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First Semester Exam Essays (2012)
Essay
Directions: Write out your responds ahead of time. Submit your responses before the exam starts on
the exam day. You will NOT have the opportunity to respond during the exam period.
1. Compare and contrast solids, liquids, gases, and
plasma by explaining the behavior of their
particles. Draw models to illustrate your answer.
7. What can you determine about the atomic
structure of an element if you know the atomic
number of the element and mass numbers of its
isotopes? What additional information is needed
to determine the average atomic mass of the
element? How do you determine the average
atomic mass of the element?
2. Use examples to show how the properties and
classifications of elements change as you move
across a period of the periodic table.
8. Explain the significance of Avogadro's constant,
6.022 × 102 3. What is the relationship between it
and the molar mass of oxygen, 16.00 g/mol?
3. Using the two models shown below explain how
each model resembles the object it represents.
Explain how each model differs from the object it
represents.
9. Elements of the fourth period fill the 4s sublevel
with electrons before filling the 3d sublevels.
Also, some elements move an electron from a
filled 4s sublevel to an unoccupied 3d sublevel.
Explain these behaviors.
10. Explain nuclear charge and how it affects the
general trend in radii of atoms of elements going
from left to right across a period in the periodic
table.
4. The table below show measurements made on
samples of three unknown materials. Explain how
this data could be used to identify the three
materials.
11. Compare and contrast ionic and covalent
bonding.
Mass and Volume Data
Material
Mass (g)
Volume (mL)
1
6.02
2.23
2
18.42
2.34
3
35.15
3.10
5. Explain what is meant by the law of definite
proportions, the law of conservation of mass, and
the law of multiple proportions.
6. Why do scientists use Dalton's theory, even
though parts of it have been proven wrong? How
much of Dalton's theory do scientists still accept?
1
ID: A
First Semester Exam Essays (2012)
Answer Section
ESSAY
1. ANS:
The arrangement of the particles in the three states accounts for their different properties. Particles in a solid
move very little; particles in a liquid move more; and gas particles and plasma particles move the most. In
drawn models, particles in solids should be closely packed and structured; particles in liquids should appear able
to flow randomly past one another; and particles in gases should appear sparsely and randomly spaced. Plasma
particles should have lost some of their electrons.
PTS: 1
DIF: III
REF: 2
OBJ: 3
STA: SC.A.1.4.3
2. ANS:
The closer two elements are within a period, the more similar their properties are. Moving across a period,
elements progress from metals to metalloids, to nonmetals, to noble gases.
PTS: 1
DIF: III
REF: 3
OBJ: 3
STA: SC.A.2.4.5
3. ANS:
The model of the sun is accurate in showing that the sun is round and has a fiery surface. The model of an
atom shows that the atom is a particle.
The sun model is inaccurate because it is only two-dimensional, and it is smaller than the real sun. In addition,
it does not show the sun's composition. The atomic model is inaccurate because it is larger than a real atom,
because it is only two-dimensional, and because it does not depict the atom's composition and chemical
properties.
PTS: 1
DIF: III
REF: 1
OBJ: 3
STA: SC.H.2.4.1
4. ANS:
The density of each sample could be calculated. Then each value could be compared to known values to
identify the substances.
PTS: 1
DIF: III
REF: 2
OBJ: 4
STA: SC.H.2.4.1
5. ANS:
Definite proportions: regardless of the origin or size of samples of a particular compound, their elements are
always in the same proportion. Conservation of mass: the mass of the elements combined in a compound is
the same as the sum of the masses of the individual elements. Multiple proportions: when two elements
combine to form two different compounds, the ratio of the masses of one element that combine with a fixed
mass of the other element is a small whole number.
PTS: 1
STA: SC.B.1.4.2
DIF: III
REF: 1
OBJ: 1
1
ID: A
6. ANS:
Dalton's theory led to the modern theory of the atom. Although scientists now know that atoms can be
divided and that elements exist as isotopes, most of his early theory is still accepted.
PTS: 1
DIF: II
REF: 1
OBJ: 3
STA: SC.B.1.4.2
7. ANS:
The atomic number equals the number of protons in the nucleus of an atom and also equals the number of
electrons in the neutral atom. The mass number is the sum of the number of protons and neutrons and can be
used, with the atomic number, to find the number of neutrons in each isotope. Each isotope of the element
has a different mass number but the same atomic number as the element.
In order to determine the average atomic mass of the element, you needed to know the relative
abundance and the exact mass of each isotope. Then, multiply the relative abundance (in decimal form) times
the atomic mass for each isotope, and adding the results.
PTS: 1
DIF: II
REF: 3
OBJ: 2
STA: SC.A.2.4.3
8. ANS:
Avogadro's constant is the number of particles in 1 mol of a substance. Because the molar mass of oxygen
atoms is 16.00 g/mol, the mass of 1 mol, or 6.022 × 102 3, oxygen atoms is 16.00 g.
PTS: 1
DIF: II
REF: 3
OBJ: 4
STA: SC.H.2.4.1
9. ANS:
Elements fill the 4s sublevel with electrons before filling the 3d sublevels because the 4s sublevel is lower in
energy than the 3d sublevels. According to the Aufbau principle, an electron occupies the lowest energy level
that can receive it. Some elements move an electron from a filled 4s sublevel to an unoccupied 3d sublevel so
they can have more unpaired electrons in their configuration. This minimizes electron repulsions and is
therefore a more stable arrangement.
PTS: 1
DIF: III
REF: 3
OBJ: 2
10. ANS:
Nuclear charge is the attraction an atomic nucleus has on the electrons surrounding it. As you move from left
to right across a period, the atomic number increases, and therefore the number of protons in the nucleus
increases. The more protons within a nucleus, the greater is the nuclear charge. A greater nuclear charge pulls
the electrons closer to the nucleus, decreasing the atomic radius.
PTS: 1
STA: SC.A.1.4.2
11. ANS:
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DIF: II
REF: 3
OBJ: 2
PTS: 1
STA: SC.A.1.4.5
DIF: II
REF: 2
OBJ: 5
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