Atomic Theory #1
1. Fill in the following table with missing information.
Isotope
Mass
number
Atomic
number
192
78
#
Protons
#
#
Electrons Neutrons
4. Antimony has two isotopes. Sb-121 has a mass of
120.903824 amu with an abundance of 57.30% and Sb-123
has a mass of 122.904222 amu with an abundance of 42.70%.
What is antimony's average atomic mass?
Fe-58
8
8
16
2. Draw the Bohr model for the sodium atom.
3. Draw the Bohr model for the chlorine atom.
9
8
18
5. Cerium has four isotopes:
Ce-136
135.907140 amu
0.19% abundance
Ce-138
137.905996 amu
0.25% abundance
Ce-140
139.905442 amu
88.48% abundance
Ce-142
141.909249 amu
11.08% abundance
What is the average atomic mass of cerium?
6.. Neon has three isotopes, Ne-20, 19.992439 amu with an
abundance of 90.60%, Ne-21, 20.993845 amu with an
abundance of 0.26%, and Ne-22, 21.991384 amu with an
abundance of 9.20%. What is its average atomic mass?
Atomic Theory #2
Electron configurations!
Group 1 Alkali metals:
Give the electron configuration for the following elements:
Li:____________________________________________
Na:
____________________________________________
K:
____________________________________________
Where are these elements found on the periodic table?
How are these configurations similar?
Group 2 Alkaline Earth metals:
Give the electron configuration for the following elements:
Mg:____________________________________________
Ca:
____________________________________________
Sr:
____________________________________________
Where are these elements found on the periodic table?
How are these configurations similar?
Group 8 Noble Gases:
Give the electron configuration for the following elements:
He:____________________________________________
Ne:
____________________________________________
Kr:
____________________________________________
Where are these elements found on the periodic table?
How are these configurations similar?
Transition Metals:
Give the electron configuration for the following elements:
Mn:____________________________________________
Ag:
____________________________________________
Au:
____________________________________________
____________________________________________
Where are these elements found on the periodic table?
How are these configurations similar?
Average Atomic Mass
Okay, so you should now have a basic understanding of what an
isotope is. Just for my benefit, define isotope here:
An isotope is:_______________________________________.
When you look at the periodic table, the atomic mass number
provided is an AVERAGE of all the isotopes of that element based
on how ABUNDANT the isotopes are in nature.
For example, uranium has three different isotopes. Scientists use
a tool called a mass spectrometer to determine the masses and
abundances shown below. Based on the mass numbers provided
(round them to nearest whole number), determine the number of
protons and neutrons for each of uranium's isotopes.
protons
U-234
U-235
U-238
neutrons
Mass of isotope
234.040947 amu
235.043925 amu
238.050786 amu
Abundance
0.0060%
0.72%
99.27%
Look on the periodic table. What is the average atomic mass of
uranium? _____________amu
The way that this number is determined is by "weighting" the
mass of each isotope based on its abundance and then adding
those weighted masses together. This is done mathematically by
multiplying the mass of each isotope by its abundance in decimal
form. (To convert from percent to decimal form of abundance,
simply mover the decimal two places to the left.)
Example:
Uranium-234 has a mass of 234.040947 and an abundance of
0.0060%
(234.040947)(0.00006) = 0.014
Uranium-235 has an abundance of 235.043925 and an abundance
of 0.72%.
(235.043925)(0.0072) = 1.7
Uranium-238 has an abundance of 238.050786 and an abundance
of 99.27%
(238.050786)(.9927) = 236.31
SO…
236.31 + 1.7 + .014 = 238.0 which is the average
atomic mass of uranium.
(why did I keep only one place after the decimal?)
So, to calculate average atomic mass, you must take two steps
mathematically:
Step 1:
Step 2:
In class, you be provided with the isotopes of the several
elements with their abundance and exact mass. (This is also
available on-line; just do a google search.) Determine the average
atomic mass of four different elements, using this information.
One of them must have at least four isotopes and you may not use
an element with only one isotope. Show all work for credit.
