Chapter 4: Atomic Structure

1. Chapter 4: Atomic Structure Distinguishing Among Atoms

2. Learning Targets • You will determinethe parts of the atom and the function of each subatomic particle. • You will identifyisotopes, how to write them and how to determine average atomic mass.

3. Funnies  • Two molecules are walking down the street; one bumps into the other and says: • "Oh, my fault, you okay?” • The Second Molecule says: "No, I'm not ok, I've lost an electron!" So the first molecule says: "Are you sure" the second molecule answers, "I'm positive!" You will determinethe parts of the atom and the function of each subatomic particle. You will identifyisotopes, how to write them and how to determine average atomic mass.

4. The atom Symbols to be familiar with: • Protons = p+ • Neutrons = n0 • Electrons = e- • Atoms are always neutral • Neutral = Same number of protons and electrons You will determinethe parts of the atom and the function of each subatomic particle.

5. The symbol for an atom A X Z • A = the mass number (# p+ + n0) • X = symbol of element • Z = the atomic number (number of protons) You will identifyisotopes, how to write them and how to determine average atomic mass.

6. Isotopes • Isotopes are atoms that have the same number of protons, different number of neutrons • Often represented as: element name – mass #. (Example: lithium – 6) You will identifyisotopes, how to write them and how to determine average atomic mass.

7. Practice • Give the number of protons, neutrons and electrons in the atom symbolized by 201 Hg 80 • Give the symbol to represent the following information: • The cesium atom with a mass number of 132 You will identifyisotopes, how to write them and how to determine average atomic mass.

8. Try on your own • Give the number of protons, neutrons and electrons in the atom symbolized by 90 Sr 38 Strontium-90 occurs in fallout from nuclear testing. It can accumulate in bone marrow and may cause leukemia and bone cancer. • Give the symbol to represent the following information: • The iron atom with a mass number of 56 You will identifyisotopes, how to write them and how to determine average atomic mass.

9. Ions • Ions are atoms with a charge • cations (positively charged ion) • anions (negatively charged ion) • Ions have a charge because they are gaining or losing electrons from their neutral atom • Symbol is element symbol with the ion charge as a superscript (Example: Ca2+) • Usually formed when metals combine with nonmetals You will identifyisotopes, how to write them and how to determine average atomic mass.

10. Ions that certain groups form on the periodic table You will identifyisotopes, how to write them and how to determine average atomic mass.

11. Examples • For each of the following ions, indicate the total number of protons and electrons in the ion. A. Co2+ E. S2- B. Co3+ F. Sr2+ C. Cl- G. Al3+ D. K+ H. P3- You will identifyisotopes, how to write them and how to determine average atomic mass.

12. Examples-Answers • A. 27 p, 25 e B. 27 p, 24 e • C. 17 p, 18 e D. 19 p, 18, e • E. 16 p, 18 e F. 38 p, 36 e • G. 13 p, 10 e H. 15 p, 18 e You will identifyisotopes, how to write them and how to determine average atomic mass.

13. Calculating average atomic mass • Isotopes exist in different abundances. For example, an element may have 3 isotopes but one exists over 90%, another less than one % and another less than 10% • To continue with that example, each isotope has a respective mass with each percent it represents. You will identifyisotopes, how to write them and how to determine average atomic mass.

14. How to calculate average atomic mass • Change each percent to decimal. • Multiply each decimal and its respective mass for each pair of numbers they give. • Add the multiplied values together and round off based on significant digits (match up the mass you calculated to an element on the periodic table to be sure). You will identifyisotopes, how to write them and how to determine average atomic mass.

15. Example An element consists of 90.51% of an isotope with a mass of 19.922 amu, 0.27% of an isotope with a mass of 20.994 amu and 9.22% of an isotope with a mass of 21.990 amu. Calculate the average atomic mass and identify the element. You will identifyisotopes, how to write them and how to determine average atomic mass.

16. Example cont. • 1. Change each percent to decimal form 90.51%  .9051 0.27%  .0027 9.22%  .0922 • 2. Multiply each decimal number and its respective mass for each pair of numbers given. 90.51%  .9051 x 19.922 amu 0.27%  .0027 x 20.994 amu 9.22%  .0922 x 21.990 amu You will identifyisotopes, how to write them and how to determine average atomic mass.

17. Example cont. • 3. Add the multiplied numbers together, round off to significant digits • (.9051 x 19.922 amu = ) + (.0027 x 20.994 amu = ) + (.0922 x 21.990 amu = ) ELEMENT? You will identifyisotopes, how to write them and how to determine average atomic mass.

18. Try on your own • The element magnesium has three stable isotopes with the following masses and abundances: Isotopes Mass (amu) Abundance Mg-24 23.9850 78.99% Mg-25 24.9858 10.00% Mg-26 25.9826 11.01% Calculate the average atomic mass of Mg. You will identifyisotopes, how to write them and how to determine average atomic mass.

19. Answer • 24.30501576 rounds to 24.31 • Can compare with mass on periodic table to make sure correct. You will identifyisotopes, how to write them and how to determine average atomic mass.

20. Homework • Page 122-123 • 42, 45, 47-53, 54-57, 60, 63-64, 67, 70-71 You will determinethe parts of the atom and the function of each subatomic particle. You will identifyisotopes, how to write them and how to determine average atomic mass.