Chemists & Models of the Atom
Name________________________________
Period_______Date_____________________
Part I: Chemists in History - Write the name of the chemist who proposed each of the ideas listed below.
Some names may be used more than once.
Democritus
Franklin
Rutherford
Lavoisier
Thomson
Bohr
Proust
Becquerel
Moseley
Dalton
Marie & Pierre Curie
Modern Model
_____________________ 1. Stated that matter is neither created nor destroyed in chemical reactions.
_____________________ 2. Stated that a given compound always has the same relative number and
kinds of atoms.
_____________________ 3. Discovered radioactivity while working with a sample of Uranium.
_____________________ 4. Determined that a cathode ray is made of electrons.
_____________________ 5. Isolated two new elements, radium and polonium.
_____________________ 6. Understood the atom to have a central nucleus with electrons orbiting
around in fixed paths like planets around the sun.
_____________________ 7. Stated that all atoms of a given element are identical, but they differ from
those of other elements.
_____________________ 8. Stated that all matter is composed of tiny, indivisible particles called atoms.
_____________________ 9. Found that there are three types of natural radiation.
_____________________ 10. First person to suggest that the atom is related to electricity.
_____________________ 11. Uses Quantum Mechanics and states that the electron may be found in a
probability region.
_____________________ 12. Determined that each atom has it own atomic number (number of protons.)
_____________________ 13. Used Gold Foil to determine that all the positive matter (protons) is
concentrated into a very small, very dense nucleus and that most of the
atom is empty space.

Part II: Experiments about the Atom – Fill in the blanks with the appropriate word. Each word or
number will only be used once.
0
+2 anode electrons beta empty space cathode exposed
3 no gamma negative large positively mass proton (nucleus)
14. The negatively charged electrode of a cathode ray tube is the ___________________, the positively
charged electrode is called the ______________________.
15. In Thomson’s experiment, the cathode ray is deflected by the magnet, this indicated that the ray had
____________________. When the electrically charged plates were turned on, the cathode ray was
deflected toward the positive plate, this indicated that the beam had a ____________________ charge.
16. Therefore a cathode ray is made of a beam of ____________________.
17. Becquerel discovered radiation because a sample of uranium ore __________________ a piece of
photographic film.
18. Rutherford used a radioactive sample and determined that natural radiation has ______ components:
alpha particles which have a _______ charge and a relatively _______________ mass,
________________ particles which have a negative charge and a mass of ______ and
______________ rays which are neutral and have ________ mass.
19. Rutherford used alpha particles in his Gold Foil experiment. Because the alpha particles are relatively
large and positive the fact that most of them proceeded straight through the foil proved that the atom
is mostly _____________________________. Some of the positive alpha particles deflected directly back toward the source which indicated that the nucleus was _______________________ charged
Thus, Rutherford is credited with discovering the ___________________.
20. Draw a simple sketch of each chemist’s model of the atom. Indicate charge where needed.
Dalton Thomson Rutherford Bohr Modern Model

3.3 Practice
Protons, Neutrons and Electrons
21.
How many protons and electrons are in a vanadium atom?
22.
How many protons and electrons are present in a nitrogen atom?
23.
How many protons and electrons are present in an argon atom?
24.
How many protons and electrons are present in a potassium atom?
25.
How many protons and electrons are present in a platinum atom?
26.
What is the name of the element that has atoms that contain 5 protons?
27.
What is the name of the element that has atoms that contain 17 protons?
28.
What is the name of the element that has atoms that contain 25 protons?
29.
What is the name of the element that has atoms that contain 82 protons?
30.
What is the name of the element that has atoms that contain 92 protons?
31.
Write the chemical symbol for the ion with 12 protons and 10 electrons.
32.
Write the chemical symbol for the ion with 74 protons and 68 electrons.
33.
Write the chemical symbol for the ion with 95 protons and 89 electrons.
34.
Write the chemical symbol for the ion with 33 protons and 36 electrons.
35.
Write the chemical symbol for the ion with 29 protons and 27 electrons.