Atomic Theory #3 Practice Test
1. Match the scientist with his/her discovery and the
experimental apparatus used (if given):
_____ Chadwick
a. first described atom’s behavior
_____ Bohr
b. gold foil experiment
_____Thomson
c. protons in nucleus
_____ Dalton
d. electron
_____ Rutherford
e. electron energy levels
_____Curie
f. cathode ray tube experiments
g. neutron
2. List the five components of Dalton’s atomic theory:
1.
2.
3.Fill in the following table:
Isotope
Mass
number
Atomic
number
112
50
#
Protons
#
#
Electrons Neutrons
Se-76
11
15
30
12
16
34
4. What is the average atomic mass of sulfur?
S-32
31.972072 amu
95.05% abundance
S-33
32.971459 amu
0.75% abundance
S-34
33.967868 amu
4.21% abundance
S-36
35.967079 amu
0.020% abundance
5. Give the electron configuration for:
3.
4.
5.
Cl:
_____________________________________________
Cr:
_____________________________________________
Cu:
_____________________________________________
6. Why do different elements give off specific colors when
exposed to heat?
Flame Test Lab Exercise
When elements are heated to high temperatures, their
electrons become excited. This causes the electrons to
move into higher energy levels. As they return to their
initial energy state, they emit light. Each type of element
gives off a specific color of light when it is heated or
excited. The color of light given off by an atom can be used
to identify it. In this lab, you will observe and record the
colors given off by several different metal ions when they
are heated in a Bunsen burner flame.
Data Collection:
Create a table of two columns and eight rows. The first
column should be labeled “Ion type” and the second column
should be labeled “Color when heated”. The rows in the first
column should be labeled with the following ions: Na+, K+,
Ca2+, Sr2+, Li+, Ba2+, Cu2+. The rows in the second column
should be left blank. You will record your observations here.
Lab Procedure:
1. Obtain the following: nichrome loop, about 30 mL of
HCl acid in a small beaker, 2 watch glasses.
2. Wash and dry watch glass. Obtain small quantity (a
couple of pinches) of one of the following salts on one
of the watch glasses:
-strontium chloride (SrCl2)
-calcium nitrate (Ca(NO3)2)
-barium nitrate (Ba(NO3)2)
-potassium nitrate (KNO3)
-lithium chloride (LiCl)
-copper (II) bromide (CuBr2)
-sodium nitrate (NaNO3)
3. Clean the nichrome loop by dipping it in the HCl and
then placing it in the Bunsen burner flame until no
color is imparted from the wire.
4. Place a small quantity of distilled water on the second
watch glass. Dip the loop into this water to moisten it.
5. Dip the moist loop into the salt on the watch glass.
6. Place the loop in the Bunsen burner flame. Observe
the color that emits from the loop. Record this color
in your data table.
7. When no more color emits from the loop, clean it by
dipping it once again in the HCl and burning it in the
flame.
8. Repeat steps 2 through 7 with each of the remaining
salts. Wash and dry watch glass before obtaining a
new salt. Avoid contaminating the HCl and distilled
water with the ionic compounds. If you suspect you
have contaminated them, please replace them with
fresh quantities.
9. When you have tested all 7 of the salts, obtain a small
quantity of unknown salt. Repeat steps 2 through 7
with the unknown salt. Record the color of the flame
observed with the unknown salt in your lab book.
Identify the unknown based on its flame color and
record in your book.
WARNING: The HCl (hydrochloric acid) you will be using is
concentrated and dangerous. Take extra care when handling
it and immediately rinse skin if contact occurs. Notify
instructor immediately if a spill occurs. Do not taste or
touch the salts. They may cause skin irritation.
Flame Test Lab Questions
Answer questions using complete sentences in your lab book.
Be thorough in your answers for full credit.
1. Which elements were the easiest to distinguish using the
flame tests? Which were the most difficult? Give a reason
for each answer.
2. What do you think was the most dangerous part of this
lab? Give a reason for your answer.
3. Explain why atoms of different elements give off
different colors of light using atomic theory and electron
configuration knowledge.
4. How would you rate your performance in lab during this
exercise? Give two reasons to support your rating.
5. How would you improve your performance next time in
lab? Remember each lab is a learning experience and you
have not reached perfection yet.
6. What was the unknown? How do you know?