not a whole # Na 22.99

23 Calculating Atomic Mass Percent(%) abundance of isotopes Percent(%) abundance of isotopes Mass of each isotope of that element Mass of each isotope of that element Weighted average = Weighted average = (mass isotope 1 x %) + (mass isotope 2 x %) + … (mass isotope 1 x %) + (mass isotope 2 x %) + …

24 Example: Atomic Mass of Mg Isotopes Mass of Isotope Abundance 24 Mg =24.0 amu 78.70% 25 Mg = 25.0 amu 10.13% 26 Mg = 26.0 amu 11.17% 26 Mg = 26.0 amu 11.17% Atomic mass (average mass) Mg = 24.3 amu Mg 24.3

25 Why Do We Care About Isotopes? Answer: Nuclear Stability! “belt of stability” Unstable nuclei Radioactive Radioactive Can decay to release alpha particles, beta particles and positrons. Can decay to release alpha particles, beta particles and positrons.

26 Radiation Primer: Subatomic Particles Revisited Radiation comes from nucleus of an atom Unstable nucleus emits a particle or energy protons and/or neutrons typically lost from nucleus changing identity of element protons and/or neutrons typically lost from nucleus changing identity of element  alpha (particle)  alpha (particle)  beta (particle)  beta (particle)  gamma (pure energy)  gamma (pure energy)

27 Half-Life of a Radioisotope The time for the radiation level to fall (decay) to one-half its initial value decay curve 8 mg 4 mg2 mg 1 mg 8 mg 4 mg2 mg 1 mg initial 1 half-life 2 3

28 Examples of Half-Life Isotope Half life C sec Ra days Ra days I days C years U years

29 Medical Uses of Radiation Nuclear medicine has two main arenas Diagnostic methods Diagnostic methods Small amounts of radioisotopes administered to help image an organ or follow a physiological process Small amounts of radioisotopes administered to help image an organ or follow a physiological process Therapeutic methods Therapeutic methods Larger radiation doses to deliver fatal punch to diseased tissue Larger radiation doses to deliver fatal punch to diseased tissue

30 Diagnostic Methods Radioisotopes behave chemically the same as stable isotopes of the same atom Thus, can use to target an organ or a physiological process Usually  -emitters because radiation has to emerge from the body if the imaging equipment is to see it

31 Some Radio-Imaging Isotopes P-32Eye tumors Cr-51Spleen shape and GI disorders Fe-59Bone marrow function Se-75Pancreas scan I-131Thyroid malfunction Hg-197 Kidney scan

32 PET Scans Positron Emission Tomography Good for following physiological processes Patient given short-lived  + -emitter Patient given short-lived  + -emitter The  + hits an electron in tissues The  + hits an electron in tissues C 11 6 B 5 e+e  + t 1/2 20 min

33 PET Scans With annihilation event, a pair of gamma rays are emitted in opposite directions Very clear images because signal distinguished from background radiation (only seen in one direction) e-e- 0 2  e+e

34 A PET scan instrument places patient inside a ring of detectors to see the paired, 180 o gamma rays

35 PET Scans Can incorporate C-11 into a number of organic compounds to follow Blood flow Blood flow Glucose metabolism (Fig 9E.5, Page 259) Glucose metabolism (Fig 9E.5, Page 259) Oxygen uptake Oxygen uptake Find brain areas associated with epilepsy Find hard to spot tumors

36 Abnormal lymph nodes imaged by PET scan Also:

37 Therapeutic Radiation Selective destruction of pathological cells and tissues Rapidly dividing cells most vulnerable - thus it targets cancer Used when cancer is not well localized Co-60 is common source of x-rays and  -rays

38 Therapeutic Radiation Can also deliver a radiation dose with an internal administration of selected isotopes I-131 targets thyroid cancer - thyroxine contains iodine I-131 targets thyroid cancer - thyroxine contains iodine I-125 crystals implanted in prostate gland to deliver continuous radiation (t 1/2 = 60 days) I-125 crystals implanted in prostate gland to deliver continuous radiation (t 1/2 = 60 days) Y-90 implanted in pituitary to slow tumor growth everywhere Y-90 implanted in pituitary to slow tumor growth everywhere

39 Radio-Tracer Compounds Huge use of radioisotopes to study chemical reactions Can see g/L - almost individual atoms Photosynthesis - carbon in glucose comes from CO 2 Photosynthesis - carbon in glucose comes from CO 2 Calcium - uptake is 90% efficient in children; 40% efficient in adults Calcium - uptake is 90% efficient in children; 40% efficient in adults Zinc - uptake by trees in winter 2 ft/day Zinc - uptake by trees in winter 2 ft/day