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Chapter 4 Practice Problems Solutions
p. 111
15.
a.
b.
c.
d.
e.
f.
g.
h.
19
B
5
5
16
16
23
23
16.
a. 9 protons and 9 electrons
b. 20 protons and 20 electrons
c. 13 protons and 13 electrons
p. 112
17
a.
b.
c.
d.
e.
8
16
61
45
125
18.
a. 12C 6
b. 19 F9
c. 9Be4
p. 113
19.
16
O8 , 17O8, 18O8.
20.
Chromium- 50 has 26 neutrons, chromium – 52 has 28 neutrons, and
chromium – 53 has 29 neutrons.
p. 116
21.
Boron – 11
22.
Silicon- 28 must be by far the most abundant. The other two isotopes
must be present in very small amounts.
p. 117
23.
63.6 amu
24.
79.91 amu
Section Assessment 4.1
1.
As indivisible and indestructible.
2.
By using experimental methods.
3.
A scanning tunneling microscope.
4.
Answers should include the ideas that all matter is composed of
atoms, atoms of different elements differ, and chemical change
involves a rearrangement of atoms.
5.
Atoms of one element are never changed into atoms of another
element as a result of a chemical reaction.
6.
5 x 10-2 nm to 2 x 10-1 nm
7.
1.05 x 10-22 g
63.5 g = ? (6.02 x 1023 atoms)
Section Assessment 4.2
8.
Protons, neutrons, and electrons.
9.
A positively charged nucleus surrounded by electrons, which occupy
most of the volume.
10.
Proton, positive charge, relative mass = 1, electron, negative charge,
relative mass = 1/1840, neutron, no charge, relative mass = 1.
11.
Thomson passed an electric current through sealed glass tubes filled
with gases. The resulting glowing beam consisted of tiny negatively
charged particles moving at high speed. Thomson concluded that
electrons must be parts of the atoms of all elements. Millikan
determined the charge and mass of the electron.
12.
Rutherford expected all the alpha particles to pass straight through
with little deflection. He found that most alpha particles passes
straight through, but some particles were deflected at very large
angles and some even bounced straight back.
13.
The great majority of the alpha particles passed straight through the
gold foil.
14.
Rutherford’s atomic model describes the atom as having a positively
charged, dense nucleus that is tiny compared to the atom as a whole.
In Thomson’s plum pudding model, electrons were stuck in a chunk
of positive charge.
Section Assessment 4.3
25.
Atoms of different elements contain different numbers of protons.
26.
Mass number – atomic number = number of neutrons.
27.
They have different mass numbers and different numbers of neutrons.
28.
For each isotope, multiply its atomic mass by it % abundance, then
add the products.
29.
It allows you to compare the properties of the elements.
30.
Mass number 194 Pt 78.
31.
The atomic mass is the weighted average of the masses of its isotopes.
32.
33.
a. Lithium – 6
Lithium – 7
3 protons
3 protons
b. Calcium – 42
Calcium – 44
20 protons 20 electrons 22 neutrons
20 protons 20 electrons 24 neutrons
c. Selenium – 78
Selenium – 80
34 protons 34 electrons 44 neutrons
34 protons 34 electrons 46 neutrons
3 electrons 3 neutrons
3 electrons 4 neutrons
Any two; beryllium (Be), magnesium (Mg), strontium (Sr), barium
(Ba), radium (Ra).
End of Chapter 4 Assessment
34.
The smallest particle of an element that still has the properties of that
element.
35.
Democritus’ ideas were not helpful in explaining chemical behavior
because they lacked experimental support.
36.
Dalton would agree with all four-statement because they all fit his
atomic theory.
37.
The atoms are separated, joined, and rearranged.
38.
a. A beam of electrons (cathode rays) is deflected by an electric
field toward the positively charged plate.
b. The cathode rays were always composted of electrons
regardless of the metal used in the electrodes or the gas used in
the cathode ray tube.
39.
Repel.
40.
The mass of the proton and neutron are equals, protons are positively
charged and neutrons are neutral.
41.
Atoms are neutral: number of protons= number of electrons. Loss of
an electron means that the number of protons is greater than the
number of electrons, so the remaining particle is positively charged.
