Download Isotopes and Mass Number

Warm Up Monday 1/25/16
1. What are atoms?
 2. parts of the atom
mass
charge
 3. Define atomic number.
 4. What does the atomic mass
indicate?
 5. In a atom (no charge) what two sub
atomic particles are equal?
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Isotopes and Mass Number
Atomic Number
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The number of protons in each atom identifies it as an atom of a
particular element
Each atom has a unique number of protons and, in effect, the
number of protons cannot change for a particular atom
The Periodic Table is organized by increasing atomic number
(left-to-right and top-to-bottom)
All atoms are neutral, so the # protons = the # of electrons
because the number of positive charges equals the number of
negative charges
Atomic # = # of protons = # electrons
For Helium, the atomic # is 2. So, we
know that Helium also has 2 protons
and 2 electrons
Determining the State of Matter of a Particular Element Using
the Periodic Table
How Atoms Differ
The order of the
elements on the
Periodic Table is
based on the
number of protons
in the nucleus.
Protons are the only thing in an atom that does not
change.
Proton, Neutron, Electron Practice
How many protons does
Platinum have?
How many neutrons
does Mercury have?
How many electrons
does Lead have?
The number of protons in the nucleus is called
the atomic number. Also since the positive
charges must equal the negative charges to have
a neutral atom, and all atoms are neutral, the
atomic number will also equal the number of
electrons in an atom.
What is the atomic number of
this atom?
What is the element?
What similarities do
these three elements
share?
Isotopes
Don't be an isodope, learn about an isotope.
All atoms of a particular element
have the same number of
protons and electrons
The number of neutrons may
differ
In nature most elements are
found as a mixture of isotopes
Isotopes and Mass
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Isotopes differ in mass
Isotopes of an atom have the same chemical
behavior. Why?
?
Mass Number
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Identifies each of the isotopes of an element
107 Ag
47
109 Ag
47
Mass number = top
Atomic number = bottom
# neutrons = mass # - atomic #
Isotopic Notation Worksheet
Symbol Isotope Atomic # # p+ # n0
Name
3H
20F
24Si
56
76
Mass # # e-
Banana Isotope
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93.25% of K atoms have 20 neutrons
6.7302% of K atoms have 22 neutrons
.0117% of K atoms have 21 neutrons
Potassium Isotope
Potassium-39 Potassium-40 Potassium-41
protons
19
19
19
neutrons
20
21
22
electrons
19
19
19
Mass of Individual Atoms
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The atomic mass of an element is the
weighted average mass of the isotopes of
that element
To determine the weighted average atomic
mass of an element, calculate the mass
contribution of each of the isotopes and add
the values together
Weighted Average Atomic Mass
35
17Cl
37
17Cl
Atomic mass: 34.969 amu
Atomic mass: 36.966 amu
Percent abundance: 75.770%
Mass Contribution:
(34.969)(.75770)= 26.496 amu
% abundance: 24.230%
Mass Contribution:
(36.966)(.24230)=8.957 amu
Weighted average atomic mass of chlorine =
(26.496 amu + 8.957 amu) = 35.453 amu
Steps to Solving Weighted Averages of
Isotopes
1. Turn the % into a decimal for the % abundance.
2. Multiply the decimal by the atomic mass of each
particular isotope.
3. Add the masses of the isotopes together.
4. Your answer will be in amu’s (atomic mass units).
You try one…..
Calculate the atomic mass of Magnesium.
The three Magnesium isotopes have atomic
masses and relative abundances of 23.985
amu (79.99%), 24.986 amu (10.00%), and
25.982 amu (11.01%).
Weighted Averages of Isotopes Practice I
1. What is the atomic mass of this sample of
Silver?
107 Ag
106.905 amu
52 %
109 Ag
108.905 amu
48 %
2. What is the average atomic mass of this
sample of Hydrogen?
1H
12 %
2H
48 %
3H
40 %
Weighted Averages of Isotopes Practice I
Continued
3. Boron has two naturally occurring isotopes,
Boron-10 (abundance 19.8%, mass = 10.013
amu, Boron –11 ( abundance 80.2%, mass =
11.009 amu). Calculate the average atomic
mass of Boron.