Honors Chemistry
Unit 2 Sample Problems
Answers to selected problems
1. The earliest mention of the atom as a
fundamental particle of matter is from
c. Democritus.
2. ____________ was one of the first
philosophers to believe that matter was
composed of atoms.
c. Democritus.
3. Two isotopes of an element have
different numbers of
d. neutrons.
4. Two different atoms of an element that
have different numbers of neutrons are
called
d. isotopes.
5. Dalton felt that atoms were
a. were tiny indivisible particles.
6. Who was the first person to use
experimental methods to form a
scientific theory of atoms?
b. Dalton
7. Thomson used ____________ to
discover the electron?
b. a cathode ray tube
8. Which investigator used alpha
particles to determine that the nucleus
of the atom is a small sphere at the
center of an atom?
a. Rutherford
9. Who discovered the neutron?
c. Chadwick
10. Thomson used a cathode ray tube to
discover the
b. electron.
11. Rutherford used alpha particles to
determine that the nucleus
____________ at the center of the
atom.
a. is a small sphere
Page 1 of 4
12. If electrons in an atom have the lowest
possible energies, the atom is in the
_______ state.
d. ground
13. If one or more electrons in an atom
have energies higher than the lowest
possible energies, the atom is in the
_______ state.
b. excited
14. The part of the atom where the
electrons CANNOT be found is the
d. nucleus.
15. The region outside the nucleus where
an electron can most probably be
found is the
a. electron cloud.
16. Quantum numbers are sets of numbers
that describe the properties of
c. atomic orbitals.
17. Atomic orbitals are described by sets
of numbers called
c. quantum numbers.
18. The set of orbitals that are dumbbellshaped and directed along the x, y, and
z axes are called
a. p orbitals.
19. The set of orbitals that are sphericallyshaped are called
b. s orbitals.
20. The noble gas electron-configuration
notation for 83Bi is
a. [Xe] 6s24f145d106p3.
21. What is the complete electron
configurations of sodium, 11Na?
d. 1s2 2s2 2p6 3s1
22. The noble gas electron-configuration
notation for 33As is
a. [Ar] 4s23d104p3.
Honors Chemistry
Unit 2 Sample Problems
Answers to selected problems
23. What is the complete electron
configurations of magnesium, 12Mg?
c. 1s2 2s2 2p6 3s2
electron in
excited state
25.
ΔE
photon in
Ephoton
nucleus
atomic
orbitals
electron in
ground state
electron in
excited state
26.
ΔE
photon out
Ephoton
atomic
orbitals
nucleus
Page 2 of 4
24. Which of the following atomic
symbols is correct?
a. 146C
An electron starts in a low lying atomic orbital,
the ground state. When a photon of exactly the
right energy interacts with the atom, the electron
is promoted to a higher energy level (a more
distant atomic orbital) putting the electron into
an excited state. The energy of the photon must
be exactly the same as difference in energy
between the orbitals, Ephoton = ΔE.
An electron starts in a high energy atomic
orbital,the excited state. When the electron
back to the lowest available atomic orbital, the
the ground state, a photon is emitted by the
atom. The energy of the photon must be
exactly the same as difference in energy
between the orbitals, Ephoton = ΔE.
electron in
ground state
27. J. J. Thomson noted that, if he
placed a magnet in the vicinity of
the beam in the cathode ray tube,
the beam was deflected in such a
way that it had to be composed
of negatively charged particles.
This occurred no matter what
material was used as the cathode.
This led Thomson to conclude
that all atoms contained small, negatively charged particles.
28.
Lead with radioactive source
Stream of alpha
particles
Thin gold foil
ZnS coated screen
Rutherford shot a stream of
alpha particles toward a thin
gold foil. He expected that
most of the particles would
pass directly through the foil.
Most of them did, but some of
the particles were deflected at
very large angles. This meant
that the positive charge in the
atom was concentrated in a
very small volume.
Honors Chemistry
Unit 2 Sample Problems
Answers to selected problems
Page 3 of 4
29. When blue light or ultraviolet light is shined on a
light
metal surface, electrons are released from the surface.
Red light does not release any electrons from the
surface. This is called the photoelectric effect. Einstein
metal surface
said that the energy of photons (blue photons have
more energy than red photons) is what caused the
release of the electrons. He was using the idea of light as a particle rather than the
idea of light as a wave. This was the first demonstration of the wave-particle duality of
light and matter.
30. The Schrödinger equation is used for determining the possible locations of an electron
in an atom. The equation gives a probability of a volume that the electron will be
restricted to and this probability leads us to the idea of an electron cloud.
31. Heisenberg’s Uncertainty Principle says that we cannot, simultaneously know the
exact location and speed of an electron in an atom. It puts a limit on the level of
knowledge we can have about the structure of individual atoms.
32. Answer: Average Atomic Mass = 114.9 ± 0.2
33. Answer: Average Atomic Mass = 221.5 ± 0.2
34. Answer: Average Atomic Mass = 36.71 ± 0.02
35.
a.
b.
c.
d.
e.
f.
g.
30Zn:
a.
c.
e.
g.
29Cu:
36.
37. a.
d.
g.
1s2 2s2 2p6 3s2 3p6 4s2 3d10
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d6
1s2 2s2 2p6 3s2 3p6
1s2 2s2
1s2 2s2 2p4
37Rb:
35Br:
44Ru:
18Ar:
4Be:
8O:
17Cl:
36Kr:
14Si:
3d
4s
3p
3s
2p
2s
1s

