Chemistry Reference
In-Depth Information
20
10
0
40
18
+
40
2+
32
16
2-
Ne
Ag
Ca
S
Number of protons
10
18
20
16
Number of electrons
10
17
18
18
Number of neutrons
10
22
20
16
Notice that it is possible for atoms of two different elements to have
the same number of electrons. They can also have the same number of
neutrons, but two atoms of different elements cannot have the same num-
ber of protons. As I said earlier, it is the number of protons that deter-
mines the identity of an element.
Now, let's look at elemental notations for the three isotopes of hydrogen.
Notice that the three isotopes of hy-
drogen have the same atomic number
but different mass numbers. This is be-
cause they have the same number of pro-
tons but a different number of neutrons.
If you change the number of protons, you
change the identity of the element.
Let's try some practice questions.
Elemental Notation for the
Three Isotopes of Hydrogen
H
H
H
1
1
2
1
3
1
Protium
Deuterium
Tritium
Figure 3-2d
Lesson 3 - 2 Review
1.
Determine the number of protons shown in each of the following
elemental notations.
a)
39
19
56
26
2+
22
11
88
38
2+
4
Fe
Sr
K
b)
c)
Na
d)
2.
Determine the number of neutrons shown in each of the following
elemental notations.
a)
27
13
24
12
2+
5
86
37
31
16
2-
b)
Mg
c)
d)
S
Al
Rb
3.
Determine the number of electrons shown in each of the following
elemental notations.
a)
137
56
55
25
14
7
3-
7
3
+
b)
c)
N
d)
Li
Ba
Mn
4.
Which of the following atoms has an equal number of protons and
neutrons?
a)
27
13
55
25
39
19
22
11
Al
b)
Mn
c)
K
d)
Na
5.
Which of the following would represent different isotopes of the
same element?
a)
12
6
12
7
12
6
13
7
12
6
12
6
12
6
14
6
b)
c)
d)
X
and
X
X
and
X
X
and
X
X
and
X