36.
How many protons, neutrons and electrons are present in the
59
28
37.
How many protons, neutrons and electrons are present in the
91 +4
40
Zr ion?
38.
How many protons, neutrons and electrons are present in the
140
58
Ce
+3 ion?
39.
How many protons, neutrons and electrons are present in the
79 -2
34
Se ion?
40.
How many protons, neutrons and electrons are present in the
45 +3
21
Sc ion?
41.
How many protons, neutrons and electrons are present in the
13 -4
6
C ion?
42.
Write the isotopic symbol for the ion with 84 protons, 125 neutrons and 80 electrons.
43.
Write the isotopic symbol for the ion with 27 protons, 32 neutrons and 25 electrons.
44.
Write the isotopic symbol for the ion with 73 protons, 108 neutrons and 68 electrons.
45.
Write the isotopic symbol for the ion with 31 protons, 39 neutrons and 28 electrons.
46.
Atomic Structure
1
2
3
4
Isotopic
Name
Zinc - 65
Isotopic
Symbol
Atomic #
2
35
Mass #
4
# of protons
# of neutrons
12
45
5
27
13
Al
# electrons
12

6
7
8
9
Uranium –
238
11
197 79
12
47 36
10
11
Titanium-
48
108 47
47.
Atomic Structure Practice Chart
1
2
3
Isotopic
Name
4 gold – 197
Isotopic
Symbol
# of protons
14
# of electrons
36
# of neutrons
15
136
Atomic # Mass #
86
5 20 21
17 6
48.
Complete the following table for the following ions:
Complete
Isotopic
Symbol
+
-
84
35
63
29
Cu + cation
8 15 -2
24 23 27
25 10 13

26 13 10
32 40 +4
83 86 126
Formation of Ions
49.
Calculate the charges on the following ions, and indicate whether the ion is a cation or anion.
Ion
Magnesium
Number of
Protons
12
Number of
Electrons
10
Charge Cation or
Anion?
Fluoride 9 10
Sulfide
Gold
16
79
18
76
50.
Consult the periodic table and give the symbol for the ions that have: a.
28 protons and 26 electrons ___________ b.
34 protons and 36 electrons ___________
51.
Complete the following table for ions:
Symbol for
Ion
Cl
-1
Mg +2
K +1
Atomic
Number
Mass
Number
37
24
39
Protons Neutrons Electrons Charge
O
-2
Al
+3
P
-3
16
30
31

52.
Write the symbol including the mass number, atomic number and charge for the ions containing the following numbers of protons, neutrons, and electrons.
A. 16 p
B. 35 p
+
+
, 16 n
, 45n


, 18 e
, 36 e
-
-
D. 1 p
+
E. 13 p
, 0 n
+

, 14 n
, 0 e

-
, 10 e
-
C. 20 p
+
, 20 n

, 18 e
-
F. 11 p
+
, 12 n

, 10 e
-
53.
Fill in the following table about the formation of ions.
Ion Symbol Charge Atomic # # of p
+
# of e
-
Ion formed by
Loss of 1 e
-
Potassium
Ba
+2
+4
-1
50
16
53
33 36
Gain of 2 e
-
+3 28
Isotopes and Average Atomic Mass and Ions
Elements come in a variety of isotopes, meaning they are made up of atoms with the same atomic number, but different atomic masses. These atoms differ in the number of neutrons. The average atomic mass if the weighted average of all the isotopes of an element.
Example: A sample of cesium is 75% 133
55
Cs , 20.% 132
55
Cs , and 5% 134
55
Cs .
What is the average atomic mass?
Answer: .75 x 133 = 99.75
.20 x 132 = 26.4
.05 x 134 = 6.7 +
Total = 132.85 amu = average atomic mass
Determine the average atomic mass of the following mixtures of isotopes.
_________________________________________________________________________________
54.
80.% 127
53
I , 17% 126
53
I , 3% 128
53
I

55.
50.% 197
79
Au , 50.% 198
79
Au
56.
15% 55
26
Fe , 85% 56
26
Fe
57.
99% 1
1
H , 0.8% 2
1
H , 0.2% 3
1
H
58.
95% 14
7
N , 3% 15
7
N , 2% 16
7
N
59.
98% 12
6
C , 2% 14
6
C
______________________________________________________________________
60.
Uranium has 3 isotopes with the following relative abundances: Uranium-234 (0.0058%),
U-235 (0.71%), and U-238 (99.23%). Calculate the average atomic mass of uranium:
61.
Fill in the blanks in the following table using the periodic table when necessary. If not otherwise noted,
assume the elements to be neutral atoms.
Symbol Protons Electrons Neutrons Mass Number Atomic Number
A
42
20
Ca +2
B 59 141
C 60 44
D
E
34
15
P -3
24 45
F 22 28
62.
Write the hyphen notation for each of the six isotopes listed above:
A. _____________________ B. _____________________ C. ____________________
D. _____________________ E. _____________________ F. ____________________

