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Transcript
Isotopic Notation
Chemistry 11
Definition of an Isotope

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
Understanding 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 (21) is equal to the
number of protons.
Practice these:
15N
35P
7
7
8
# protons = ____
# neutrons= ____
# electrons = ___
15
# p+ = ____
62Cu2+
29
# p+ = ____
20
# n = ____
15
#e- = ___
33
# n = ____
27
#e- = ___
42
# n = ____
37
#e- = ___
76Se3-
34
# p+ = ____
Practice these
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 atom with 23
protons, 26 neutrons and 20 electrons. 49 3+
V
3.
Write the isotopic notation for
110Pd
52Cr3+
a. Z = 46
A = 110
b. An atom containing 24 protons, 28 neutrons, and 21
electrons
c. Titanium-50 50Ti
Practice Problems
1. 196 Pt4+
78 # n = _____
118
# p = _____
74
# e- = _____
196
mass number = ________
78
atomic number = _______
amu
atomic mass = 195.1
________
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.
Calculating Atomic Mass




If you look at your periodic table, for hydrogen, the
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.
Mass Spectrometer

An instrument called the mass spectrometer
is generally used to determine the percentages
and individual masses of each isotope.
Sample Problem

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?
Solution
The equation to use is:
%X + % Y = average atomic mass
And remember to convert your percentage amounts into
fractions (by dividing by 100) before you begin anything!
(0.5182) 106.904 amu + (0.4818) 108.905 amu = mass
55.398 amu + 52.470 amu = 107.868 amu
Now look at the periodic table to verify the answer.
Try This:
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
Group Problems
1.
a)
b)
c)
d)
The element with atomic number 53 contains:
53 neutrons
53 protons
26 neutrons & 27 protons
26 protons & 27 neutrons
2. The number of neutrons in an atom of
a) 47
b) 108
c) 155
d) 61
3. The number of electrons in an ion of
a) 13
b) 10
c) 27
d) 14
47
27
Ag is:
3+ is:
Al
13