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Ch. 3: Atomic Structure The Theory of the Atom • ________________, a famous Greek teacher who lived in the 4th Democritus Century B.C., first suggested the idea of the atom. John __________ Dalton came up with his atomic theory based on • ________ the results of his experiments. (See Figure 5.1) The Atom element • The smallest particle of an ________________ is an atom. • subatomic The atom is made up of three ________________ particles. 1897 by J. J. Thomson. The (1)The electron was discovered in _______ (-) charge. It’s mass is much smaller than the electron has a _______ other 2 subatomic particles, therefore it’s mass is usually ______________. Like a Nutrition label at Old Country Buffet. ignored (+) charge, and it was discovered in (2) The proton has a ______ 1886 by E. Goldstein. _________ (3) The neutron does not have a charge. In other words, it is ________. ____ by James Chadwick. neutral It was discovered in 1932 mass as the proton. The neutron has about the same _________ visible matter • These three particles make up all the ____________________ in the Universe! Nuclear Atomic Structure • The atom is made up of 2 parts/sections: (1) The ______________ --- (in the center of the atom) nucleus electron _________ cloud (2) The ____________ --- (surrounds the nucleus) nucleus (p+ & n0) e- cloud The Nucleus • Discovered by Ernest ________________ in ________. Rutherford 1911 • He shot a beam of positively charged “alpha particles”, which helium gold _____. foil are ___________ nuclei), at a thin sheet of ______ • 99.9% of the particles went right on through to the ______________. detector • Some were slightly deflected. Some even ____________ ________ bounced back towards the source! • • This would be like shooting a cannon ball at a piece of tissue paper and having it bounce off. •Or..... Conclusions about the Nucleus empty ___________. space (1) Most of the atom is more or less _________ (2) The nucleus is very _________. (Stadium Analogy) tiny dense (3) The nucleus is very ___________. (Large Mass ÷ Small Volume) positively (4) The nucleus is ______________ charged. Counting Subatomic Particles in an Atom protons • The atomic # of an element equals the number of ____________ in the nucleus. protons • The mass # of an element equals the sum of the _____________ and neutrons ______________ in the nucleus. electrons • In a neutral atom, the # of protons = # of ______________. subtract • To calculate the # of neutrons in the nucleus, ______________ the atomic # from the __________ mass ___________ #. How to Use the Periodic Table 5 B 10.61 Atomic Number Symbol Atomic Mass Practice Problems • Find the # of e-, p+ and n0 for sodium. (mass # = 23) Atomic # = 11 11 electrons # neutrons = 23-11 = 12 11 protons • Find the # of e-, p+ and n0 for uranium. (mass # = 238) Atomic # = 92 # neutrons = 238-92 = 146 92 electrons 92 protons 3) What is the atomic # and mass # for the following atom? # e- = 15; # n0 = 16 Atomic # = 15 = # e- = # p+ Mass # = p+ + n0 = 15+16 =31 The element is phosphorus! Isotopes protons • An isotope refers to atoms that have the same # of ___________, neutrons but they have a different # of ___________. mass #’s (or simply, • Because of this, they have different _________ masses different ___________.) • Isotopes are the same element, but the atoms weigh a different neutrons amount because of the # of ______________. Examples---> (1) Carbon-12 & Carbon-13 (2) Chlorine-35 & Chlorine-37 (The # shown after the name is the mass #.) atomic • For each example, the elements have identical ___________ #’s, mass #’s, (# of n0). (# of p+) but different _________ • Another way to write the isotopes in shorthand is as follows: 12 6 C 35 17 Cl mass #, and the bottom # is the __________ atomic The top number is the ________ subtracting number. Calculating the # n0 can be found by _____________ the #’s! More Practice Problems • • Find the # e-, p+ and n0 for Xe-131. Atomic # = 54 n0 = 131-54 = 77 Electrons = 54 Protons = 54 63 + 0 Find the # e , p and n for 29Cu Atomic # = 29 = p+ = e- n0 = 63-29 = 34 3) Write a shorthand way to represent the following isotope: # e- = 1 # n0 = 0 # p+ = 1 Atomic # = p+ = e- = 1 H-1 or mass # = n0 + p+ = 1+ 0 = 1 1 1 H Atomic Mass 12 • Based on the relative mass of Carbon-12 which is exactly _______. 1 atomic mass unit (amu) • 1 p+ ≈ __ 1 amu 1 n0 ≈ __ 0 amu 1e- ≈ __ • The atomic masses listed in the Periodic Table are a “weighted average” of all the isotopes of the element. Weighted Average Practice Problems: (1) Señorita Schwartz's Spanish 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) 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!! 72.5 (C) 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 Weighted Average 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 35.4951 amu Add them up!!! (3) Oxygen has 3 isotopes: O-16 (99.76%) O-17 (0.037%) Estimate oxygen’s average atomic mass. Barely over 16.0 amu. O-18 (0.2%)