Name ____________________________________________________________ Date ___________________
The Structure of the Atom
Section 3 How Atoms Differ
Skim Section 3 of your text. Focus on the headings, boldfaced words, and
main ideas. Then summarize the main ideas of this section.
all reasonable responses.
1. Accept
_____________________________________________________
2. _____________________________________________________
3. _____________________________________________________
In the left margin, write the term defined below.
atomic number
___________________
the number of protons in an atom
isotope
___________________
atoms with the same number of protons but different numbers of neutrons
mass number
___________________
the sum of the number of protons and neutrons in the nucleus
___________________
atomic
mass unit (amu)
atomic mass
___________________
were actually
a stream of
charged
particles.
specific
Chemistry: Matter and Change
1/12 the mass of a carbon-12 atom; the standard unit of measurement for
the mass of atoms
the weighted average mass of the isotopes of an element
Define the following term.
characterized by precise formulation or accurate restriction
________________________________________________________
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Science Notebook
Name ____________________________________________________________ Date ___________________
Section 3 How Atoms Differ (continued)
Atomic Number
Use with page 115.
Explain how to use an atomic number to identify an element by
completing the paragraph below.
protons Since
atom
Each _________
of an element has a unique number of __________.
neutral the number of _________
protons equals
the overall charge of an atom is _________
protons  number
electrons Atomic number  number of ________
the number of _________.
electrons If you know how many one of the three an atom contains,
of ___________.
atomic number
two
you also know the other _________.
Once you know the _______________,
element
periodic table can be used to find the name of the _____________.
the ________________
Atomic Number
Solve Read Example Problem 1 in your text.
Use with Example
Problem 1, page 116.
You Try It
Problem
Given the following information about atoms, determine the name of each
atom’s element and its atomic number.
a. Atom 1 has 11 protons
b. Atom 2 has 20 electrons
1. Analyze the Problem
Apply the relationship among atomic number, number of protons, and
number of electrons to determine the name and atomic number of each
element.
2. Solve for the Unknown
a. Atom 1
Atomic number  number of protons  number of electrons
11
Atomic number  ________
 number of electrons
sodium (Na)
The element with an atomic number of 11 is _______________
b. Atom 2
Atomic number  number of protons  number of electrons
20
Atomic number  number of protons  ______
calcium (Ca)
20
The element with an atomic number of __________
is _____________.
3. Evaluate the Answer
atomic numbers and element
The answers agree with ____________________
symbols
___________________________
given in the periodic table.
Chemistry: Matter and Change
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Science Notebook
Name ____________________________________________________________ Date ___________________
Section 3 How Atoms Differ (continued)
Isotopes and
Mass Number
Use with page 117.
Review your understanding of isotopes and mass number by completing
the following paragraph.
the same number of protons but with
Isotopes are elements with ______________________________
differing numbers of neutrons The number of neutrons can be
_______________________________.
subtracting
determined by _________________
the atomic number from the
mass number
____________________
. The mass number is
the number of protons plus neutrons in an atom
_________________________________________________________
.
Use Atomic
Number and
Mass Number
Use with Example
Problem 2, page 118.
Solve Read Example Problem 2 in your text.
You Try It
Problem
You are given two samples of carbon. The first sample, carbon-12, has a
mass number of 12, the second sample, carbon-13, has a mass number
of 13. Both samples have an atomic number of 6. Determine the
number of protons, electrons, and neutrons in each sample.
1. Analyze the Problem
Known:
Carbon-12
Carbon-13
12
Mass number is _______
13
Mass number is _______
6
Atomic number is ______
6
Atomic number is ______
Unknown:
The number of protons, electrons, and neutrons in each sample.
2. Solve for the Unknown
6
Number of protons = number of electrons = atomic number = _____
Number of neutrons = mass number  atomic number
6
The number of neutrons for carbon-12 = 12  6 = _______
7
The number of neutrons for carbon-13 = 13  6 = _______
3. Evaluate the Answer
mass number minus
The number of neutrons does equal the __________________
atomic number or the number of protons.
the _________________,
Chemistry: Matter and Change
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Science Notebook
Name ____________________________________________________________ Date ___________________
Section 3 How Atoms Differ (continued)
Mass of Atoms
Use with pages 119–120.
Explain why the mass number for chlorine is more than 35.
Elements
can have several isotopes. Each isotope has a different number of
________________________________________________________
neutrons. Therefore each isotope has a different mass. The atomic mass of an
________________________________________________________
element is a weighted average mass of all the isotopes of that element.
________________________________________________________
Calculate
Atomic Mass
Use with Example
Problem 3, page 121.
Summarize Fill in the blanks to help you take notes while you read
Example Problem 3.
Problem
calculate the
data
Given the __________
in the table in the left margin, ____________
atomic mass of unknown element X. Then, _________
identify the unknown
______________
Isotope Abundance for
Element X
Isotope
6
7
Mass
Percent
(amu) abundance
X
6.015
7.59%
X
7.016
92.41%
medically to treat some _________________.
mental disorders
element which is used __________
________,
1. Analyze the problem
Known:
Unknown:
atomic mass
_________________
of X  ? amu
6
For isotope X:
name
6.015 amu
mass  _________________
___________
of element X  ?
7.59%  0.0759
abundance  ____________________
For isotope 7X:
7.016 amu
mass  ________________
92.41%  0.9241
abundance  ____________________
2. Solve for the unknown
mass
percent abundance
Mass contribution  (________)
(_____________________________)
0.4565amu
(6.015 amu)(0.0759)  ___________
For 6X: Mass contribution  ____________________
6.483amu
amu)(0.9241)  __________
For 7X: Mass contribution  (7.016
____________________
Sum the mass contributions to find the atomic mass.
6.939 amu
Atomic mass of X  _________________________
(0.4565 amu + 6.483 amu)  __________
_____________
periodic table
Use the ____________________
to identify the element.
lithium
The element with an atomic mass of 6.939 amu is __________.
3. Evaluate the answer
mass number minus the
The number of neutrons does equal the ________________
protons
atomic number
______________________,
or number of ____________.
Chemistry: Matter and Change
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Science Notebook