ch. 3: atomic structure the theory of the atom ________________, a famous greek teacher who lived in...
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Ch. 3: Atomic StructureThe 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 Figure 5.1)
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. The
electron has a _______ charge. It’s mass is much smaller than the other 2 subatomic particles, therefore it’s mass is usually ______________. Like a Nutrition label at Old Country Buffet.
(2) The proton has a ______ charge, and it was discovered in _________ by E. Goldstein.
Democritus
John Dalton
element
subatomic
1897(-)
ignored
(+)1886
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(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!
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)
neutral 1932mass
visible matter
nucleuselectron cloud
nucleus (p+ & n0)
e- cloud
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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.
•Or.....
Rutherford 1911
helium gold foil
detector
bounced back
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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
densetiny
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
protons
neutrons
electrons
subtract
atomic mass
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How to Use the Periodic Table
5
B10.61
Symbol
Atomic Mass
Atomic Number
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Practice Problems• Find the # of e-, p+ and n0 for sodium. (mass # = 23)
• Find the # of e-, p+ and n0 for uranium. (mass # = 238)
3) What is the atomic # and mass # for the following atom? # e- = 15; # n0 = 16
Atomic # = 11 11 electrons11 protons
# neutrons = 23-11 = 12
Atomic # = 92 92 electrons92 protons
# neutrons = 238-92 = 146
Atomic # = 15 = # e- = # p+ Mass # = p+ + n0 = 15+16 =31
The element is phosphorus!
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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 n0).
• Another way to write the isotopes in shorthand is as follows:
C Cl12
6
35
17
The top number is the ________ #, and the bottom # is the __________ number. Calculating the # n0 can be found by _____________ the #’s!
protons neutrons
massmasses
neutrons
atomic mass
mass atomic subtracting
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More Practice Problems• Find the # e-, p+ and n0 for Xe-131.
• Find the # e-, p+ and n0 for
3) Write a shorthand way to represent the following isotope:
# e- = 1 # n0 = 0 # p+ = 1
Cu63
29
Atomic # = 54 n0 = 131-54 = 77Electrons = 54
Protons = 54
Atomic # = 29 = p+ = e- n0 = 63-29 = 34
Atomic # = p+ = e- = 1 mass # = n0 + p+ = 1+ 0 = 1
H-1 or H1
1
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Atomic Mass• Based on the relative mass of Carbon-12 which is exactly
_______.
• 1 p+ ≈ __ atomic mass unit (amu) 1 n0 ≈ __ 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 AveragePractice Problems: (1) Señorita Schwartz's Spanish 1 semester grades are calculated using a
weighted average of three category scores: Major Grades= 60% of your gradeMinor Grades= 30% of your gradeSemester 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)
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Weighted AverageStep (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)
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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
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.
Barely over 16.0 amu.
+
35.4951 amu