63.
Indicate the charge (+1, -1, etc) on the ions that are formed in the following situations. Record the
resultant ion as a cation or anion . a. Lithium loses 1 electron
Charge
_____________
Cation/Anion
_______________ b. Oxygen gains 2 electrons c. Magnesium loses 2 electrons d. Nitrogen gains 3 electrons
_____________
_____________
_______________
_______________
_____________ _______________
HISTORY OF THE ATOM REVIEW
64.
_______________ was the ancient philosopher who first proposed the existence of atoms.
65.
_______________ showed that matter is neither ___________________ nor _________________ in chemical reactions, and is known as the “Father of Chemistry.”
66.
_______________ created the first atomic theory. He thought that all atoms of an element are identical, and that atoms of different elements are different from each other. His model of the atom is represented below.
67.
The Law of ___________________ _____________________ states that compounds always have the same elements in the same ratio by mass.
68.
_____________________ discovered the electron using a cathode ray tube. Current flows from the
___________ to the ___________. Because the beam was deflected toward a positively charged plate
(Letter C), the beam must have a ___________ charge. Because the beam was also affected by a magnet (Letter A), cathode rays also have _______. This led to the __________ ____________ model of the atom, shown below.

69.
_______________________ is credited with discovering the nucleus of the atom, during his famous
__________________________experiment. He used a radioactive source to beam positively charged
_________ _________________ toward a very thin film of gold foil. Most of the particles
_______________________________________, but some were ____________ at various angles. From this he concluded that most of the atom is ___________________, with a small _______________ charged nucleus in the center, and the electrons somewhere outside. His experimental results and newer model of the atom are shown on the next page.
70.
_____________ proposed that electrons moved in fixed orbits around the nucleus, like planets around the sun - the ________ ___________ model. (Left below)
71.
In the modern model of the atom, the nucleus contains ___________ and ___________, with the
______________ outside in a cloud. (Right below)
72.
___________________ discovered radioactivity when pitchblende, an ore containing ______________, exposed photographic film. Rutherford later showed three types of radiation, by exposing a beam of

radiation to electrical plates. An Alpha particle is the same as a ___________ ___________, has a
___________ charge, so is attracted to the ____________ plate. Write the symbol for an alpha particle
___________. A Beta particle is the same as an _____________, has a ___________ charge, and is attracted to the ________ plate. The electron has less mass, so is deflected more. Gamma rays are pure
_________, have _____ charge, and thus are __________ by the electrical plates. Label the alpha and beta particles and gamma rays in the drawing below.
_
II. PROBLEMS:
73.
Summarize the information you have gained about subatomic particles in the table below:
Particle Symbol
Relative Mass
(AMU)
Electrical Charge
Location in the
Atom electron neutron proton
74.
Why are atoms electrically neutral?______________________________________________________
75.
Define the following terms:
A.
atomic number
B.
mass number
C.
isotope

D.
isotopic symbol
E.
average atomic mass
F.
ion
G.
charge
76.
A. A nitrogen atom has 7 protons and 7 neutrons. Calculate:
1. the atomic number ______ 2. the mass number ______
B. A phosphorus atom has 15 protons, 18 electrons, and 16 neutrons. Calculate:
1. the atomic number ______ 2. the mass number ______ 3. the charge
77.
If a sulfur atom is neutral in charge and contains 16 protons in the nucleus, how many electrons are
present outside the nucleus? ______
78.
Write the isotopic symbol for a lithium atom with 3 protons and 4 neutrons: _________
79.
Which of the following are isotopes of each other?
Why?______________________________________
A)
32
16
S B)
36
16
S
-2
C)
36
18
Ar
80.
An isotope of silver has 47 protons, 46 electrons and 60 neutrons.
A) What is the atomic number? ______
B) What is the mass number? ______
C) How many electrons are present? ______
D) Write the complete isotopic symbol for the element:
81.
Circle the one in each of the pairs of elements has the most neutrons.
A) 29
9
F or 21
10
Ne B) 42
20
Ca or
46
22
Ti
82.
In a nuclear reactor, an isotope of uranium, called U-235, is used. It has 92 protons and a mass number of 235.
A) What is the atomic number? ______

