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Arnoldi
Honors Chemistry
Atomic Theory One
Review Key
1. Definitions
a. Atoms
the smallest piece of an element that still retains the properties of that element
b. Atomic Number
# of protons in the nucleus
c. Mass Number
the sum of the protons and neutrons in the nucleus this is for one
particular isotope
d. Nucleons
particles that make up the nucleus (neutron and proton)
e. anion
negatively charged particle
f. cation
positively charged particle
g. ion
any charged particle
h. isotopes
atoms of the same element with different masses
i. Quantum
an exact amount of energy
j. Quanta
plural of quantum
k. Photon
light energy
l. Radioactivity
Spontaneous disintegration in which small particles of matter (alpha or
beta particles) and /or electromagnetic radiation (gamma rays) are
emitted by unstable atomic nuclei
m. Electromagnetic Radiation
n. Half-Life
a form of energy that exhibits wavelike behavior as it travels
through space
the time it takes for a sample of radioactive matter to decay to half its original size
2. How do we see individual atoms? use a scanning tunneling microscope
3. Which of the following appear on the periodic table?
Atomic Number
Atomic Mass
4. What controls the identity of the atom?
Mass Number
atomic number (number of protons)
5. Subatomic Particles:
Particle
Charge
Location in Atom
In Nucleus
+
Mass (Two Ways)
1 amu
1.67 X 10-24 grams
Proton
Electron
-
Negligible
(so small as to be insignificant)
In Orbitals
(outside of nucleus)
Neutron
neutral
1 amu
(atomic mass unit)
In Nucleus
6. What controls the charge of the particle? Electrons
7. How do we form cations?
Lose electrons
8. How do we form anions? Gain electrons
9. Describe Quarks
Quarks make up protons and neutrons.
There are six types of quarks, (up, down, beauty, truth, charmed, strangeness)
10. Why do isotopes have different masses? They have different numbers of neutrons.
11. What are the three isotopes of hydrogen? Protium, deuterium, tritium
12. Fill in the following table:
Isotope
41
Ca+2
4
He
16
O-2
235
U
P-3
Protons
Electrons
Neutrons
20
18
21
2
2
2
8
10
8
92
92
143
15
18
16
13. Compare Continuous and Discontinuous matter theories.
Matter is one continuous piece, or matter can be broken down into smaller pieces.
(You can only buy a whole sub, or you can buy a slice of pie).
14. Fill in the Blanks
Democritus was a Greek philosopher who first used the term “atom”, which means indivisible.
He thought atoms were tiny and indestructible. He created the Discontinous theory of matter,
which stated that matter is not one continuous piece.
15. Fill in the Blanks
In the 18th century, we had the first experimental evidence that could support the idea of
an atom.
Antoine Lavoisier discussed the Law of Conservation of Mass, and Joseph Proust
discussed the Law of Definite Proportions, which states that a chemical compound contains the
elements in exactly the same proportions by mass, regardless of the size of the sample or source of
the compound.
16. Fill in the Blanks
John Dalton discussed the Law of Multiple Proportions which stated that if two or more
different compounds are composed of the same two elements, then the ratio of the masses of the
second element, combined with a certain mass of the first element, is always a ratio of small whole
numbers. Dalton stated four thoughts about atomic theory: (1) All matter is made up of atoms
which are indivisible and indestructible, (2) Atoms of the same element are identical – in particular
their masses are the same, (3) Atoms of different elements are completely different, in particular
their masses are different, and (4)
compounds.
Atoms combine in simple whole number ratios to form
(They due this via chemical reactions which are the result of the separating or
combining of atoms. Dalton’s atomic model was a Billiard Ball.
17. Fill in the Blanks
Today, we agree that matter is made of atoms, atoms do combine in simple whole number
ratios, and chemical reactions are the result of the separating /combining of atoms.
18. Fill in the Blanks
However, we disagree with some of Dalton’s ideas, because we know that atoms are divisible
into subatomic particles, and atoms are destructible via nuclear reactions (we can create atoms in
nuclear reactions, also). Also, atoms of different elements can have the same mass, and atoms of
the same element can have different masses because of isotopes.
19. Fill in the Blanks
A guy named William Crookes had the next impact on atomic theory. Crooke’s studied the
behavior of gases in vacuum tubes (aka cathode ray tubes), which were the forerunners of picture
tubes in television. Crookes theorized that some kind of radiation or particles was traveling from
the cathode across the tube. He called this radiation cathode rays. Draw a cathode ray tube
below. Label the + and - charges, the cathode ray, and the cathode and anode
cathode ray (must start at the cathode and move toward the anode)
20. Fill in the Blanks
J.J. Thomson used Crookes tube to discover the electron. He determined that the electron
had a negative charge by bending the ray in the Cathode Ray tube using + and – fields. The ray bent
toward the positive field. The ray bent away from the negative field. From this data, and knowing
that likes repel and opposites attract, Thomson decided that since the ray is attracted to the
positive field, and repelled by the negative field, it must be negative. Thus, he determined that the
cathode ray is a stream of negatively charged which he called electrons. His atomic model was
called the Plum Pudding model.
