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
(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
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
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
How to Use the Periodic Table
5
B10.61
Symbol
Atomic Mass
Atomic Number
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!
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
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
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)
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)
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