B) How many electrons are present? ______
C) How many neutrons are present? ______
D) Write the complete isotopic symbol for the element:
83.
Complete the following table for each of the isotopes listed:
18
8
O
-2 45
21
Sc
What is the atomic number?
What is the mass number?
How many protons?
How many neutrons?
How many electrons?
84
36
Kr
3
1
H
+1
84.
For each of the following pairs of elements, decide whether or not the pairs of elements are isotopes or completely different elements.
A) Element A has 22 protons and 24 neutrons. Element B has 22 protons and 25 neutrons. _______
B) Element C has 29 protons and 34 neutrons. Element D has 30 protons and 34 neutrons. ________
C) Element E has 24 protons and a mass of 50. Element F has the isotopic symbol
52
24
X . __________
E) Element G has an atomic number of 28 and a mass of 64. ______________________________
Element H has 30 protons and the symbol
64
30
X .
F) Element I is neutral and has 78 electrons and 117 neutrons. _______________________________
Element J has the isotopic symbol 196
78
X .
85.
A. An atom contains 15 protons, 16 neutrons and 15 electrons. Write the isotopic symbol: _________
B. Write the isotopic symbol for a possible isotope of this atom: ___________
C. If the atom gains three electrons, write the isotopic symbol for the ion: ___________

86.
Complete the following table:
Isotope
Symbol
Atomic
Name Number
Sodium-23
57
26
Fe
+2
27
32
Mass
Number
15
72
Protons
7
Neutrons
32
13
Electrons
10
10
Charge
0
+2
0
+3
19 20 18
51 23 0
87.
With the help of the periodic table, tell the number of protons, neutrons and electrons in each of the following isotopes:
A.
carbon-14
B.
cobalt-60
C.
bromine-81
D.
strontium-90 p: _______ n:_______ e: _______ p: _______ n:_______ e: _______ p: _______ n:_______ e: _______ p: _______ n:_______ e: _______
E.
27
13
Al
+3 p: _______ n:_______ e: _______
F.
84
36
Kr p: _______ n:_______ e: _______
G.
40
20
Ca
+2 p: _______ n:_______ e: _______
H.
4
2
He p: _______ n:_______ e: _______
88.
Write isotopic symbols for neutral atoms with:
A. 9 p+ and 10 n o
__________
B. 25 p+ and 30 n o
___________
89.
Which of the following atoms are isotopes?
C. 31 p+ and 39 n o
__________
D. 1 p+ and 0 n o
__________
A.
24
12
X B.
12
6
X C.
52
24
X D.
6
3
X E.
24
11
X F.
23
11
X

90.
Consult the periodic table and identify each of the elements listed in #89 above.
A. _______________ B. __________________ C. ___________________
D. _______________ E. __________________ F. ___________________
91.
A certain isotope of cobalt is five times as heavy as
12
6
C . What is the mass number of this isotope?
_____
92.
Choose the best answer from the choices given and circle its number.
A.
Neutral atoms have…
1) more negative charge than positive charge.
2) more positive charge than negative charge.
3) equal amounts of positive and negative charge.
4) variable charge.
B.
The particle having the greatest actual mass is the…
1) electron 2) neutron 3) neutrino 4) proton
C.
A particle that is present in every atom is the…
1) positron 2) proton 3) neutron
D.
The charge on the nucleus of an atom is due to…
1) neutrons 2) positrons 3) protons
4) neutrino
E.
All atoms of a given element have the same…
1) number of nucleons 3) number of neutrons
2) number of protons 4) mass number
4) electrons
F.
Which atomic particle would NOT be deflected by an electrical field?
1) neutron 2) alpha particle 3) beta particle
G.
The neutrons of an atom…
1) revolve around the nucleus 3) are positively charged
2) contribute to atomic mass 4) determine atomic number
H.
The subatomic particles which have equal but opposite charges are…
1) proton and electron 3) nucleus and neutron
4) electron and neutron 2) proton and neutron
I.
Which particle has the least mass?
1) proton 2) neutron 3) alpha particle
J.
A pure substance whose atoms all have the same atomic number is a(n)…
1) compound 2) element 3) radical
4) proton
4) electron
4) mixture
K.
Isotopes of an element have the same…
1) make-up of the nucleus
2) number of atoms
3) number of protons
4) number of neutrons

