Answers To Composition Of Atoms: The Sub-Atomic Particles
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4Answers to Composition of Atoms: The Sub-atomic Particles
1. Write complete definitions for each of the following terms. Include one additional piece of information
such as an example or application:
a) Atomic number: the number of protons in the nucleus of an atom. This determines what type of atom
(element) it is. The symbol for atomic number is Z.
b) Mass number: this is the sum of the number of protons and the number of neutrons in the nucleus of
an atom. This determines how much the atom weighs. Mass number is a counted value, it has no units.
The symbol for mass number is A.
c) Isotope: Isotopes are atoms of the same element that have different numbers of neutrons, so some
atoms of an element are heavier than others. That is, isotopes have the same atomic number but
different mass numbers. All isotopes of an element have the same chemical properties. Isotopes are
identified using a standard format such as “Zn – 65”, where 65 is the mass number of the isotope.
d) Ion: an ion is a charged atom. It is charged because the number of electrons does not equal the number
of protons. If there are more electrons than protons, the ion will have a negative charge. If there are
fewer electrons than protons, the ion will have a positive charge.
2. Complete the following chart:
Element
Atomic #
# of Protons
# of Electrons
Overall
# of Neutrons
Mass
Charge
Number
He
2
2
2
0
2
4
Al
13
13
10
+3
14
27
Ca
20
20
18
+2
20
40
Ni – 58
28
28
26
+2
30
58
Sr
38
38
36
+2
52
90
V
23
23
23
0
28
51
Ag – 107
47
47
46
+1
60
107
I
53
53
54
-1
74
127
Yb
70
70
67
+3
103
173
Au
79
79
79
0
118
197
Au
79
79
76
+3
118
197
U
92
92
92
0
143
235
U
92
92
92
0
146
238
H – 1
1
1
0
+1
0
1
Ni
28
28
25
+3
31
59
P
15
15
18
-3
16
31
Zn - 65
30
30
28
+2
35
65
Si - 28
14
14
18
-4
14
28
3. Do ALL atoms (or ions) contain protons?
•
all atoms must contain protons (or they wouldn’t be atoms)
•
all atoms do not contain electrons eg. the hydrogen ion (H+) has no electron, and an alpha particle
2+
(He
) is a helium nucleus without any electrons
•
all atoms do not contain neutrons eg. most hydrogen atoms (H-1) do not have neutrons
4. Using the standard format (eg. “Ag-107”), identify any isotopes from the above table:
•
Ni – 58 and Ni – 59 are isotopes (they are also two different ions of nickel)
•
U – 235 and U – 238 are isotopes of uranium
•
the atoms of gold (Au) are NOT isotopes, because both atoms have the same mass number
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