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

Cathode Ray Tube

(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

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

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

Rutherford’s Experiment

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

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 = = 12 Atomic # = 92 = # e - = # p + # neutrons = = 146 Atomic # = 15 = # e - = # p + Mass # = p + + n 0 = =31 The element is phosphorus!

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 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

Figure 3.10: Two isotopes of sodium.

More Practice Problems (1)Find the # e -, p + and n 0 for Xe )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 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

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

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 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)

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 = % x 60 = % x 65 = 6.5 Add them up!! A “normal average” would be calculated by simply adding the raw scores together and dividing by 3… = 205 ÷ 3 = 68.3 = D (C−)

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 = x = 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 amu Barely over 16.0 amu

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