L.
An atom containing 9 protons, 10 neutrons and 9 electrons has a mass number of…
1) 9 2) 18 3) 19 4) 28
M.
As the number of neutrons in the nucleus of an atom increases, the atomic number of the element…
1) decreases 2) increases 3) remains the same
N.
As the atomic numbers of the elements increases, the number of protons in the nucleus
1) decreases 2) increases 3) remains the same
O.
The symbols 1
1
H ,
2
1
H , and 3
1
H show that the three kinds of hydrogen atoms have…
1) the same atomic mass
2) different atomic numbers
3) the same number of protons
4) the same number of neutrons
P.
The number of neutrons in the nucleus of a
3
1
H atom is…
1) 1 2) 2 3) 3 4) 4
Q.
As the atomic mass of chlorine isotopes increases, the number of protons…
1) decreases 2) increases 3) remains the same
R.
The number of protons in the nucleus of an oxygen atom is…
1) 8 2) 9 3) 20
S.
The number of neutrons in the nucleus of
37
17
Cl is…
4) 17
1) 17 2) 18 3) 20
T.
The atom whose nucleus contains the largest number of neutrons is…
1)
245
Am
95
2)
237
93
Np 3)
239
93
Np
4) 37
4)
239
92
U
U.
The symbol which shows phosphorus with a mass number of 31 is…
1)
15
31
P 2)
30
15
P 3)
16
15
P 4)
31
P
15
V.
What is the correct symbol for an element containing 6 protons and 8 neutrons…
1)
12
6
C 2)
14
6
C 3)
16
8
O 4)
14
8
O
W.
If an atom gains an electron, it becomes…
1) a cation 2) an anion
X.
A negative two (-2) charge indicates that the atom…
1) gained two electrons
2) lost two electrons
3) neutral
3) gained two protons
4) lost two protons

Average Atomic Mass: Use the concept of isotopes to explain why the atomic masses of elements
are not whole numbers.
___________________________________________________________________
Example: Use the following information to determine the atomic mass of chlorine. Two isotopes are known: chlorine-35 (mass = 35.0 amu) and chlorine-37 (mass = 37.0 amu). The relative abundances are
75.4% and 24.6%, respectively.
Solution: Recall that the text defines atomic mass as the weighted average of the masses of the isotopes of that element. To solve the problem:
Contribution of masses by each isotope = mass of isotope x relative abundance =
= 35.0 amu x
= 37.0 amu x
0.754 = 26.4 amu
0.246
The sum of the individual isotope mass contributions will equal the atomic mass.
= 9.10 amu
Problems :
26.4 amu + 9.10 amu = 35.5 amu
A.
Two isotopes are known: carbon-12 (mass = 12.00 amu) and carbon-13 (mass = 13.00 amu). Their relative abundances are 98.9% and 1.10% respectively. Determine the atomic mass of carbon.
B.
Given the relative abundance of the following naturally occurring isotopes of oxygen, calculate the average atomic mass of oxygen:
99.76% oxygen-16 0.037% oxygen-17 0.204% oxygen-18
C.
Determine the atomic mass of an element which has 2 isotopes with numbers of 6 (mass = 6.02) and 7
(mass = 7.02). The relative abundances are 7.42% and 92.6%, respectively.
D.
Calculate the average atomic mass of an element from isotope data. Element Y has 2 isotopes.
One has a mass number of 10, and a relative abundance of 20.%. The other isotope has a mass number of 11 and a relative abundance of 80.%.

Atoms of each element are ______________________ from the atoms of all other elements.
Dalton theorized that atoms are indivisible, but the discovery of _________________ particles changed his theory. We now know that atoms are made up of electrons, which have a _______________________ charge; __________________, which have a positive charge; and ___________________, which are neutral. The latter two particles are found in the _____________________ of the atom.
It was ______________________ who discovered the nucleus of the atom. The nucleus has a
____________________ charge and it occupies a very small volume of the atom. In contrast, the negatively charged __________________ occupy most of the volume of the atom.
The number of _________________________ in the nucleus of the atom is the atomic
____________________ of that element. Because atoms are electrically neutral, the number of protons and _____________________ in an atom are equal. The sum of the __________________ and neutrons is the mass number. Atoms of the same element are identical in some respects, but they can differ in the number of ________________ in the nucleus. Atoms that have the same number of protons but have different mass numbers are called _______________________.
The ______________________ of an element is the weighted average of the masses of the isotopes of that element. Two isotopes of sulfur are
32
16
S and
34
16
S . An atom of the sulfur-32 isotope contains _______________ protons and ______________ neutrons. The sulfur-34 isotope has
_______________ protons and ______________ neutrons.
Each of the three known isotopes of hydrogen has ________________ proton(s) in the nucleus.
The most common hydrogen isotope has ________________ neutrons. It has a mass number of
________________ amu and is called hydrogen-1.