4d
5s
[Kr]

28Ni:
45Rh:
50Sn:
5p
4d
5s
[Kr]
[Ar] 4s2 3d9
[Ne] 3s2 3p5
[Ar] 4s2 3d10 4p6
[Ne] 3s2 3p2




b.
b.
d.
f.
11Na:










3s
2p
2s
1s
41Nb:
12Mg:
[Xe] 6s1
[Kr] 5s2 4d3
[Ne] 3s2
c.


56Cs:

2p
2s
1s

5s
[Kr]

9F:


















e.
54Xe:
5p
4d
5s
[Kr]
f.





38Sr:


Honors Chemistry
Unit 2 Sample Problems
Answers to selected problems
Page 4 of 4
38. a. Democritus proposed the first atomic theory about 2500 BC. He did not have any
evidence to support his proposal.
b. John Dalton proposed the first atomic theory based on experimental evidence in the
early 1800’s.
c. J. J. Thomson discovered the electron and showed that the atom was not just a solid,
indestructible particle, but that it had internal parts. He developed the “Plum Pudding
Model” of the atom.
d. Ernest Rutherford determined that the positive charge in the atom resided in a small
volume at the very center of the atom. He developed the “Solar System Model” of the
atom.
e. Niels Bohr used atomic line spectra to show that the electrons in atoms are restricted to
specific orbitals at set energies (distances) from the nucleus.
f. James Chadwick discovered the final piece of the nucleus – the neutron. This
explained the variation in the mass of different atoms of the same element.
g. Max Planck theorized that light could be thought of as particles (photons or packets of
energy) with specific amounts of energy associated with the color of the light.
h. Albert Einstein explained the “photoelectric effect” by using Planck’s model of
photons, showing that light could be thought of as either a particle or as a wave.
i. Erwin Schrödinger developed an equation that could predict the position of an electron
in an atom. The position was expressed in the form of a probability and led to the idea
of an electron cloud.
j. Werner Heisenberg developed the idea that we cannot determine the speed and position
of a sub-atomic particle with accuracy. This is called the Heisenberg Uncertainty
Principle.
39. Write the name and determine the number of protons, neutrons, and electrons in each of the
following neutral atoms.
atom
name
protons
neutrons
electrons
𝟒
𝟐𝐇𝐞
helium
2
2
2
𝟓𝟔
𝟐𝟔𝐅𝐞
iron
26
30
26
𝟒𝟎
𝟐𝟎𝐂𝐚
calcium
20
20
20
𝟐𝟎𝟏
𝟖𝟎𝐇𝐠
mercury
80
121
80
𝟑𝟏
𝟏𝟓𝐏
phosphorus
15
16
15
𝟏𝟒
𝟔𝐂
carbon
6
8
6
𝟏𝟑𝟏
𝟓𝟒𝐗𝐞
xenon
54
77
54
𝟏𝟗
𝟗𝐅
fluorine
9
10
9