Chapter 4
ATOMIC STRUCTURE
ATOMS : “Smallest” building blocks of matter.
made up of...
protons (+) [p+]
neutrons (0) [n]
electrons (-) [e-]
Symbol # p+ #e-
Name
1
1
#n Atomic Mass
#
#
0
1
1
C
6
6
6
Hydrogen-1
1
Carbon-12
12
H
6
12
Gold-197
197
Au
79
79 118
79
197
Chlorine-35
35
Cl
17
17
18
17
35
Chlorine-36
36
17
17
19
17
36
Cl
mass of PROTON
=
mass of NEUTRON =
mass of ELECTRON =
1 amu
1 amu
0.00055 amu
NOTE: 1 gram = 6.02(10)23 amu
CHEMISTRY – Chapter 4 – Scotch Plains-Fanwood High School
Page 1
ISOTOPES
Atoms of the same element with DIFFERENT #
neutrons
naturally occurring
Atomic Mass
Name
55 e-
55 e-
55 e-
55 p+
77 n
55 p+
78 n
55 p+
79 n
132
133
134
cesium-132
Abundance
cesium-133 cesium-134
20.00%
75.00%
5.00%
Find: “average” atomic mass of cesium using above info:
0.2000
0.7500
0.0500
x
x
x
132.0
133.0
134.0
=
=
=
CHEMISTRY – Chapter 4 – Scotch Plains-Fanwood High School
26.40
99.75
6.70
132.85 amu
Page 2
ws – Atomic Structure
Directions: Fill in the following table for all NEUTRAL atoms
Name
1
Symbol # p+ #e- #n Atomic Mass
#
#
13
14
59
2
Ni
3
47
4
Calcium-41
5
Iron-55
6
64
Zn
7
8
109
12
22
27
60
9
10
CHEMISTRY – Chapter 4 – Scotch Plains-Fanwood High School
28
78
24
196
Page 3
ws – Isotopes and Average Atomic Mass
Directions: Find the average atomic mass for each of the following elements based on
their relative abundances. Report answers to the nearest 0.01 amu.
1. 80% 127I, 17% 126I, 3% 128I
2. 50 % 197Au, 50% 198Au
3. 15% 55Fe, 85% 56Fe
4. 99% 1H, 0.8% 2H, 0.2% 3H
5. 95% 14N, 3% 15N, 2% 16N
6. 98% 12C, 2% 14C
CHEMISTRY – Chapter 4 – Scotch Plains-Fanwood High School
Page 4
Lab-Modeling Isotopes – Chapter 4
Name _____________________ Partner ____________________ Date ___________ Period __
Purpose: To model how to determine the average atomic mass of an element using relative
abundances of isotopes.
PART I
Procedure:
1. Find the average mass of a pre-1982 penny using 10 pennies and fill in 1st table below
using the balance.
2. Find the average mass of a post-1983 penny using 10 pennies and fill in 1st table below
using the balance.
3. Find the average mass of each of the combinations of pennies listed in the 2nd table below
using the balance.
4. Show a calculation to find the predicted average mass of each of the combinations of
pennies listed in the 3rd table below.
Data:
# pre-1982 pennies
# post-1983 pennies
Average penny mass
10
0
Pre-1982 penny = (____________ g)
0
10
Post-1983 penny = ((____________ g))
# pre-1982
pennies
1
# post-1983
pennies
9
2
8
3
7
4
6
5
5
6
4
7
3
8
2
9
1
Total mass (g)
CHEMISTRY – Chapter 4 – Scotch Plains-Fanwood High School
Average penny mass (g)
Page 5
Calculations: PREDICT the average penny mass for each combination
% pre-1982 pennies x mass
0.10 x (____________ g)
% post-1983 pennies x mass
+
0.90 x ((____________ g))
Average penny mass
=
______________ g
______________ g
______________ g
______________ g
______________ g
______________ g
______________ g
______________ g
______________ g
CHEMISTRY – Chapter 4 – Scotch Plains-Fanwood High School
Page 6
PART II: Identify which “Mystery Envelopes” containing 10 pennies each
correspond to the percentages below and your data from the tables above:
Mystery Envelopes Data
Envelope Envelope Mass
#
alone (g)
Total Mass (g)
Penny Mass
Alone (g)
Average Mass
per Penny (g)
1
2
3
4
5
6
7
8
9
MYSTERY ENVELOPE
% pre-1982 pennies
% post-1983 pennies
10%
90%
20%
80%
30%
70%
40%
60%
50%
50%
60%
40%
70%
30%
80%
20%
90%
10%
CHEMISTRY – Chapter 4 – Scotch Plains-Fanwood High School
Average Penny Mass
CODE
Page 7
ACTIVITY - Model for Atomic Dimensions
+
-
p mass = n mass = 1840 * e mass
+
nuclear mass = mass p + mass n = mass number of atom
atomic radius = nuclear radius * 10,000.
1 lb = 454 g
1 inch = 2.54 cm
1 mile = 5,280 ft
1.
Find the mass of the smaller spherical object which will represent one e -.
_________ grams
2. Calculate the TOTAL mass [in grams] of a carbon-14 atom based on the mass of
the “electron” above and formulas given above. [Hint: how many p+, n, and e- are there
and what mass would each one have?]
Number of
Mass of each
Total mass
p+:
______
_________ ___
___________ ___
n:
______
_________ ___
___________ ___
e-:
______
_________ ___
___________ ___
_________ grams
3.
Convert the atomic mass above [mass of a carbon-14 atom] to pounds.
This # represents how much an atom weighs in relation to the “e-” mass above. _________ lbs
-------------------------------------------------------------------------------------------------------------------4. a. Find the radius [in cm.] of the larger spherical object which will represent the
“nucleus” of the atom.
_________ cm
b. Use the nuclear radius above to find the atomic radius.
_________ cm
5.
Convert the value for the atomic radius to yards.
This # represents how BIG an atom is in relation to the “atomic radius” above.
CHEMISTRY – Chapter 4 – Scotch Plains-Fanwood High School
_________ yards
Page 8