Download The Atom

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%)