1. ATOMS & ISOTOPES Mrs. Page Chemistry10 Parts of presentation modified from a PowerPoint presentation prepared by J. Crelling, Southern Illinois University

2. LEARNING OBJECTIVES You will be able to define what an isotope is. You will be able to determine the number of protons, neutrons, and electrons in different isotopes of the same element. You will understand that atomic mass You will understand what radioactivity is the average of the naturally occurring isotopes of an element. You will be able to give examples of how radioisotopes are used in industry and medicine.

3. ATOMS  Contain protons, neutrons, and electrons  Protons & neutrons are found in the nucleus  The nucleus contains most of the mass of an atom  Electrons are distributed around the nucleus in energy levels/shells/orbitals (which make up the electron cloud)  The outermost electrons in the shell farthest from the nucleus are called valence electrons http://www.universetoday.com/

4. ELECTRONS  First subatomic particle discovered  1897 J.J. Thomson used the cathode ray tube to discover the electron  Has a negative charge (-1)  Mass = 9.110 x 10 -28 g (0.0005 amu)  Electrons are located in energy levels which make up the electron cloud  Electrons in the outermost energy level are called valence electrons  Valence electrons are responsible the for the reactivity of an atom.

5. PROTON  Observed by E. Goldstein in 1896  Rutherford is given credit for showing that atoms contain both negatively and positively charged particles (gold foil experiment)  Has a charge of +1  Relative Mass of 1 AMU (1.673 x 10 -24 g)

6. NEUTRON  Third major subatomic particle discovered (1932 James Chadwick)  No charge (neutral)  Relative Mass of 1 AMU (1.675 x 10 -24 g)

7. ISOTOPES  Atoms of the same element have the same atomic number (# of protons) and the same chemical properties.  However, atoms of the same element may have different numbers of neutrons (and therefore different atomic mass)  Isotopes are atoms of the same element having different number of neutrons

10. NATURALLY OCCURRING ISOTOPES  Every element has naturally occurring isotopes  Hydrogen has 3 naturally occurring isotopes  Protium is the most abundant isotope of hydrogen (99.985%) has 1 proton, 0 neutrons, and 1 electron  Deuterium (0.015%) has 1 proton, 1 neutron, and 1 electron  Tritium (0.0001% ?) has 1 proton, 2 neutrons, and 1 electron

12. ISOTOPE EXAMPLE 35 Cl 37 Cl17 chlorine - 35 chlorine - 37

13. ISOTOPES OF CARBON Naturally occurring carbon consists of three isotopes, 12 C, 13 C, and 14 C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12 C 13 C 14 C 6 6 6 #P _______ _______ _______ #N _______ _______ _______ #E _______ _______ _______

14. SOLUTION 12 C 13 C 14 C 6 6 6 #P __6___ _ 6___ ___6___ #N __6___ _ _7___ ___8___ #E __6___ _ 6___ ___6___

15. ZINC PROBLEM An atom of zinc has a mass number of 65. A.Number of protons in the zinc atom B.Number of neutrons in the zinc atom C. What is the mass number of a zinc isotope with 37 neutrons?

16. ATOMIC MASS Listed on the periodic table Gives the mass of “average” atom of each element compared to 12 C Average atom based on all the isotopes and their abundance % Atomic mass is not a whole number … mass number is a whole number Na 22.99

17. CALCULATING ATOMIC MASS Percent(%) abundance of isotopes Mass of each isotope of that element Weighted average = mass isotope 1 (%) + mass isotope 2 (%) + … 100 100

18. ATOMIC MASS OF MAGNESIUM 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% (24)(.787) + (25)(.1013) + 26(.1117) = 18.888 + 2.5325 + 2.9042 = 24.3 amu

19. ISOTOPES Two Categories  Unstable – isotopes that continuously and spontaneously break down/decay in other lower atomic weight isotopes  Stable – isotopes that do not naturally decay but can exist in natural materials in differing proportions

24. USES OF RADIOISOTOPES  Carbon 14 Dating (Geologic Time)  When the organism dies it stops taking in 14 C which disappears as it decays to 14 N  Americum-241 Used in smoke detectors  Cesuim-137 Used to treat cancerous tumors  Californium-252 Used to inspect luggage for explosives  Cobalt-60 Used to sterilize surgical equipment  Iodine-123 Used to treat thyroid disorders  Plutonium-238 Used to power NASA spaceships