21. Fill in the Blanks
Thomson and Milliken worked together on the Oil Drop Experiment in which they discovered
the mass of the electron to be 9.11 X 10-28 grams which is nearly negligible. This can also be
expressed as 1/1837 amu. (protons and neutrons have a mass of 1 amu). They also determined that
the charge is 1.602X10-19 coulomb which this is the smallest charge ever detected.
22. Fill in the Blanks
The next major contributor to Atomic Theory was Eugene Goldstein who in 1886 found
evidence for the proton.
23. Fill in the Blanks
Rutherford used the Gold Foil Experiment to discover the atom’s nucleus. Give a basic
rendering of this experiment below. Rutherford bombarded gold foil with alpha particles which are
positively charged Helium atoms. He saw that most of the particles went through, but a few were
deflected. Since alpha particles are positive, they must have hit something positive inside of the
atom (likes repel).
From these results, Rutherford concluded that there is a small, dense,
positively charged center in the atom, which he called the nucleus. He also concluded that the atom
is mostly empty space, and that the bulk of the mass of the atom is in the center. Rutherford knew
that the electrons where outside the nucleus, occupying most of the volume of the atom. However,
he couldn’t explain why, if electrons are negative, and the center of the atom is positive, they
weren’t attracted to the center of the atom.
alpha particles
deflection
most go through
24. Fill in the Blanks
James Chadwick confirmed the existence of the neutron by bombarding beryllium atoms
with alpha particles via the following equation:
4
9
He
+
2
12
Be
1
C
4
+
n
0
6
25. Fill in the Blanks
Niels Bohr said that electrons reside in energy levels, aka energy shells. The energy of the
level increases as the distance from the nucleus increases, and electrons fill the energy levels from
the inside out, or from low to high energy. Atoms can be found in the ground state or the excited
state. A ground state atom will fill the first shell before moving to the second, the second before
moving to the third, etc. The last shell (the outermost shell) may or may not be filled. This is the
lowest possible energy state.
An excited state atom has an inside shell that is NOT filled before
moving to the next shell. It is NOT in the lowest possible energy state. Another name for the
ground state is the stable state. Another name for the excited state is the unstable state. To
move from one shell to another, or to move from one energy level to another, you must gain or lose
the exact amount of energy between those two levels.
26. Draw a Bohr Diagram for each of the following:
a. Lithium Atom
3p
) 2e-
)1e-
b. Phosphorus Ion
15 p
)2e-
)8e-
)8e-
c. Potassium Ion
19 p
)2e-
)8e-
)8e-
27. What is an alpha particle? a positive helium atom
Complete the following alpha particle radiation equation below:
4
He
2
+
9
Be
4

12
C
6
1
+
n
0
28. What is a beta particle?
an electron
Complete the following beta particle radiation equation below:
234
Th 
90
29. What is a Gamma Ray?
234
Pa
91
0
e
-1
high energy electromagnetic radiation
30. The half-life of iodine-131 is 8 days. What mass of this isotope remains from a 4.00 g sample
after 32 days?
forward in time, divide by 2
Amount
4.00g
2.00g
1.00g
0.50g
Time
0 days
8 days
16 days
24 days
0.25g
32 days
forward in time, add half life
31. The starting mass of a radioactive isotope was 20.0g. Its half-life is two days. The mass is now
2.5g. How old is the sample?
forward in time, divide by 2
Amount
20.0g
10.0g
5.0 g
2.5 g
Time
0 days
2 days
4 days
6 days
forward in time, add half-life
32. A sample of radioactive matter has a mass of 10.5g. It is 24 hours old, and its half-life is 6
hours. What was the original mass of the sample?
back in time, multiply by 2
Amount
10.5 g
21.0g
42.0g
84.0g
168 g
Time
0 hours
6 hrs ago
12 hrs ago
18 hrs ago
24 hrs ago
back in time, add half-life “ago”
PROBLEMS
12
1. What is the atomic mass for element B?
13
B = 82.20%
B = 17.80 %
(12.008 u) (82.20) + (13.092u) (17.80) =
100
12.008 amu
13.092 amu
12.201 amu
2. Find the %’s of 2 isotopes of element X given the following information:
average atomic mass = 4.1989
isotope 1 = 4X
isotope 2 = 5X
[(4amu)(x)] + [(5amu)(100-x)]
100
4x + 500 - 5x
-1x
= 4.1989 amu
= (4.1989) 100
= -80.11
x
100 – x
= 80.11 %
= 19.89%
3. Element Q consists of two naturally occurring isotopes: Isotope One’s abundance is 43.55 % and
its mass is 40.009 amu. If the average atomic mass of the element is 41.956 amu, what is the
percent abundance and exact mass of the other isotope?
Percent Abundance
100 – 3.55 = 56.45%
Mass of Second Isotope
[(40.009 amu)(43.55)] + [(x amu)(56.45)]
100
1742039195 u +
=
41.956 amu
56.45X
=
4195.6 amu
56.45 X
=
2453.20805
x
=
43.458 u