Atomic Theory and the Nuclear Atom
Unit 2 Page 2
Atomic Theory Practice
1. Who bombarded gold foil with alpha particles?
2. Who devised the first atomic theory?
9. Who determined that the mass of an atom was
concentrated in the center?
10. Who showed cathode rays are composed of
negative particles?
3. Who developed the planetary model of the atom?
4. Who discovered the first subatomic particle?
5.
Who discovered the nucleus?
6. Who devised the plum pudding (chocolate chip
cookie) model?
7.
Who was the first to suggest electrons had a
fixed energy?
8. Who said that all atoms of an element are
identical in size, mass and other properties?
11. Who discovered the atom is made up of mostly
empty space?
12. Who had the idea of a basic indivisible particle?
13. Who concluded that all elements contain
electrons?
14. Who conducted an experiment using Cathode Ray
Tubes?
15. Who said atoms are neither created, nor
destroyed—just rearranged?
Atomic Theory and the Nuclear Atom
Unit 2 Page 4-5
Structure of an Atom and Isotopes Practice
Complete the following table using your knowledge of atomic structure:
Element
Hyphen
notation
Atomic
Number
Number of
Protons
Number of
Neutrons
Number of
Electrons
Mass
Number
1
1
H
2
1
H
12
6
C
13
6
C
35
17
Cl
37
17
Cl
24
12
Mg
26
12
Mg
30
27
66
32
Consider the following sets of isotopes and then explain the similarities and differences between each set.
Set I
Set II
12
6
C
13
C
6
24
Mg
12
26
Mg
12
Atomic Theory and the Nuclear Atom
Unit 2 Page 6
Average Atomic Mass Practice
1. Silicon has three, stable, naturally occurring isotopes. These are silicon-28, silicon-29, and silicon-30. The relative
abundance of each is 92.21%, 4.70%, and 3.09% respectively. ESTIMATE the value of the answer before you begin. Will
the weighted average be closer to 28, 29, or 30? Why? What is the average atomic mass of silicon?
2. For every 100 atoms of hafnium, 5 have a mass of 176amu, 19 have a mass of 177amu, 27 have a mass of 178amu, 14
have a mass of 179amu, and 35 have a mass of 180amu. What is the average atomic mass of hafnium?
3. Chlorine has two, stable, naturally occurring isotopes. These are chlorine-35 and chlorine-37. The relative
abundance of each is 75.77%, and 24.23% respectively. What is the average atomic mass of chlorine?
127
4. Iodine is 80%
53
I, 17%
126
53
I, and 3%
128
53
I. Calculate the average atomic mass of iodine.
5. The average atomic mass of iron is 55.9002amu. Iron has four, stable, naturally occurring isotopes. Three of these
isotopes are iron-54, iron-57, and iron-58. The relative abundance of each is 5.90%, 2.10%, and 0.280% respectively.
What is the mass of the fourth isotope?
6. Determine the average atomic mass using the mass spec shown below. Which element is most likely shown here?
7. CHALLENGE! Calculate the average atomic mass of magnesium using the following data for three, stable magnesium
isotopes. It is important to understand that the masses of a proton and neutron are approximately 1amu. Therefore, as
you will notice, in the table below each isotope’s actual mass isn’t a whole number (but very close to it).
Isotope
mass (u)
relative abundance
Mg-24
23.985
78.70%
Mg-25
24.986
10.13%
Mg-26
25.983
11.17%
Atomic Theory and the Nuclear Atom
Unit 2 Page 7
Moles Practice
1. How many moles of nickel are in 82.34 grams of nickel?
2. If there are 9.32x1024 molecules of fluorine (F2), how many moles is that?
3. In 4.23 moles of magnesium, how many atoms will you have?
4. Given a sample of 2.97 moles of chlorine (Cl2),
a) how many molecules of Cl2 are in your sample?
b) how many atoms of Cl2 are in your sample?
5. If 13.19 moles of titanium are needed to be used to make joint replacement materials, how may grams
of titanium is needed?
6. How many atoms of oxygen are in 3.12 moles of O2 (oxygen gas)?
7. What is the mass in grams of 3.00mol of the element carbon?
8. How many atoms of carbon are in 45.98g of Na?
9. How many grams are equal to 1.20x1024 molecules of Cl2?