1. Ch. 3: Atomic Structure The Theory of the Atom ________________, a famous Greek teacher who lived in the 4th Century B.C., first suggested the idea of the atom. ________ __________ came up with his atomic theory based on the results of his experiments. (See p. 56) The Atom The smallest particle of an ________________ is an atom. The atom is made up of three ________________ particles. (1)The electron was discovered in _______ by J. J. Thomson by using a cathode ray tube. The electron has a _______ charge. It’s mass is much smaller than the other 2 subatomic particles, therefore it’s mass is usually ______________. Democritus John Dalton element subatomic 1897 (−)(−) ignored

2. Cathode Ray Tube

3. (2) The proton has a ______ charge, and it was discovered in _________ by E. Goldstein. (3) The neutron does not have a charge. In other words, it is ________. It was discovered in ____ by James Chadwick. The neutron has about the same _________ as the proton. These three particles make up all the ____________________ in the Universe! There are other particles such as neutinos, positrons, and quarks, but are typically left for 2 nd year chemistry courses. neutral1932 mass visible matter (+) 1886

4. Nuclear Atomic Structure The atom is made up of 2 parts/sections: (1) The ______________ --- (in the center of the atom) (2) The ____________ _________ --- (surrounds the nucleus) nucleus electron cloud (p + & n 0 ) e − cloud

5. The Nucleus Discovered by Ernest ________________ in ________. He shot a beam of positively charged “alpha particles”, which are ___________ nuclei, at a thin sheet of ______ _____. 99.9% of the particles went right on through to the ______________. Some were slightly deflected. Some even ____________ ________ towards the source! This would be like shooting a cannon ball at a piece of tissue paper and having it bounce off. Rutherford1911 heliumgold foil detector bounced back

6. Rutherford’s Experiment

8. Conclusions about the Nucleus (1) Most of the atom is more or less _________ ___________. (2) The nucleus is very _________. (Stadium Analogy) (3) The nucleus is very ___________. (Large Mass ÷ Small Volume) (4) The nucleus is ______________ charged. empty space dense tiny positively Counting Subatomic Particles in an Atom The atomic # of an element equals the number of ____________ in the nucleus. The mass # of an element equals the sum of the _____________ and ______________ in the nucleus. In a neutral atom, the # of protons = # of ______________. To calculate the # of neutrons in the nucleus, ______________ the ___________ # from the __________ #. protons neutrons electrons subtract atomic mass

9. Practice Problems (1)Find the # of e -, p + and n 0 for sodium. (mass # = 23) 2)Find the # of e -, p + and n 0 for uranium. (mass # = 238) 3) What is the atomic # and mass # for the following atom? # e - = 15; # n 0 = 16 Atomic # = 11 = # e - = # p + # neutrons = 23-11 = 12 Atomic # = 92 = # e - = # p + # neutrons = 238-92 = 146 Atomic # = 15 = # e - = # p + Mass # = p + + n 0 = 15+16 =31 The element is phosphorus!

10. Isotopes An isotope refers to atoms that have the same # of ___________, but they have a different # of ___________. Because of this, they have different _________ #’s (or simply, different ___________.) Isotopes are the same element, but the atoms weigh a different amount because of the # of ______________. Examples---> (1) Carbon-12 & Carbon-13 (2) Chlorine-35 & Chlorine-37 (The # shown after the name is the mass #.) For each example, the elements have identical ___________ #’s, (# of p + ) but different _________ #’s, (# of n 0 ). Another way to write the isotopes in shorthand is as follows: CCl 12 6 35 17 The top number is the ________ #, and the bottom # is the __________ number. Calculating the # n 0 can be found by _____________ the #’s! protons neutrons mass masses neutrons atomic mass atomic subtracting

11. Figure 3.10: Two isotopes of sodium.

12. More Practice Problems (1)Find the # e -, p + and n 0 for Xe-131. 2)Find the # e -, p + and n 0 for 3) Write a shorthand way to represent the following isotope: # e - = 1 # n 0 = 0 # p + = 1 Cu 63 29 Atomic # = 54 = p + = e − n 0 = 131 − 54 = 77 Atomic # = 29 = p + = e − n 0 = 63 − 29 = 34 Atomic # = p + = e − = 1 mass # = n 0 + p + = 1+ 0 = 1 H-1 orH 1 1

13. Ions An atom can gain or lose electrons to become electrically charged. Cation = (___) charged atom created by ___________ e-’s. –Cations are ______________ than the original atom. –_____________ generally form cations. Anion = (___) charged atom created by _____________ e-’s. –Anions are ____________ than the original atom. – _______________ generally form anions. Practice Problems: Count the # of protons & electrons in each ion. a) Mg +2 p + = _____ e − = ______ b) F −1 p + = _____ e − = ______ +losing smaller Metals −gaining larger Nonmetals 1210 9

14. Atomic Mass Based on the relative mass of Carbon-12 which is exactly _______. 1 p + ≈ __ atomic mass unit (amu) 1 n 0 ≈ __ amu 1e - ≈ __ amu The atomic masses listed in the Periodic Table are a “weighted average” of all the isotopes of the element. 12 1 1 0 Weighted Average Practice Problems: (1) Mr. Turkowski’s Algebra 1 semester grades are calculated using a weighted average of three category scores: Major Grades= 60% of your grade Minor Grades= 30% of your grade Semester Exam=10% of your grade If a student had the following scores, what would they receive for the semester? Major= 80 (B − ) Minor= 60 (D −) Semester Exam=65 (D)

15. Weighted Average Step (1): Multiply each score by the % that it is weighted. Step (2): Add these products up, and that is the weighted average! 60% x 80 = 48.0 30% x 60 = 18.0 10% x 65 = 6.5 Add them up!! A “normal average” would be calculated by simply adding the raw scores together and dividing by 3… 80 + 60 + 65 = 205 ÷ 3 = 68.3 = D + 72.5 (C−)

16. Average Atomic Mass Practice Problems: (2) In chemistry, chlorine has 2 isotopes: Cl-35 (75.8% abundance) Cl-37 (24.23 % abundance) What is the weighted average atomic mass of chlorine? 35 x 0.758 = 26.53 37 x 0.2423 = 8.9651 Add them up!!! (3) Oxygen has 3 isotopes: O-16 (99.76%) O-17 (0.037%) O-18 (0.2%) Estimate oxygen’s average atomic mass. + 35.4951 amu Barely over 16.0 amu

17. (4) Copper has an average atomic mass of 63.546 g/mole. It contains only two natural isotopes, which are Cu-63, with an isotope mass of 62.940 and Cu-65 with an isotope mass of 64.928. What are the percent of the two isotopes in naturally occurring copper?