Chemistry Reference
In-Depth Information
(d)
For 1 billion atoms of each:
3.68 (a)
Less than 1 amu is too small to be the mass of an atom.
(b)
12.0 g is much too large.
(c)
This again is much too large to be the mass of an atom.
(d)
More than 2000 amu is too large.
(e)
74.9 amu is the mass of an average arsenic atom.
65.4
10
9
amu
32.1
10
9
amu
2.04
(e)
For equal numbers of atoms, the ratio is always the same.
3.42
They occur in the same ratio in all naturally occurring
samples.
3.44
1.0 : 1.5
2:3
3.45
The weighted average is given by the sum of the fraction of
times its mass, the fraction of
3.69
Mass of selenium
mass of fluorine
x
amu
Number of selenium atoms
x
79
Number of fluorine atoms
x
19
4(
x
79)
There are four F atoms for every Se atom.
3.72
That fact was crucial because atomic numbers were as yet
unknown. Because atomic mass rises as atomic number
rises, and the periodic table is based on atomic numbers,
Mendeleyev could use atomic mass to build his table.
3.73
MgO
3.75
Each property of bromine may be expected to be an “average”
of those of chlorine and iodine. The actual properties are
Liquid under normal conditions
Dark brown
Reacts with metals
Reacts with oxygen
Does not conduct electricity
3.76
A crude periodic table could be built with the weighted aver-
age of the number of neutrons since the number of neutrons
rises generally as atomic number rises.
3.79
We can calculate the mass of each of the other elements per
gram of any one of them. For example, per gram of hydrogen,
the masses of carbon and oxygen are as follows:
28
Si
29
Si
times its mass, and the
30
Si
fraction of
times its mass:
(0.9221) (27.97693 amu)
(0.0470) (28.97649 amu)
(0.0309) (29.97376 amu)
Na
2
O
Al
2
O
3
SiO
2
P
2
O
3
SO
2
Cl
2
O
25.798 amu
1.36
2
amu
0.926
2
amu
28.09 amu
1
H
3.48
3.49 1.
Atoms of an element are the smallest particles with the
characteristic composition of the element.
2.
Atoms of an element have the same atomic number,
which is different from the atomic number of atoms of
any other element.
3.
Atoms of different elements can combine in certain small
whole-number ratios to form compounds.
3.53
Isotopic Atomic Mass No. of No. of No. of
Symbol Number Number Protons Neutrons Electrons
(a)
48 112 48 64 48
(b)
49 115 49 66 49
(c)
81 203 81 122 81
(d)
34 80 34 46 34
(e)
52 128 52 76 52
(f)
42 96 42 54 42
(g)
45 103 45 58 45
3.54 (a) (b) (c) (d) (e)
3.55 (a)
The atomic number and mass number are given. The
atomic number is implied by the symbol for the element.
(b)
Because the atomic number is the number of electrons for
a neutral atom, the two numbers are really only one value,
which would not yield the mass number or the number of
neutrons.
(c)
In a neutral atom, the numbers of protons and electrons
are the same, and again the number of neutrons and the
mass number could not be determined.
3.58 (a)
Hydrogen
(b)
3.60
The atomic mass of fluorine is 19.0 amu. The element with
atomic mass
11
48
Cd
62.1 g C
10.3 g H
6.03 g C
1 g H
27.6 g O
10.3 g H
2.68 g O
1 g H
11
49
In
(a)
20
81
Tl
52.2 g C
13.0 g H
4.02 g C
1 g H
34.8 g O
13.0 g H
2.68 g O
1 g H
8
34
Se
(b)
12
52
Te
The gram ratios can be simplified by dividing each set by the
second value in the set:
Ratios of Masses of Carbon Ratios of Masses of Oxygen
6.03 g : 4.02 g 2.68 g : 2.68 g
1.50 g : 1.00 g 1.00 g : 1.00 g
The numbers in the first set can be made integral by multiplying
each one by 2. The second set is 1 : 1.
9
42
Mo
103
45
Rh
3
H
2
H
1
H
3
He
3
H
3:2
1:1
The resulting values are integers within the accuracy of the
significant digits reported. If we chose to calculate the masses
per gram of carbon or per gram of oxygen, integral ratios
would have been obtained.
2
H
4
3
r
3
4
3
r
3
r
3
r
3
V
a
V
n
(10
4
)
3
10
12
3.80 (a)
10
19.0 amu
190 amu
is osmium (atomic
mass 190.2 amu).
3.62 (a)
If 37.4% weigh 185.0 lb, then
62.6% weigh 187.0 lb.
(b)
Yes. The atom has a volume 1000 billion times that of the
nucleus.
3.83
Per gram of hydrogen:
100.00%
37.4%
a
37.4
100
a
62.6
100
39.02 g S
2.44 g H
16.0 g S
1 g H
58.54 g O
2.44 g H
24.0 g O
1 g H
185.0 lb
b
187.0 lb
b
186 lb
Compound 1:
a
37.40
100
a
62.60
100
94.12 g S
5.88 g H
16.0 g S
1 g H
(b)
(184.953 amu)
b
(186.956 amu)
b
Compound 2:
186.2 amu
32.65 g S
2.04 g H
16.0 g S
1 g H
65.31 g O
2.04 g H
32.0 g O
1 g H
3.65
The
average
of the masses of lighter and heavier isotopes is
79.909 amu. (The actual composition is 50.54%
Compound 3:
79
Br
and
81
Br.)
49.46%
3.67
Atomic mass
For a fixed mass of hydrogen (1 g), the ratio of masses of sul-
fur is 1 : 1 : 1 and that of oxygen is
3.90 (a)
The oxygen in the nitrogen monoxide has a mass of
4.75 g
2.22 g
2.53 g O.
0.750 : 0 : 1
3 : 0 : 4
(0.7217) (84.9118 amu)
(0.2783) (86.9092 amu)
85.47 amu