42.
The electrons were stuck in a lump of positive charge.
43.
Rutherford did not expect alpha particles to be deflected over a large
angle.
44.
Positive.
45.
Protons and neutrons.
46.
It has equal numbers of protons and electrons.
47.
The number of protons in the nucleus.
48.
a.
b.
c.
d.
e.
f.
49.
15
42
13
48
24
82
The atomic number is the number of protons. The mass number is the
sum of the protons and neutrons.
50.
Atomic
Number
Mass
Number
Number
Number
Symbol
of Protons of Neutrons of Element
9
19
9
10
F
14
29
14
15
Si
22
47
22
25
Ti
25
55
25
30
Mn
51.
Mass number, atomic masses, number of neutrons, relative
abundance.
52.
Because of the existence of isotopes.
53.
Which isotopes exist, their masses, and their natural percent
abundance.
54.
Average atomic mass is the arithmetic mean of the isotopes.
Weighted average atomic mass considers both the mass and the
relative abundance of the isotopes.
55.
The atomic mass is the weighted average of the masses of all the
isotopes.
56.
According to their atomic numbers.
57.
Sample answer: The table is set up so that chemical properties recur
at regular intervals.
58.
Very, very, tiny - but larger than protons and electrons.
59.
The nucleus is very small and very dense compared with the atom.
60.
5 protons and 6 neutrons in the nucleus, 5 electrons outside the
nucleus.
61.
All atoms of the same element are not identical (isotopes.). The atom
is not the smallest particle of matter.
62.
He used the quantity of charge value and the charge to mass ratio
measured by Thompson.
63.
They are the same value.
64.
The masses of isotopes in a sample of the element are average, based
on relative abundance. The result is the element’s atomic mass.
65.
207 amu
66.
No, in general he proposed a valid theory in line with the
experimental evidence available to him.
67.
Atoms are the smallest particle of an element that retains the
properties of that element.
68.
a. 92.9 % = 8289000/ 8922261
b. 99.89 % = 8912140/ 892261
c. 0.00993 % = 886/ 892261
69.
14
N7, 14.003 amu, 99.63 %, 15N7, 15.000 amu, 0.37 %, average atomic
mass = 14.01 amu.
70.
They were attracted to a positively charged plate.
71.
Atomic number is the same as the number of protons and electrons,
mass number minus atomic equals number of neutrons.
72.
Because they have identical numbers of protons, they also have
identical numbers of electrons; electrons are the subatomic particles
that are responsible for chemical behavior.
73.
The pattern repeats.
74.
a. The nucleus of an atom.
b. Very small volume, almost all the mass of the atom, high
density, positive charge.
c. Electron.
75.
Change the metal used as a target and account for differences in
deflection patterns.
76.
77.
The following are reasonable hypotheses. The space in an individual
atom is large relative to the volume of the atom, but very small
relative to an object the size of a hand. There are may layers of atoms
in a wall or a desk. The space that exists is distributed evenly
throughout the solid, similar to the distribution of air pockets in foam
insulation.
The theory must be modified and then retested.
78.
Yes, but answers will vary.
79.
In a chemical change, atoms are neither created not destroyed; instead
they are rearranged.
80.
Because diamond is denser than graphite, pressure could be used to
squeeze the carbon atoms closer together.
81.
92.5 % = x
6.941 = y (6.015) + x (7.016)
6.941 = (1-x)(6.015) + x (7.016)
82.
4 x 10-25 g
17(1.67 x 10-24) + 18 (1.67 x 10-24) =
5.845 x 10-23 g - 5.81 x 10-23 g = 3.5 x 10-25 g
83.
Pure chemistry involves the accumulation of scientific knowledge for
it so own sake; applied chemistry is accumulating knowledge to attain
a specific goal.
84.
Scientific theory attempts to explain why experiments give certain
results. Scientific law describes a natural phenomenon but does not
explain it.
85.
a.
b.
c.
d.
Element
Mixture
Mixture
Mixture
86.
48 g
87.
6.38 x 107 cm3
88.
99.5 g