ISOTOPIC NOTATION
isotopes are atoms with the same number of
protons but different number of neutrons
A
Z
X
A = mass number
(the total number of protons + neutrons)
Z = atomic number
(the total number of protons)
X = element symbol
READING ISOTOPIC NOTATION
46
21
Sc
46 = mass number
(the total number of protons (21) + neutrons
(25)
21 = atomic number
(the total number of protons (21))
Sc = element symbol
In a neutral atom, the number of electrons
PRACTICE PROBLEMS
15N
7
8
7
# protons = ____
# neutrons= ____
#electrons = ___
35P
15
# p = ____
20
# n= ____
15
#e- = ___
33
# n= ____
27
#e- = ___
62Cu2+
29
# p = ____
76Se3-
# p = 34
____
42
# n= ____
37
#e- = ___
Writing ISOTOPIC NOTATION
1. Write the symbol for the atom with an atomic
number of 21 and a mass number of 48.
48
Sc
2. Give the complete chemical notation for the
nuclide with 23 protons, 26 neutrons and 20
electrons.
49V3+
3. Write the isotopic notation for
110Pd
a. Z = 46
A = 110
b. An atom containing 24 protons, 28 neutrons,
and 21 electrons
52Cr3+
c. Titanium-50 50Ti
PRACTICE PROBLEMS
1.
Pt4+
118
78 # n = _____
# p = _____
196
196
mass number = ________
195.1 amu
atomic mass = ________
74
#e- = _____
78
atomic number = _______
platinum
name of element = _______
2. Indicate the appropriate atomic mass of an element with
30 protons, 30 neutrons, and 28 electrons.
65.39 amu
Atomic Mass
• The atomic mass of an element represents the
average mass of all the isotopes found in nature. No
element exists with only one possible isotope.
Hydrogen has the smallest number of isotopes: 1H
protium, 2H deuterium, 3H tritium. Its atomic mass
is 1.0079 amu (atomic mass units). The atomic mass
is calculated by adding the % of 1H mass found in
nature to the % of 2H mass found in nature plus the
% of 3H mass.
• % 1H + % 2H + % 3H = average mass (atomic mass)
• Generally the formula used is:
% X + % Y + % Z… = atomic mass.
An instrument called the mass spectrometer is generally
used to determine the percentages and individual
masses of each isotope.
Atomic Mass
• Silver is found to have two stable isotopes, one has an atomic
mass of 106.904 amu and the other weighs 108.905 amu. The
first isotope represents 51.82 % of the mass of the element and
the second represents 48.18 %. What is the atomic mass of the
element silver?
The equation to use is %X + % Y = average
And remember to turn your percents into fractions before
multiplying.
(0.5182) 106.904 amu + (0.4818) 108.905 amu =?
55.398 amu + 52.470 amu =?
107.868 amu !!
Now look at the periodic table to verify the answer.
PRACTICE PROBLEMS # 8
1. A sample of neon contains three isotopes, neon-20
(with an isotopic mass of 19.9924 amu), neon-21
(20.9939 amu) and neon-22 (21.9914 amu). The natural
abundances of these isotopes are 90.92%, 0.257 %, and
8.82 %. Calculate the atomic weight of neon.
20.17 amu
2. There are only two naturally occuring isotopes of
copper, 63Cu and 65Cu. Copper has an atomic mass of
63.55 amu. What is the natural abundance of each
65Cu = 30% & 63Cu = 70%
isotope?
3. There are only two naturally occuring isotopes of
gallium, 69Ga and 71Ga. What is the natural abundance
of each isotope?
69Ga = 60% and 71Ga = 40%
GROUP STUDY PROBLEM #8
_______1. The element with atomic number 53 contains
a) 53 neutrons b) 53 protons C) 26 neutrons & 27 protons d) 26 protons & 27 neutrons
_______2. The mass of one atom of an isotope is 9.746 x 10-23 g. One atomic mass unit
has the mass of 1.6606 x 10-24 g. The atomic mass of this isotope is
a) 5.870 amu
b) 16.18 amu
c) 58.69 amu
d) 1.627 amu
108
_______3. The number of neutrons in an atom of
a) 47
b) 108
c) 155
47
Ag is
d) 61
27
_______4. The number of electrons in an ion of
a) 13
b) 10
c) 27
13
Al3+ is
d) 14
_______5. What is the relative atomic mass of boron if two stable isotopes of boron
have the following mass and abundance:
10.0129 amu (19.91%) & 11.0129 (80.09%)
a) 10.81 amu
b) 10.21 amu
c) 10.62 amu
d) 10.51 amu