Name:
Pd:
Date:
Atoms Review: Answer on questions 1-10 on a separate sheet of paper. In answering the
questions, do you not copy directly from your notes. Answer in your own words.
1. What is the Law of Constant Composition?
2. Know the five points of Dalton’s Atomic Theory. Which of the points are no
longer accepted and why?
3. From J.J. Thomson’s experiment, what did he discover and how did he use it to
explain the structure of the atom?
4. Explain Ernest Rutherford’s gold-foil experiment. How did his experiment change
the model of the atom?
5. Who discovered the neutron and why was this an important piece for the model of
the atom?
6. Draw and label Neils Bohr’s model of the atom.
7. Briefly describe where electrons are located around the nucleus in the Wave
Mechanical Model.
8. What information do the atomic number and atomic mass for an atom provide?
9. What are isotopes? What notation is used to express isotopes? Use this notation to
express isotopes of chlorine-35, chlorine-36, and chlorine-37.
10. What is an ion and how is it formed from an atom? What is the difference
between a cation or anion?
11. In your own words, compare and contrast nuclear fission and fusion. Use
examples.
12. Fill in the table below using the information provided.
Isotope
Atomic
Atomic
Protons
Neutrons
Electrons
Number
Mass
Br
81
Fe
57
N
14
N
15
13.
Ion
Atomic
Number
Atomic
Mass
Protons
112
48
Neutrons
Electrons
Mg2+
S246
14
7
10
Atoms Review Answer Key
1. Law of Constant Composition, or Proust’s Law, states that a given compound will
contain the same proportion of elements by mass. In other words, for the
compound sodium chloride, NaCl, half of the mass of the compound will be due
to a sodium atom and the other half will be due to an atom of chloride. In water,
H2O, 2/3 of the mass will be due to hydrogen atoms and 1/3 is due to the mass of
an oxygen atom.
2. The points that are no longer accepted are:
-“all atoms of a given element are identical”  this is because of isotopes
(same atomic number, but different atomic mass)
- atoms cannot be created or destroyed because 
-nuclear fission (destroying atoms)
-nuclear fusion (creating atoms)
3. Thomson discovered electrons (negatively charged particles) using a cathode ray
tube. This changed the model of the atom because atoms now contained
negatively charged particles (electrons) inside a positively charged atom, like
chocolate chips (electrons) scattered in a ball of cookie dough (positive charge).
4. Gold foil experiment – alpha particles bombarded a piece of gold foil. Most of
these particles passed through the gold atoms, but several deflected due to a
dense, positively charged center. The atom, mostly made of empty space, now
included a nucleus with positively charged protons
5. James Chadwick discovered the neutron and it accounted for the remaining mass
of the atom (atomic mass).
6.
7. Electron location is defined in terms of probability in the Wave Mechanical
model. That is, instead of electrons orbiting around the nucleus, electrons move
around in a 3-dimensional space called an electron cloud or orbital. The more
dense the electron cloud or orbit is of electrons, the higher probability finding an
electron within that area.
8. Atomic number = number of protons; atomic mass = sum of protons and neutrons
9. Isotopes are atoms that contains the same number of protons, but have a different
number of neutrons, thereby changing the atomic mass. Isotopes can be expressed
in AZX notation, where “A” is the atomic mass, “Z” is the atomic number, and
“X” is the element symbol for the atom.
10. An ion is an atom that contains a charge. This occurs when that atom has lost its
electrons or has gained electrons from another atom. A cation is an ion that has
lost electrons, therefore making it positively charged. An anion is an ion that has
gained electrons, therefore making is negatively charged.
11. Nuclear fission occurs when one large, heavy atom is split into two smaller atoms
and neutrons and energy are released. Nuclear fusion occurs when two smaller,
lighter atoms combine with enough energy to form one new atom releasing a
neutron and energy.
12. Answers in red
Isotope
Atomic
Atomic
Protons
Neutrons
Electrons
Number
Mass
Br
35
81
35
46
35
Fe
26
57
26
31
26
N
7
14
7
7
7
N
7
15
7
8
7
13. Answers in red
Ion
Atomic
Number
Atomic
Mass
Protons
Neutrons
Electrons
Mg2+
12
24
12
12
10
S2-
16
32
16
16
18
Cd2+
48
112
48
64
46
N3-
7
14
7
7
10